This chapter provides an in-depth review of the micronutrients necessary during lifespan development to give students a better understanding of how micronutrient needs change as a person ages. The following chapter, Aging Information, provides a more specific look at the changing nutrient requirements in older age. This chapter is meant to give students a refresher of HNU 351 Nutrition Assessment and summarizes this information for those who did not take this class.  

5.1 Fat-Soluble Vitamins

Vitamin A is fat-soluble and is packaged into chylomicrons in the small intestine and transported to the liver. The liver stores and exports Vitamin A as needed; it is released into the blood and transported to cells. Carotenoids are not absorbed as well as Vitamin A, but like Vitamin A, they require fat in the meal for absorption. In intestinal cells, carotenoids are packaged into lipid-containing chylomicrons and then transported to the liver. In the liver, carotenoids are repackaged into lipoproteins, which transport them to cells.

The retinoids are aptly named as their most notable function is in the retina of the eye, where they aid in vision, particularly in seeing under low-light conditions. Therefore, night blindness is the most definitive sign of Vitamin A deficiency. Vitamin A has several vital functions in the body, including maintaining vision and a healthy immune system. Many of Vitamin A’s roles are like hormone functions  (for example, Vitamin A can interact with DNA, causing a change in protein function). Vitamin A helps maintain healthy skin, the linings and coverings of tissue, and regulates growth and development. As an antioxidant, Vitamin A protects cellular membranes, helps maintain glutathione levels, and influences enzyme activity in detoxifying free radicals. 

Vision

Retinol circulating in the blood is taken up by cells in the eye retina, where it is converted to retinal and is involved in the eye’s ability to see under low light conditions. A deficiency in Vitamin A thus, results in a decrease in the detection of low-level light, a condition referred to as night blindness.

Insufficient intake of dietary Vitamin A over time can also cause complete vision loss. Vitamin A deficiency is the number one cause of preventable blindness worldwide. Vitamin A not only supports the vision function of the eyes but also maintains the covers and linings of the eyes. Vitamin A deficiency can lead to the dysfunction of the linings and coverings of the eye (e.g., bitot spots), causing dryness of the eyes, a condition called xerophthalmia. The progression of this condition can cause ulceration of the cornea and eventually blindness.

Immunity

The common occurrence of advanced xerophthalmia in children who died from infectious diseases led scientists to hypothesize that supplementing Vitamin A in the diet for children with xerophthalmia might reduce disease-related mortality. In Asia in the late 1980s, targeted populations of children were administered Vitamin A supplements, and the death rates from measles and diarrhea declined by up to 50 percent (Sommer, 2008). Vitamin A supplementation in these deficient populations did not reduce the number of children who contracted these diseases, but it did decrease the severity of the diseases so that they were no longer fatal. Soon after the results of these studies were communicated to the rest of the world, the World Health Organization (W.H.O.) and the United Nations Children’s Fund (U.N.I.C.E.F.) commenced worldwide campaigns against Vitamin A deficiency. U.N.I.C.E.F. estimates that the distribution of over half a billion Vitamin A capsules prevents 350,000 childhood deaths annually (Sommer, 2008).

In the twenty-first century, science has demonstrated that Vitamin A greatly affects the immune system. We still need clinical trials investigating the proper doses of Vitamin A required to help ward off infectious disease and how much Vitamin A supplementation affects populations that are not deficient (Sommer, 2008). Micronutrient deficiencies may contribute to a disease’s development, progression, and severity, but this does not mean an increased intake of these micronutrients will solely prevent or cure disease. The effect, as usual, is cumulative and depends on the diet, among other things.

Growth and Development

Vitamin A acts similarly to some hormones in that it can change the number of proteins in cells by interacting with DNA. This is the primary way that Vitamin A affects growth and development. Vitamin A deficiency in children is linked to growth retardation; however, Vitamin A deficiency is often accompanied by protein malnutrition and iron deficiency, thereby confounding the investigation of Vitamin A’s specific effects on growth and development.

In the fetal stages of life, Vitamin A is important for limb, heart, eye, and ear development and in both deficiency and excess, Vitamin A causes congenital disabilities. Further, males and females require Vitamin A in the diet to reproduce effectively.

Cancer

Vitamin A’s role in regulating cell growth and death, especially in tissues that line and cover organs, suggests it may be effective in treating certain lung, neck, and liver cancers. It has been shown in some observational studies that Vitamin A-deficient populations have a higher risk for some cancers. However, Vitamin A supplements have been found to increase the risk of lung cancer in people at high risk for the disease (i.e., smokers, ex-smokers, and workers exposed to asbestos). The Beta-Carotene and Retinol Efficacy Trial (C.A.R.E.T.) involved over eighteen thousand participants at high risk for lung cancer. This trial found that people who took supplements containing very high doses of Vitamin A (25,000 international units) and beta-carotene had a 28 percent higher incidence of lung cancer midway through the study, which was consequently stopped (Goodman, 2004).

Vitamin A Toxicity

Vitamin A toxicity, or hypervitaminosis A, is rare. Typically, it requires intakes ten times the RDA of preformed Vitamin A in the form of supplements (it would be hard to consume such high levels from a regular diet) for a substantial amount of time. However, some people may be more susceptible to Vitamin A toxicity at lower doses. The signs and symptoms of Vitamin A toxicity include dry, itchy skin, loss of appetite, swelling of the brain, and joint pain. In severe cases, Vitamin A toxicity may cause liver damage and coma.

Vitamin A is essential during pregnancy, but doses above 3,000 micrograms per day (10,000 international units) have been linked to an increased incidence of congenital disabilities. Pregnant women should check the amount in any prenatal or pregnancy multivitamin she takes to ensure the amount is below the UL.

Dietary Reference Intakes for Vitamin A

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Vitamin A and Beta-Carotene

Preformed Vitamin A is found only in foods of animal origin, with the liver being the richest source because that’s where Vitamin A is stored. Table 5.1.2 provides the Vitamin A content of foods containing preformed Vitamin A.

Table 5.1.2: Vitamin A Content of Foods Containing Preformed Vitamin A

Source: Dietary Supplement Fact Sheet: Vitamin A. National Institutes of Health, Office of Dietary Supplements. Updated September 5, 2012. Accessed October 7, 2017.

In North America, the most consumed carotenoids are alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin. See Table 5.1.3 for the carotenoid content of various foods.

Table 5.1.3: Vitamin A Content of Various Carotenoid-containing Foods

Source: 2010. USDA National Nutrient Database for Standard Reference, Release 23. US Department of Agriculture, Agricultural Research Service. Accessed October 22, 2017.

Vitamin D

Vitamin D refers to a group of fat-soluble Vitamins derived from cholesterol. Vitamins D2 (ergocalciferol) and D3 (calcitriol) are the only ones that have biological actions in the human body. The skin synthesizes Vitamin D when exposed to sunlight. In fact, for most people, more than 90 percent of their Vitamin D3 comes from casual exposure to UVB rays in sunlight. Anything that reduces exposure to the sun’s UVB rays decreases the amount of Vitamin D3 your skin synthesizes. That would include long winters, your home’s altitude, whether you are wearing sunscreen, and skin colour (including tanned skin). Do you ever wonder about an increased risk of skin cancer by spending too much time in the sun? Do not fret. Less than thirty minutes of sun exposure to the arms and legs will increase blood levels of Vitamin D3 more than taking 10,000 I.U. (250 micrograms) of Vitamin D3.

Vitamin D’s Functional Role

Activated Vitamin D3 (calcitriol) regulates blood calcium levels in concert with the parathyroid hormone and is critical for bone health. Less than 15 percent of calcium is absorbed from foods or supplements without adequate Vitamin D intake.  A deficiency of Vitamin D in children causes a bone disease called nutritional rickets. Rickets is very common among children in developing countries and is characterized by soft, weak, deformed bones that are exceptionally susceptible to fracture. Vitamin D deficiency may also cause a similar disease called osteomalacia, characterized by low bone mineral density (BMD). Osteomalacia has the same symptoms and consequences as osteoporosis and often coexists with osteoporosis. Vitamin D deficiency may be common in the population, especially in the elderly population, dark-skinned populations, and in the many people who live in the northern latitudes where sunlight exposure is much decreased during the long winter season.

Health Benefits

Observational studies have shown that people with low levels of Vitamin D in their blood have lower bone mineral density and an increased incidence of osteoporosis. In contrast, diets with high intakes of salmon, which contain a large amount of Vitamin D, are linked with better bone health. Unfortunately, current evidence does not demonstrate that large doses of supplemental Vitamin D improve bone density (Bolland, Grey & Avenell, 2018).  Safe sun exposure (10-30 minutes of mid-day sun on the arms and legs two to three times per week) and food sources of Vitamin D are your best plan of action.

Many other health benefits have been linked to Vitamin D, from decreased cardiovascular disease to infection prevention. Furthermore, evidence from laboratory studies conducted in cells, tissues, and animals suggests Vitamin D prevents the growth of certain cancers, blocks inflammatory pathways, reverses atherosclerosis, increases insulin secretion, and blocks viral and bacterial infection and many other things. Vitamin D deficiency has been linked to an increased risk of autoimmune diseases. Immune diseases, rheumatoid arthritis, multiple sclerosis, and Type 1 diabetes have been observed in populations with inadequate Vitamin D levels. Additionally, Vitamin D deficiency is linked to an increased incidence of hypertension. Most scientific evidence describing other health benefits of Vitamin D is from laboratory and observational studies and requires confirmation in clinical intervention studies. This is an example of how the findings in observational and lab studies may not be the same as intervention studies. To date, interventional studies have been inconclusive regarding supplementation and the other potential roles of Vitamin D in the body (Bolland, Grey & Avenell, 2018).

Vitamin D Toxicity

Although Vitamin D toxicity is rare, too much can cause calcium concentrations or hypercalcemia. Hypercalcemia can lead to a large amount of calcium being excreted through the urine, which can cause kidney damage. Calcium deposits may also develop in soft tissues such as the kidneys, blood vessels, cardiovascular system. However, it is important to know that synthesizing Vitamin D from the sun does not cause Vitamin D toxicity because the skin production of Vitamin D3 is a tightly regulated process.

Dietary Reference Intake for Vitamin D

The Institute of Medicine RDA for Vitamin D is listed in Table 5.1.4. The National Osteoporosis Foundation recommends slightly higher levels and that adults under age fifty get between 400 and 800 international units of Vitamin D every day, and adults fifty and older get between 800 and 1,000 international units of Vitamin D every day. Toxicity from excess Vitamin D is rare, but certain diseases such as hyperparathyroidism, lymphoma, and tuberculosis make people more sensitive to the increases in calcium caused by high intakes of Vitamin D.

Table 5.1.4: Dietary Reference Intakes for Vitamin D (mcg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Table 5.1.5: Dietary Sources of Vitamin D (IU; conversion 1IU = 0.025 mcg).

Source: Dietary Supplement Fact Sheet: Vitamin D. National Institutes of Health, Office of Dietary Supplements. Updated September 5, 2012. Accessed October 22, 2017.

Vitamin E

Vitamin E occurs in eight chemical forms, of which alpha-tocopherol appears to be the only form recognized to meet human requirements. Alpha-tocopherol and Vitamin E’s other constituents are fat-soluble and primarily responsible for protecting cell membranes against lipid destruction caused by free radicals, making it an antioxidant. When alpha-tocopherol interacts with a free radical, it can no longer act as an antioxidant unless it is enzymatically regenerated. Vitamin C helps to regenerate some of the alpha-tocopherol, but the remainder is eliminated from the body. Therefore, to maintain Vitamin E levels, you must ingest it as part of your diet.

Insufficient levels are rare (signs and symptoms of such conditions are not always evident) but primarily the cause of nerve degeneration. People with malabsorption disorders, such as Crohn’s disease or cystic fibrosis, and babies born prematurely, are at higher risk for Vitamin E deficiency (Goodman et al., 2011).

Vitamin E has many other important roles and functions in the body, such as boosting the immune system by helping to fight off bacteria and viruses. It also enhances the dilation of blood vessels and inhibits the formation of blood clotting. Despite Vitamin E’s numerous beneficial functions when taken in recommended amounts, large studies do not support the idea that taking higher doses of this Vitamin will increase its power to prevent or reduce disease risk (McGinley, Shafat & Donnelly, 2009).

Fat in the diet is required for Vitamin E absorption as it is packaged into lipid-rich chylomicrons in intestinal cells and transported to the liver. The liver stores some of the Vitamin E or packages it into lipoproteins, which deliver it to cells.

Cardiovascular Disease

Vitamin E reduces the oxidation of LDLs, and it was therefore hypothesized that Vitamin E supplements would protect against atherosclerosis. However, large clinical trials have not consistently found evidence to support this hypothesis. In the “Women’s Angiographic Vitamin and Estrogen Study,” postmenopausal women who took 400 international units (264 milligrams) of Vitamin E and 500 milligrams of Vitamin C twice per day had higher death rates from all causes (Waters et al., 2002).

Other studies have not confirmed the association between increased Vitamin E intake from supplements and increased mortality. There is more consistent evidence from observational studies that a higher intake of Vitamin E from foods is linked to a decreased risk of dying from a heart attack.

Cancer

The large clinical trials that evaluated whether there was a link between Vitamin E and cardiovascular disease risk also looked at cancer risk. These trials, called the HOPE-TOO Trial and Women’s Health Study did not find that Vitamin E at doses of 400 international units (264 milligrams) per day or 600 international units (396 milligrams) every other day reduced the risk of developing any form of cancer (Lonn et al., 2005; Lee et al., 2005).

Vitamin E Toxicity

Researchers have not found any adverse effects from consuming Vitamin E in food. Although that may be the case, supplementation of alpha-tocopherol in animals has been shown to cause hemorrhage and disrupt blood coagulation. Extremely high levels of Vitamin E can interact with Vitamin K-dependent clotting factors causing inhibition of blood clotting (Dietary Supplement Fact Sheet: Vit.E, 2018).

Vitamin E supplements often contain more than 400 international units, almost twenty times the RDA. The UL for Vitamin E is set at 1,500 international units for adults. There is some evidence that taking Vitamin E supplements at high doses has negative health effects. As mentioned, Vitamin E inhibits blood clotting and a few clinical trials have found that people taking Vitamin E supplements have an increased risk of stroke. In contrast to Vitamin E from supplements, there is no evidence that consuming foods containing Vitamin E compromises health.

Dietary Reference Intakes for Vitamin E

The Recommended Dietary Allowance (RDA) and Tolerable Upper Intake Level (UL) for older adults for Vitamin E are given in Table 5.1.6.

Table 5.1.6: Dietary Reference Intakes for Vitamin E (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Vitamin E

Add some nuts to your salad and make your own dressing to get a healthy dietary dose of Vitamin E.

Vitamin E is found in many foods, especially those higher in fat, such as nuts and oils. Some spices, such as paprika and red chili pepper, and herbs, such as oregano, basil, cumin, and thyme, also contain Vitamin E. (Keep in mind spices and herbs are commonly used in small amounts in cooking and therefore are a lesser source of dietary Vitamin E.) See Table 5.1.7 for a list of foods and their Vitamin E content.

Everyday Connection

To increase your dietary intake of Vitamin E from plant-based foods try a spinach salad with tomatoes and sunflower seeds, and add a dressing made with sunflower oil, oregano, and basil.

Table 5.1.7: Dietary Sources of Vitamin E

Source: Dietary Supplement Fact Sheet: Vitamin E. National Institutes of Health, Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/VitaminE-QuickFacts/. Updated August 17, 2018. Accessed June 30, 2019.

Vitamin K

Vitamin K refers to a group of fat-soluble vitamins that are similar in chemical structure. Vitamin K is critical for blood function, acting as coenzymes which play an essential role in blood coagulation (aka blood clotting). Blood-clotting proteins are continuously circulating in the blood. Upon injury to a blood vessel, platelets stick to the wound forming a plug. Without Vitamin K, blood would not clot.

A deficiency in Vitamin K causes bleeding disorders. It is relatively rare, but people who have liver or pancreatic disease, celiac disease, or malabsorption conditions are at higher risk for Vitamin K deficiency. Signs and symptoms include nosebleeds, easy bruising, broken blood vessels, bleeding gums, and heavy menstrual bleeding in women. The function of the anticoagulant drug warfarin is impaired by excess Vitamin K intake from supplements. Calcium additionally plays a role in the activation of blood-clotting proteins.

Bone Health

Vitamin K is also required for maintaining bone health. It modifies the protein osteocalcin, which is involved in the bone remodelling process. All the functions of osteocalcin and the other Vitamin K-dependent proteins in bone tissue are not well understood and are under investigation. Some studies show that people with diets low in Vitamin K also have an increased risk for bone fractures.

Dietary Reference Intake and Food Sources for Vitamin K

The Food and Nutrition Board (FNB) has not established a UL for Vitamin K because it has a low potential for toxicity. According to the FNB, “no adverse effects associated with Vitamin K consumption from food or supplements have been reported in humans or animals” (Institute of Medicine, 2001).

Table 5.1.8: Dietary Reference Intakes for Vitamin K (mcg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Vitamin K

Vitamin K is present in many foods. It is found in the highest concentrations in green vegetables such as broccoli, cabbage, kale, parsley, spinach, and lettuce. Additionally, Vitamin K can be synthesized via bacteria in the large intestine. The amount of Vitamin K synthesized by bacteria and absorbed in the lower intestine is unknown but likely contributes less than 10 percent of the recommended intake. Newborns have low Vitamin K stores, and it takes time for their sterile gut to acquire the bacteria to produce Vitamin K. It has become a routine practice to give newborns a single intramuscular or oral dose of Vitamin K. This practice has eliminated Vitamin K-dependent bleeding disorders in babies. In populations where parents refuse this practice, physicians are seeing increased rates of blood clotting problems in newborns (Schulte et al., 2014).

Table 5.1.9: Dietary Sources of Vitamin K.

Summary of Fat-soluble Vitamins

Table 5.1.10 provides a summary of the fat-soluble vitamins.

Table 5.1.10: Fat-soluble Vitamins Summary Table

Vitamin C

Vitamin C, also called ascorbic acid, is a water-soluble micronutrient essential in the diet for humans, although most other mammals can readily synthesize it. Vitamin C’s ability to donate electrons easily makes it a highly effective antioxidant. It is effective in scavenging free radicals. It protects lipids by disabling free radicals and aiding in the regeneration of Vitamin E.

In addition to its role as an antioxidant, Vitamin C is a required part of several enzymes like signaling molecules in the brain, some hormones, and amino acids. Vitamin C is also essential for the synthesis and maintenance of collagen. Collagen is the most abundant protein in the body and is used for various functions, such as forming the structure for ligaments, tendons, blood vessels and scars that bind wounds together. Vitamin C is the glue that holds the collagen fibers together; without sufficient levels in the body, collagen strands are weak and abnormal.

Vitamin C levels in the body are affected by the amount in the diet, which influences how much is absorbed and excreted, such that the higher the intake, the more Vitamin C is excreted. Vitamin C is not stored in any significant amount in the body, but once it has been reduced to a free radical, it is very effectively regenerated, and therefore it can exist in the body as an active antioxidant for many weeks.

The classic condition associated with Vitamin C deficiency is scurvy. The signs and symptoms of scurvy include skin disorders, bleeding gums, painful joints, weakness, depression, and increased susceptibility to infections. An adequate intake of fruits and vegetables rich in Vitamin C prevents scurvy.

Vitamin C Toxicity

High doses of Vitamin C have been reported to cause numerous problems, but the only consistently shown side effects are gastrointestinal upset and diarrhea. To prevent these GI discomforts, the IOM has set a UL for adults at 2,000 milligrams per day (greater than twenty times the R.D.A.).

At very high doses in combination with iron, Vitamin C has sometimes been found to increase oxidative stress, reaffirming that getting your antioxidants from foods helps to regulate intake levels and is better than getting them from supplements. There is some evidence that taking Vitamin C supplements at high doses increases the likelihood of developing kidney stones; however, this effect is most often observed in people that already have multiple risk factors for kidney stones.

Dietary Reference Intake for Vitamin C

The dietary reference intakes for older adults for Vitamin C are listed in Table 5.2.1. They are considered adequate to prevent scurvy. Vitamin C’s effectiveness as a free radical scavenger motivated the Institute of Medicine (IOM) to increase the RDA for smokers by 35 milligrams, as tobacco smoke is an environmental and behavioural contributor to free radicals in the body.

Table 5.2.1: Dietary Reference Intakes for Vitamin C (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Vitamin C

Citrus fruits are excellent sources of Vitamin C, as are many vegetables. British sailors in the past were often referred to as “limeys” as they carried sacks of limes onto ships to prevent scurvy. Vitamin C is not found in significant amounts in animal-based foods. Because Vitamin C is water-soluble, it leaches away from foods considerably during cooking, freezing, thawing, and canning. Up to 50 percent of Vitamin C can be boiled away. Therefore, to maximize Vitamin C intake from foods, you should eat fruits and vegetables raw or lightly steamed. For the Vitamin C content of various foods, see Table 5.2.2.

Table 5.2.2: Vitamin C Content of Various Foods

Source: Dietary Supplement Fact Sheet: Vitamin C. National Institutes of Health, Office of Dietary Supplements. Updated September 18, 2018. Accessed June 30, 2019.

Thiamin (B1)

Thiamin is essential in glucose metabolism. It acts as a cofactor for enzymes that break down glucose for energy production. Thiamin plays a key role in nerve cells as the glucose that is catabolized by thiamin is needed for an energy source. Additionally, thiamin plays a role in the synthesis of neurotransmitters and is therefore required for RNA, DNA, and A.T.P. synthesis.

The brain and heart are most affected by a deficiency in thiamin. Thiamin deficiency, also known as beriberi, can cause symptoms of fatigue, confusion, movement impairment, pain in the lower extremities, swelling, and heart failure. It is prevalent in societies whose main dietary staple is white rice. During the processing of white rice, the bran is removed, along with what were called in the early nineteenth century, “accessory factors,” which are vital for metabolism. Dutch physician Dr. Christiaan Eijkman cured chickens of beriberi by feeding them unpolished rice bran in 1897. By 1912, Sir Frederick Gowland Hopkins determined from experiments with animals that the “accessory factors,” eventually renamed vitamins, are needed in the diet to support growth since animals fed a diet of pure carbohydrates, proteins, fats, and minerals failed to grow. Eijkman and Hopkins were awarded the Nobel Prize in Physiology (or Medicine) in 1929 for their discoveries in the emerging science of nutrition.

Dietary Reference Intakes of Thiamin

The dietary reference intakes for older adults for thiamin are listed in Table 5.2.3. There is no UL for thiamin because there have not been any reports of toxicity when excess amounts are consumed from food or supplements.

Table 5.2.3: Dietary Reference Intakes for Thiamin(mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Thiamin

Whole grains, meat, and fish are great sources of thiamin. Some countries fortify their refined bread and cereals. In Canada, there are both voluntary and mandatory guidelines for thiamine fortification to help Canadian’s increase their dietary consumption. As outlined by the Government of Canada (2022), fortification guidelines for thiamin in Canada are as follows:

For the thiamin content of various foods, see Table 5.2.4.

Table 5.2.4: Thiamin Content of Various Foods

Source: Health Professional Fact Sheet: Thiamin. National Institutes of Health, Office of Dietary. Updated February 11, 2016. Accessed October 5, 2017.

Riboflavin (B2)

Riboflavin is an essential component of flavoproteins, which are coenzymes involved in many metabolic pathways of carbohydrate, lipid, and protein metabolism. Flavoproteins aid in the transfer of electrons in the electron transport chain. Furthermore, the functions of other B-vitamin coenzymes, such as Vitamin B6 and folate, depend on flavoproteins’ actions. The “flavin” portion of riboflavin gives a bright yellow colour to riboflavin, an attribute that helped lead to its discovery as a vitamin. When riboflavin is taken in excess amounts (supplement form), the excess will be excreted through your kidneys and show up in your urine. Although the colour may alarm you, it is harmless. No adverse effects of high doses of riboflavin from foods or supplements have been reported.

Riboflavin deficiency sometimes referred to as ariboflavinosis, is often accompanied by other dietary deficiencies (most notably protein) and can be common in people that suffer from alcoholism. This deficiency will usually also occur in conjunction with deficiencies of other B vitamins because many B vitamins have similar food sources. The signs and symptoms of riboflavin deficiency include dry, scaly skin, cracking of the lips and corners of the mouth, sore throat, itchy eyes, and light sensitivity.

Dietary Reference Intakes of Riboflavin

The RDAs for different age groups for riboflavin are listed in Table 5.2.5. There is no UL for riboflavin because no toxicity has been reported when an excess amount has been consumed through foods or supplements.

Table 5.2.5: Dietary Reference Intakes for Riboflavin (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Riboflavin

Riboflavin can be found in various foods, but it is important to remember that sunlight can destroy it. Milk is one of the best sources of riboflavin in the diet and was once delivered and packaged in glass bottles. This packaging has changed to cloudy plastic containers or cardboard to help block the light from destroying the riboflavin in milk. For the riboflavin content of various foods see Table 5.2.6.

Table 5.2.6: Riboflavin Content of Various Foods

Source: Fact Sheet for Health Professionals, Riboflavin. National Institute of Health, Office of Dietary Supplements. Updated February 11, 2016. Accessed October 22, 2017.

Niacin (B3)

Niacin is a component of the coenzymes NADH and NADPH, which are involved in the catabolism and/or anabolism of carbohydrates, lipids, and proteins. NADH is the predominant electron carrier and transfers electrons to the electron-transport chain to make ATP. NADPH is also required for the anabolic pathways of fatty-acid and cholesterol synthesis. In contrast to other vitamins, humans can synthesize niacin from the amino acid tryptophan in a process requiring enzymes dependent on riboflavin, Vitamin B6, and iron. Niacin is made from tryptophan only after tryptophan has met all of its other needs in the body. The contribution of tryptophan-derived niacin to niacin needs in the body varies widely. A few scientific studies have demonstrated that diets high in tryptophan have minimal effect on niacin deficiency. Niacin deficiency is commonly known as pellagra, and the symptoms include fatigue, decreased appetite, and indigestion. These symptoms are then commonly followed by the four D’s: diarrhea, dermatitis, dementia, and sometimes death.

Dietary Reference Intakes of Niacin

The RDAs and ULs for different age groups for Niacin are listed in Table 5.2.7. Because Niacin needs can be met from tryptophan, The RDA is expressed in niacin equivalents (NE). The conversions of NE, Niacin, and tryptophan are: 1 mg NE= 60 milligrams tryptophan= 1 mg niacin.

Table 5.2.7: Dietary Reference Intakes for Niacin (NE/day) for adolescents and adults.

Sources: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Niacin

Niacin can be found in various foods such as yeast, meat, poultry, red fish, and cereal. In plants, especially mature grains, niacin can be bound to sugar molecules which can significantly decrease the niacin bioavailability. For the niacin content of various foods, see Table 5.2.8.

Table 5.2.8: Niacin Content of Various Foods

Source: Micronutrient Information Center: Niacin. Oregon State University, Linus Pauling Institute. Updated in July 2013. Accessed October 22, 2017.

Pantothenic Acid (B5)

Pantothenic acid forms coenzyme A, the cell’s primary carrier of carbon molecules. Acetyl-CoA is the carbon carrier of glucose, fatty acids, and amino acids in the citric acid cycle. Coenzyme A is also involved in synthesizing lipids, cholesterol, and acetylcholine (a neurotransmitter). Pantothenic Acid deficiency is exceptionally rare. Signs and symptoms include fatigue, irritability, numbness, muscle pain, and cramps. You may have seen pantothenic acid on many ingredient lists for skin and hair care products; however, there is no good scientific evidence that pantothenic acid improves human skin or hair.

Dietary Reference Intake for Pantothenic Acid

Because there is little information on the requirements for pantothenic acids, the Food and Nutrition Board (FNB) has developed Adequate Intakes (AI) based on the observed dietary intakes in healthy population groups. The AI for different age groups for pantothenic acid is listed in Table 5.2.9.

Table 5.2.9: Adequate Intakes for Pantothenic Acid (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Pantothenic Acid

Pantothenic Acid is widely distributed in all types of food, which is why a deficiency in this nutrient is rare. Pantothenic Acid gets its name from the Greek word “pantothen, “meaning “from everywhere.” For the pantothenic acid content of various foods, see Table 5.3.10.

Table 5.3.10: Pantothenic Acid Content of Various Foods

Source: Micronutrient Information Center: Pantothenic Acid. Oregon State University, Linus Pauling Institute. Updated in July 2013. Accessed October 22, 2017.

Biotin

Biotin is required as a coenzyme in the citric acid cycle and in lipid metabolism. It is also required as an enzyme to synthesize glucose and some nonessential amino acids. A specific enzyme, biotinidase, is necessary to release biotin from protein so that it can be absorbed in the gut. Some bacterial synthesis of biotin occurs in the colon; however, this is not a significant source of biotin. Biotin deficiency is rare but can be caused by eating large amounts of raw egg whites over an extended period. This is because the protein in egg whites tightly binds to biotin, making it unavailable for absorption. A rare genetic disease-causing malfunction of the biotinidase enzyme also results in biotin deficiency. Symptoms of biotin deficiency are like those of other B vitamins but may also include hair loss when severe.

Dietary Reference Intakes of Biotin

Because there is little information on the requirements for biotin, the FNB has developed Adequate Intakes (AI) based on the observed dietary intakes in healthy population groups. The AI for different age groups for biotin is listed in Table 5.2.11.

Table 5.2.11: Adequate Intakes for Biotin (mcg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Biotin

Biotin can be found in foods such as eggs, fish, meat, seeds, nuts, and certain vegetables. For the pantothenic acid content of various foods, see Table 5.2.12.

Table 5.2.12: Biotin Content of Various Foods

Source: Fact Sheet for Health Professionals: Biotin. National Institute of Health, Office of Dietary Supplements. Updated October 3, 2017. Accessed November 10, 2017.

Vitamin B6 (Pyridoxine)

Vitamin B6 is the coenzyme involved in a wide variety of functions in the body. One primary function is the nitrogen transfer between amino acids which plays a role in amino-acid synthesis and catabolism. Also, it functions to release glucose from glycogen in the catabolic glycogenolysis pathway and is required by enzymes to synthesize multiple neurotransmitters and hemoglobin.

Vitamin B6 is also a required coenzyme for the synthesis of hemoglobin. A deficiency in Vitamin B6 can cause anemia, but it is different from that caused by insufficient folate, cobalamin, or iron; although the symptoms are similar. The size of red blood cells is normal or somewhat smaller, but the hemoglobin content is lower. This means each red blood cell has less capacity for carrying oxygen, resulting in muscle weakness, fatigue, and shortness of breath. Other deficiency symptoms of Vitamin B6 can cause dermatitis, mouth sores, and confusion.

Transamination reactions transfer an amino acid group to a carbon group. Decarboxylation reactions remove the acid group (COOH) from an amino acid to be used for neurotransmitter synthesis. Deamination reactions remove an amino group from an amino acid to use for energy production and glucose synthesis.

The Vitamin B6 coenzyme is needed for many different reactions essential for amino acid synthesis, catabolism for energy, and the synthesis of glucose and neurotransmitters.

Vitamin B6 coenzyme is essential for converting amino acid methionine into cysteine. With low levels of Vitamin B6, homocysteine will build up in the blood. High levels of homocysteine increase the risk of heart disease.

Vitamin B6 Toxicity

Currently, no adverse effects have been associated with a high dietary intake of Vitamin B6, but large supplemental doses can cause severe nerve impairment. To prevent this from occurring, the UL for adults is set at 100 mg/day.

Dietary Reference Intakes of Vitamin B6

The RDAs and ULs for different age groups for Vitamin B6 are listed in Table 5.2.13.

Table 5.2.13: Dietary Reference Intakes for Vitamin B6 (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Vitamin B6

Vitamin B6 can be found in a variety of foods. The richest sources include fish, beef liver and other organ meats, potatoes, and other starchy vegetables and fruits. For the Vitamin B6 content of various foods, see Table 5.2.14.

Table 5.2.14: B6 Content of Various Foods

Dietary Supplement Fact Sheet: Vitamin B6. National Institute of Health, Office of Dietary Supplements. Updates February 11, 2016. Accessed October 22, 2017.

Folate

Folate is a required coenzyme for the synthesis of the amino acid methionine, and for making RNA and DNA. Therefore, rapidly dividing cells are most affected by folate deficiency. Red blood cells, white blood cells, and platelets are continuously being synthesized in the bone marrow from dividing stem cells. When folate is deficient, cells cannot divide normally. A consequence of folate deficiency is macrocytic or megaloblastic anemia. Macrocytic and megaloblastic mean “big cell,” and anemia refers to fewer red blood cells or red blood cells containing less hemoglobin. Macrocytic anemia is characterized by larger and fewer red blood cells. It is caused by red blood cells being unable to produce DNA and RNA fast enough—cells grow but do not divide, making them large in size.

Folate is especially essential for the growth and specialization of cells of the central nervous system. Children whose mothers were folate-deficient during pregnancy have a higher risk of neural-tube congenital disabilities. Folate deficiency is causally linked to the development of spina bifida, a neural-tube defect that occurs when the spine does not completely enclose the spinal cord. Spina bifida can lead to many physical and mental disabilities. Observational studies show that the prevalence of neural-tube defects decreased after the fortification of enriched cereal grain products with folate in 1996 in the United States (and 1998 in Canada) compared to before grain products were fortified with folate.

Additionally, results of clinical trials have demonstrated that neural-tube defects are significantly less than in the offspring of mothers who began taking folate supplements one month prior to becoming pregnant and throughout the pregnancy. In response to the scientific evidence, the Food and Nutrition Board of the Institute of Medicine (I.O.M.) raised the R.D.A. for folate to 600 micrograms per day for pregnant women. Some were concerned that higher folate intake may cause colon cancer, however scientific studies refute this hypothesis.

Table 5.2.15: Dietary Reference Intakes for Folate (DFE/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Folate

Folate is found naturally in a wide variety of food, especially in dark leafy vegetables (foliage), fruits, and animal products. The U.S. Food and Drug Administration (FDA) began requiring manufacturers to fortify enriched bread, cereals, flours, and cornmeal to increase the consumption of folate in the American diet. For the folate content of various foods, see Table 5.2.16.

Table 5.2.16: Folate Content of Various Foods

Dietary Supplement Fact Sheet: Folate. National Institute of Health, Office of Dietary Supplements. Updated April 20, 2016. Accessed October 22, 2017.

Vitamin B12 (Cobalamin)

Vitamin B12 contains cobalt, making it the only Vitamin with a metal ion. Vitamin B12 is bound to protein in food (Mahmood, 2014). In the stomach, hydrochloric acid releases Vitamin B12 from protein, combining with intrinsic factor (Mahmood, 2014). The Vitamin B12-intrinsic factor complex is absorbed through the intestinal enterocytes and enters circulation (Mahmood, 2014).

Vitamin B12 is an essential part of coenzymes. It is necessary for fat and protein catabolism, folate coenzyme function, and hemoglobin synthesis. A folate-dependent enzyme needs an enzyme requiring Vitamin B12 to synthesize DNA. Thus, a deficiency in Vitamin B12 has similar consequences to health as folate deficiency. In children and adults, Vitamin B12 deficiency causes macrocytic anemia. Pernicious anemia is caused by secondary intrinsic factor deficiency from loss of parietal cells, small intestine disorders, genetic mutations, or gastric surgery, which disrupts Vitamin B12 absorption (Mahmood, 2014). Red blood cells do not divide normally and are too large due to a Vitamin B12 deficiency (Maymood, 2014).  There is an increased risk for neural tube defects for babies born to cobalamin-deficient mothers. For the human body to absorb Vitamin B12, the stomach, pancreas, and small intestine must function properly.

Reversible symptoms of Vitamin B12 deficiency include feeling tired and weak, as the red blood cells in macrocytic anemia have a lower capacity to distribute oxygen to the body (Dietitians of Canada, 2019). Other irreversible symptoms include tingling/numbness in the limbs, motor and visual disturbances, and cognitive impairments such as memory loss and dementia (Stover, 2010). Vitamin B12 deficiency can be treated with oral Vitamin B12 supplements or intramuscular injections (Stover, 2010).

Vitamin B12 Relationship with Folate and Vitamin B6

Vitamin B12 and folate play key roles in converting homocysteine to amino acid methionine. As mentioned previously, high levels of homocysteine in the blood increase the risk of heart disease. Low levels of Vitamin B12, folate or Vitamin B6 will increase homocysteine levels, increasing the risk of heart disease.

When there is a deficiency in Vitamin B12, inactive folate (from food) cannot be converted to active folate and used in the body to synthesize DNA. Folic Acid, however (that comes from supplements or fortified foods), is available to be used as active folate in the body without Vitamin B12. Therefore, macrocytic anemia may occur if there is a deficiency in Vitamin B12. Fortifying foods with folate decreases the risk of an individual developing macrocytic anemia.

Dietary Reference Intakes of Vitamin B12

The RDAs and ULs for different age groups for Vitamin B12 are listed in Table 5.2.17.

Table 5.2.17: Dietary Reference Intakes for Vitamin B12 (mcg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of B12

Vitamin B12 is found naturally in animal products such as fish, meat, poultry, eggs, and milk products. Although Vitamin B12 is not generally present in plant foods, fortified breakfast cereals are also a good source of Vitamin B12. For the Vitamin B12 content of various foods, see Table 5.2.18.

Table 5.2.18: B12 Content of Various Foods

Source: Dietary Fact Sheet: Vitamin B12. National Institute of Health, Office of Dietary Supplements. Updated February 11, 2016. Accessed October 28, 2017.

Choline

Choline is a water-soluble substance that is not classified as a vitamin because the body can synthesize it. However, the synthesis of choline is limited and therefore it is recognized as an essential nutrient. Choline is needed to perform functions such as lipid transport, homocysteine metabolism, synthesizing the neurotransmitter acetylcholine, and phospholipids used to make cell membranes. A deficiency in choline may lead to impaired brain development in the fetus during pregnancy, and in adults can cause fatty liver and muscle damage.

Dietary Reference Intakes of Choline

There is insufficient data on choline, so the FNB has developed AIs for all ages to prevent fatty liver disease. The AI and UL for different age groups for choline are listed in Table 5.2.19.

Table 5.2.19: Adequate Intakes for Choline (mg/day) for adults over 19.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html

Dietary Sources of Choline

Choline can be found in a variety of different foods. The main dietary sources of choline in the United States consist of primarily animal-based products. For the Choline content of various foods, see Table 5.2.20.

Table 5.2.20: Choline Content of Various Foods

Source: Fact Sheet for Health Professionals: Choline. National Institute of Health, Office of Dietary Supplements. Updated January 25, 2017. Accessed October 28, 2017.

Summary of Water-Soluble Vitamins

A table that summarizes water-soluble vitamins.

Major minerals are classified as minerals that are required in the diet each day in amounts larger than 100 milligrams. These include sodium, potassium, chloride, calcium, phosphorus, magnesium, and sulfur. These major minerals can be found in various foods. For example, in Guam, the major mineral, calcium, is consumed in the diet not only through dairy, a common source of calcium, but also through the mixed dishes, desserts, and vegetables that they consume. A varied diet significantly improves an individual’s ability to meet nutrient needs (Pobocik, Trager & Monson, 2008).

Bioavailability

Minerals are not as efficiently absorbed as most vitamins, so minerals’ bioavailability can be very low. Plant-based foods often contain factors, such as oxalate and phytate, that bind to minerals and inhibit (interfere with) their absorption. In general, minerals are better absorbed from animal-based foods. In most cases, absorption will decrease if a particular mineral’s dietary intake is increased. Some minerals influence the absorption of others. For instance, excess zinc in the diet can impair iron and copper absorption. Conversely, certain vitamins enhance mineral absorption. For example, Vitamin C boosts iron absorption, and Vitamin D boosts calcium and magnesium absorption. As is the case with vitamins, certain gastrointestinal disorders, and diseases, such as Crohn’s disease and kidney disease, as well as the aging process, impair mineral absorption, putting people with malabsorption conditions and the elderly at higher risk for mineral deficiencies.

Calcium’s Functional Roles

Calcium is the most abundant mineral in the body, and over 99% of it is stored in bone tissue. Although only 1% of the calcium in the human body is found in the blood and soft tissues, it is here that it performs the most critical functions. Blood calcium levels are rigorously controlled so that if blood levels drop the body will rapidly respond by stimulating bone breakdown, thereby releasing stored calcium into the blood. Thus, bone tissue sacrifices its stored calcium to maintain blood calcium levels. Therefore, bone health depends on dietary calcium intake, and blood calcium levels do not always correspond to dietary intake.

Calcium plays a role in several different functions in the body. The most well-known calcium function is to build and strengthen bones and teeth. Recall that when bone tissue first forms during the modelling or remodelling process, it is unhardened, protein-rich tissue. In bone mineralization, calcium phosphates (salts) are deposited on the protein matrix. Calcium salts typically make up about 65% of bone tissue. When your diet is calcium deficient, the mineral content of bone decreases, causing it to become brittle and weak. Thus, increased calcium intake helps increase bone tissue’s mineralized content. Greater mineralized bone tissue corresponds to a greater bone mineral density (BMD) and greater bone strength. The remaining calcium plays a role in nerve impulse transmission by facilitating electrical impulse transmission from one nerve cell to another. Calcium in muscle cells is essential for muscle contraction because the flow of calcium ions is needed for the muscle proteins to interact. Calcium is also essential in blood clotting by activating clotting factors to fix damaged tissue.

In addition to calcium’s four primary functions, calcium has several other minor functions that are critical for maintaining normal physiology. For example, without calcium, the hormone insulin could not be released from cells in the pancreas, and glycogen could not be broken down in muscle cells and used to provide energy for muscle contraction.

Maintaining Calcium Levels

Because calcium performs such vital functions in the body, blood calcium level is closely regulated by the hormones parathyroid hormone (PTH), calcitriol, and calcitonin. PTH is secreted to increase blood calcium levels via three different mechanisms when blood calcium levels are low. First, PTH stimulates the release of calcium stored in the bone. Second, PTH acts on kidney cells to increase calcium reabsorption and decrease excretion in the urine. Third, PTH stimulates enzymes in the kidney that activate Vitamin D to calcitriol. Calcitriol is the active hormone that acts on the intestinal cells and increases dietary calcium absorption. When blood calcium levels become too high, the hormone calcitonin is secreted by cells in the thyroid gland and PTH secretion stops. At higher nonphysiological concentrations, calcitonin lowers blood calcium levels by increasing calcium excretion in the urine, preventing further absorption of calcium in the gut and directly inhibiting bone resorption (Birkett, 1998).

There are three possible routes of the parathyroid hormone when blood calcium levels are low. One is to stimulate the release of calcium from the bone to get to normal calcium levels. A second is the activation of Vitamin D which increases intestinal calcium absorption. The last route is to reduce the calcium lost in urine. These are all ways the body maintains calcium levels (Birkett, 1998).

Beware of Lead

There is public health concern about the lead content of some brands of calcium supplements, as supplements derived from natural sources such as oyster shell, bone meal, and dolomite (a type of rock containing calcium magnesium carbonate) are known to contain high amounts of lead. In one study conducted on twenty-two brands of calcium supplements, eight of the brands exceeded the acceptable limit for lead content. This was the case in supplements derived from oyster shells and refined calcium carbonate. The same study also found that brands claiming to be lead-free did show very low lead levels. Because lead levels in supplements are not disclosed on labels, it is important to know that products not derived from an oyster shell or other natural substances are generally low in lead content. In addition, it was also found that one brand did not disintegrate as is necessary for absorption, and one brand contained only 77 percent of the stated calcium content (Ross et al., 2000).

Diet, Supplements, and Chelated Supplements

In general, calcium supplements do not perform as well as dietary sources of calcium in providing many of the health benefits linked to higher calcium intake. This is partly because dietary sources of calcium supply additional nutrients with health-promoting activities. Chelated forms of calcium supplements are easier to absorb as the chelation process protects the calcium from oxalates and phytates that may bind with the calcium in the intestines. However, these are more expensive supplements and only increase calcium absorption by up to 10 percent. In people with low dietary intakes of calcium, calcium supplements have a negligible benefit on bone health without Vitamin D – Vitamin D must be activated and, in the bloodstream, promote calcium absorption. Thus, it is important to maintain an adequate Vitamin D intake for optimal calcium utilization. Limiting calcium supplementation and striving to get most of your calcium from food is best.

Dietary Reference Intake for Calcium

The recommended dietary allowances (RDAs) for calcium are listed in Table 5.3.1. The RDAs are higher for women above age fifty and men older than seventy-one, because as we age, calcium absorption in the gut decreases, Vitamin D3 activation is reduced, and maintaining adequate blood calcium levels is important to prevent accelerating bone tissue loss (especially during menopause). Currently, the dietary intake of calcium for females above age nine is, on average, below the R.D.A. for calcium. The Institute of Medicine (IOM) recommends that people not consume over 2,500 milligrams per day of calcium as it may cause adverse effects in some people.

Table 5.3.1: Dietary Reference Intakes for Calcium (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Dietary Sources of Calcium

In the typical Canadian diet, calcium is obtained mostly from dairy products, primarily cheese. A slice of cheddar or Swiss cheese contains just over 200 milligrams of calcium. One cup of nonfat milk contains approximately 300 milligrams of calcium, which is about a third of the RDA for calcium for most adults. Foods fortified with calcium, such as cereals, soy milk, and orange juice also provide one-third or greater of the calcium RDA. Although the typical American diet relies primarily on dairy products for obtaining calcium, there are other good non-dairy sources of calcium.

Tools For Change

If you need to increase calcium intake, are a vegan, or have a food allergy to dairy products, it is helpful to know that some plant-based foods are high in calcium. Tofu (made with calcium sulfate), turnip greens, mustard greens, and Chinese cabbage are good sources. For a list of non-dairy sources, you can find the calcium content for thousands of foods by visiting the USDA National Nutrient Database. When obtaining calcium from a vegan diet, it is important to know that some plant-based foods significantly impair calcium absorption. These include spinach, Swiss chard, rhubarb, beets, cashews, and peanuts. Careful planning and good selections can provide sufficient calcium for those who do not consume milk or dairy products. Table 5.3.2 shows the calcium content of various foods.

Table 5.3.2: Calcium Content of Various Foods

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Dietary Sources of Phosphorus

Table 5.3.4: Phosphorus Content of Various Foods

Micronutrient Information Center: Phosphorus. Oregon State University, Linus Pauling Institute. Updated on June 2014. Accessed June 30, 2019.

Contributors

University of Hawai’i at Mānoa Food Science and Human Nutrition Program: Allison Calabrese, Cheryl Gibby, Billy Meinke, Marie Kainoa Fialkowski Revilla, and Alan Titchenal

Magnesium

Many Canadians do not get the recommended intake of magnesium from their diets. Some observational studies suggest mild magnesium deficiency is linked to increased risk for cardiovascular disease. Signs and symptoms of severe magnesium deficiency may include tremor, muscle spasms, loss of appetite, and nausea.

1 Tucker KL, Hannan MT, et al. Potassium, Magnesium, and Fruit and Vegetable Intakes Are Associated with Greater Bone Mineral Density in Elderly Men and Women. Am J Clin Nutr. 1999; 69(4), 727–36. Accessed June 30, 2019.

Dietary Reference Intake and Food Sources for Magnesium

The RDAs for magnesium for adults between ages nineteen and thirty are 400 milligrams per day for males and 310 milligrams per day for females. For adults above age thirty, the RDA increases slightly to 420 milligrams per day for males and 320 milligrams for females. Table 5.3.5 shows the RDA for magnesium.

Table 5.3.5: Dietary Reference Intakes for Magnesium (mg/day) for adolescents and adults.

*The UL is based on supplemental magnesium, not magnesium from food.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Dietary Sources of Magnesium

Magnesium is part of the green pigment, chlorophyll, vital for photosynthesis in plants; therefore, green leafy vegetables are good dietary sources for magnesium. Magnesium is also found in high concentrations in fish, dairy products, meats, whole grains, and nuts. Additionally, chocolate, coffee, and hard water contain a good amount of magnesium. Most people in America do not fulfill the RDA for magnesium in their diets. Typically, Western diets have a low fish intake and predominantly include refined grains rather than whole grains. Table 5.3.6 shows the magnesium content of various foods.

Table 5.3.6: Magnesium Content of Various Foods

Source: Dietary Supplement Fact Sheet: Magnesium. National Institutes of Health, Office of Dietary Supplements. Updated September 26, 2018. Accessed June 30, 2019.

Contributors

University of Hawai’i at Mānoa Food Science and Human Nutrition Program: Allison Calabrese, Cheryl Gibby, Billy Meinke, Marie Kainoa Fialkowski Revilla, and Alan Titchenal

Sodium

Table salt is approximately 40 percent sodium and 60 percent chloride. As a reference point, just ⅔ teaspoon of salt is needed in the diet to meet the AI for sodium. The AI considers the amount of sodium lost in sweat during recommended physical activity levels and additionally provides for the sufficient intake of other nutrients, such as chloride. Sodium deficiency is not a concern, and higher intakes are associated with an increased risk of chronic disease, especially blood pressure. The Tolerable Upper Intake Level (UL) for sodium is not determined; however, it is recommended to reduce intakes to below 2,300 milligrams per day for adults, especially if a person has hypertension. Just over 1 teaspoon of salt contains 2,300 milligrams of sodium. Table 5.3.7 shows the AI for sodium.

Table 5.3.7: Adequate Intakes for Sodium (mg/day) for adolescents and adults.

Source: Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate. Institute of Medicine. http://www.iom.edu/Reports/2004/Dietary-Reference-Intakes-Water-Potassium-Sodium-Chloride-and-Sulfate.aspx. Updated February 11, 2004. Accessed September 22, 2017.

Food Sources for Sodium

Most sodium in the typical North American diet comes from processed and prepared foods. Manufacturers add salt to foods as a preservative and to improve texture and flavour. The amount of salt in similar food products varies widely. Some foods, such as meat, poultry, and dairy foods, contain naturally occurring sodium. For example, one cup of low-fat milk contains 107 milligrams of sodium. Naturally occurring sodium accounts for less than 12 percent of dietary intake in a typical diet. For the sodium contents of various foods see Table 5.3.8.

Table 5.3.8: Sodium Contents of Selected Foods.

Sodium on the Nutrition Facts Panel

Sodium level in milligrams is a required listing on a Nutrition Facts label.

Tools for Change

To decrease your sodium intake, become a salt-savvy shopper by reading the label and the ingredient list of processed foods and choosing those lower in salt. Even better, stay away from processed foods and control the seasoning food with salt-based seasoning. Reducing salty foods diminishes salt cravings, so you may need to try a lower sodium diet for a week or two before you will be satisfied with the less salty food. If you have been diagnosed with hypertension, consider following the D.A.S.H. diet.

Salt Substitutes

Using a salt substitute is an option for those looking to decrease salt use. However, many salt substitutes still contain sodium, just in lesser amounts than table salt. Also, remember that most salt in the diet is from proccessed foods, not from table salt. Salt substitutes often replace sodium with potassium. People with kidney disorders often have problems excreting excess potassium and are advised to avoid salt substitutes containing potassium. People with liver disorders should also avoid salt substitutes containing potassium because their treatment is often accompanied by potassium dysregulation. Table 5.3.9 contains a list of low-sodium seasonings.

Table 5.3.9: Salt Alternatives.

Needs and Dietary Sources of Potassium

Table 5.3.10: Adequate Intake of Potassium(mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Food Sources for Potassium

Fruits and vegetables that contain high amounts of potassium are spinach, lettuce, broccoli, peas, tomatoes, potatoes, bananas, apples, and apricots. Whole grains, seeds, certain fish (such as salmon, cod, and flounder), and meats are also high in potassium. The Dietary Approach to Stop Hypertension (DASH diet) emphasizes potassium-rich foods.

Table 5.3.9: Potassium Contents of Selected Foods.

Bioavailability

Greater than 90 percent of dietary potassium is absorbed in the small intestine. Although highly bioavailable, potassium is a very soluble mineral and is easily lost during the cooking and processing of foods. Fresh and frozen foods are better sources of potassium than canned.

Contributors

Table 5.4.2: Enhancers and Inhibitors of Iron Absorption

 Iron Toxicity

The body excretes little iron, so the potential for accumulation in tissues and organs is considerable. Iron accumulation in tissues and organs can cause many health problems in children and adults, including extreme fatigue, arthritis, joint pain, and severe liver and heart toxicity. In children, death has occurred from ingesting as little as 200 mg of iron; therefore, it is critical to keep iron supplements out of children’s reach. The IOM has set tolerable upper intake levels of iron (Table 5.4.3). Hemochromatosis, a hereditary disease, leads to abnormal iron metabolism and an accumulation of iron in certain tissues such as the liver, pancreas, and heart. The signs and symptoms of hemochromatosis are similar to iron overload in tissues caused by high dietary intake of iron or other non-genetic metabolic abnormalities but are often increased in severity. Table 5.4.4 shows the iron content of various foods.

Dietary Reference Intakes for Iron

Table 5.4.3: Dietary Reference Intakes for Iron (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Dietary Sources of Iron

Table 5.4.4: Iron Content of Various Foods.

Contributors

Table 5.4.5: Dietary Reference Intakes for Zinc (mg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Dietary Sources of Zinc

Table 5.4.6: Zinc Content of Various Foods

Fact Sheet for Health Professionals: Zinc. National Institute of Health, Office of Dietary Supplements. Updated March 13, 2019. Accessed July 5, 2019.

Contributors

University of Hawai’i at Mānoa Food Science and Human Nutrition Program: Allison Calabrese, Cheryl Gibby, Billy Meinke, Marie Kainoa Fialkowski Revilla, and Alan Titchenal

Selenium

Selenium has many roles in the body. It plays a role in reproduction, is a cofactor in thyroid metabolism, is involved with DNA synthesis, and acts as an antioxidant, protecting the body from Reactive Oxygen Species (ROS). Reactive oxygen species (ROS) are generated from mitochondrial metabolism and in response to bacterial invasion, among other things. Common ROS include superoxide and hydrogen peroxide. Left unchecked, ROS can cause oxidative damage to DNA, proteins and lipids in membranes. Glutathione peroxidase-1 is a selenium-containing intercellular enzyme that breaks down ROS hydrogen, protecting the body from oxidative damage.

Selenium and Cancer

As an antioxidant, it was thought that selenium may play a role in preventing cancer. A systematic review of selenium’s role in preventing cancer concluded that selenium had no effect in reducing the overall risk of cancer, including prostate cancer, and some trials showed an increased risk of high-grade prostate cancer, type 2 diabetes, and dermatological abnormalities (Vinceti et al., 2018; Benstoem et al., 2015).

Dietary Reference Intakes for Selenium

The IOM has set the RDAs for selenium based on the amount required to maximize the activity of glutathione peroxidases found in blood plasma. The RDAs for different age groups are listed in Table 5.4.7. Food sources of selenium are found in Table 5.4.8.

Table 5.4.7: Dietary Reference Intakes for Selenium (mcg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Selenium at doses several thousand times the RDA can cause acute toxicity, and, when ingested in gram quantities can be fatal. Chronic exposure to foods grown in soils containing high levels of selenium (significantly above the UL) can cause brittle hair and nails, gastrointestinal discomfort, skin rashes, halitosis, fatigue, and irritability. The IOM has set the UL for selenium for adults at 400 micrograms per day.

Table 5.4.8: Selenium Content of Various Foods

Source: US Department of Agriculture, Agricultural Research Service. 2010. USDA National Nutrient Database for Standard Reference, Release 23.

Contributors

University of Hawai’i at Mānoa Food Science and Human Nutrition Program: Allison Calabrese, Cheryl Gibby, Billy Meinke, Marie Kainoa Fialkowski Revilla, and Alan Titchenal

Iodine

Table 5.4.9: Dietary Refernce Intakes for Iodine (mcg/day) for adolescents and adults.

Source: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html

Table 5.4.10: Iodine Content of Various Foods.