Originally published in The Ottawa Citizen December 16, 2003
Original Title: The vitals on vitamins – Part 2
What do some of the B vitamins and antioxidants do? Are we dealing with marketing hype?
Vitamin B6 (pyridoxine), found in whole grains, dried beans, eggs and nuts, is involved in the normal functioning of the central nervous system and in the production of red blood cells. It works in conjunction with folate and B12 to reduce homocysteine levels.
Vitamin B2 (riboflavin) and B3 (niacin) aid in the release of energy from foods and each interacts with other B vitamins. Nuts, dairy products, fortified cereal and liver are good sources. Niacin helps in the synthesis of DNA and maintains normal functioning of the skin, nerves and digestive system.
Vitamin B12 (cyanocobalamin) is found in liver, beef, eggs, milk and shellfish. Vitamin B12 deficiency is commonly seen in patients with poor diets, vegans, alcoholics and people with various intestinal diseases. Unlike many other foods and minerals, a special substance called intrinsic factor aids in B12‘s absorption in a specific area of the small intestine called the terminal ileum. The elderly tend to produce less intrinsic factor. Surgical resection of the terminal ileum will impair B12 absorption.
B12 deficiency will cause nervous system damage and megaloblastic anemia. It is the only water-soluble vitamin that is stored in the body. The liver has the potential to store about five years worth.
A number of studies looked at the potential of antioxidant vitamins, A, C, E and betacarotene in the prevention of cancer and heart disease. Antioxidants neutralize electrically charged chemical compounds called free radicals. Free radicals, like ozone and cigarette smoke byproducts, destroy normal tissue through a process called oxidation. It is the same process that causes rust.
Citrus fruits, strawberries and tomatoes are a good source of vitamin C (ascorbic acid). This vitamin helps maintain the growth and integrity of connective tissue throughout the body. It promotes healthy blood vessels, gums and teeth and aids in wound healing. Several long-term studies looking into cancer, stroke and heart disease prevention with vitamin C are inconclusive.
Observational studies tend to show that diets high in vegetables and fruits (that are rich in antioxidant vitamins) are associated with a reduced risk of cancer and cardiovascular disease. However, this effect may be due to the antioxidants, some other compound in the fruits or vegetables such as flavonoids or meat and fat reductions within the diet. A person’s genetic potential for cancer or conversely his/her response to antioxidant vitamins is also a consideration.
Vitamin A promotes good vision and maintains healthy skin and mucous membranes. Retinol is the active form of vitamin A (preformed vitamin A). It is found in animal products and supplements.
Beta-carotene is found in fruits (cantaloupe and apricots) and in vegetables (carrots and tomatoes). The body will convert it into retinol.
Cancer, stroke and heart disease prevention studies using vitamin A failed to demonstrate any benefit. Indeed in some lung and prostate cancer studies, the rate of cancer incidence increased. Beta-carotene supplement use should be discouraged because of its potential side effects and lack of clinical effect.
Studies noted that Vitamin A did improve the immunity status of children living in developing countries. The World Health Organization recommends supplementation at the community level because of the supporting evidence.
Women should avoid supplements with greater than 5000 units of vitamin and high dietary intake of preformed vitamin A found in foods such as liver, milk, egg yolk, and butter because of a possible increased risk of hip fractures in women especially those with low bone calcium content (osteopenia).
A notable exception is vitamin A in pregnancy which can cause birth defects at doses as low as several times the recommended daily allowance.
Vitamin E (alpha-tocopherol) is found in nuts, vegetable oils, whole grains, olives, asparagus and spinach. It helps in the production of red blood cells and helps the body use vitamin K. Vitamin K aids in blood clotting.
Although there is some evidence to support vitamin E’s ability to prevent aggressive prostate and lung cancer in smokers, it is not conclusive. Nearly all randomized trials have shown no benefit preventing coronary heart disease and stroke. Other studies indicate it does not improve immune system function.
Studies are ongoing to look at vitamin E’s effect upon the development of dementia and Alzheimer’s disease. Early data is encouraging but not enough to make any general recommendations.
The benefits of vitamin supplements remain a question mark. There is little evidence to support vitamin megadosing. Indeed, there are potential adverse interactions with prescription medication like anti-coagulants.
It is our diet rather than the vitamin supplements that has the greater impact on health. A diet with five or more servings of different colour vegetables, legumes and fruits per day will provide a wide range of vitamins, fibre and trace nutrients and will replace some meat and animal fat. It is and always has been about balance and moderation.