There's little argument that a healthy diet helps fight disease. Large studies have consistently shown that a diet based on whole grains, fruits, vegetables, legumes and vegetable oils helps prevent high blood pressure, heart disease, stroke, osteoporosis, Type 2 diabetes and certain cancers.
If your diet is less than stellar, you might be inclined to reach for a supplement to fill the gaps. According to Statistics Canada, nearly half (42 per cent) of Canadian adults have taken a vitamin and mineral supplement in the past month.
But depending on which supplement you choose - and how much you take - you might be doing more harm than good.
As I wrote in last week's column, there's little, if any, evidence that antioxidant supplements - vitamins C and E, beta carotene and selenium - ward off heart disease or cancer. What's more, there's some suggestion that high doses of vitamin E and beta carotene can be dangerous for certain people.
Antioxidants are not the only supplements that have been called into question. Recent reports have questioned the safety of multivitamins and folic acid - supplements routinely recommended by the medical community, myself included.
When it comes to multivitamins, most people who pop one a day do so as a form of health insurance. Yet there's no evidence that taking a one-a-day formula will prevent future disease.
A 2006 review conducted by the U.S. National Institutes of Health found too few studies to give multivitamins a go-ahead for heart disease and cancer prevention. Despite the lack of evidence for benefit or harm, it's still prudent for some segments of the population to reach for a multivitamin to fill nutritional gaps.
There is clear evidence that taking a multivitamin with 400 micrograms of folic acid (a B vitamin) before and during pregnancy prevents neural tube defects, birth defects that affect the brain and spinal cord.
When it comes to iron, it's challenging for menstruating women to meet their daily requirement (18 milligrams) from food alone. This is especially true for vegetarians and women who follow a low-calorie diet.
With age, we have more difficulty absorbing vitamin B12 from food. That's why the U.S. Institute of Medicine advises adults over 50 to get the nutrient from a supplement or fortified foods (e.g. soy beverages).
Vitamin B12 is found only in animal foods, so strict vegetarians must also rely on a multivitamin to meet their daily needs.
A multivitamin can provide a safety net if you don't get your full complement of nutrients from diet. And despite good intentions, not all of us follow Canada's Food Guide to the letter. Stress, workplace demands and lack of time and energy are common barriers to eating healthfully.
But more is not better. A 2007 study published in the Journal of the National Cancer Institute found that taking a multivitamin more than seven times per week was linked with a greater risk of advanced prostate cancer and risk of death from the disease.
The link was strongest in men with a family history of prostate cancer and in men who also took zinc, selenium or beta carotene supplements. Regular multivitamin use (no more than once daily) did not boost prostate cancer risk. (The researchers were unable to determine which ingredient was responsible for the association.)
There's also some concern that high doses of folic acid, a B vitamin thought to guard against colon and breast cancer, might do more harm than good.
In a recent trial of 1,021 men and women who had had precancerous polyps removed from their colons, those who took a folic acid supplement (1 milligram) got just as many new polyps as those who took placebo pills. And people in the folic acid group had higher rates of advanced tumours and multiple tumours, although this could have been a chance finding. The result raised the possibility that if taken early, folic acid may prevent polyps from forming in the first place, but if taken once they're formed it may accelerate their growth.
When used sensibly and safely, the following strategies can help meet daily nutrient needs - and possibly reduce your risk of future disease.
EAT A HEALTHFUL DIET
No vitamin pill can make up for a diet that's laden in saturated and trans fats, refined sugars and sodium. Nor can a supplement offer the hundreds of naturally occurring plant chemicals thought to improve health. Ensure your daily diet includes whole grains, fruits and vegetables to get a mix of disease-fighting nutrients and phytochemicals.
TAKE A MULTIVITAMIN
WITH MINERALS
Choose a standard one-a-day formula that offers 100 per cent of the recommended daily intake for most nutrients. Men, in particular, should avoid "mega" or "super" formulas that can contain high amounts of zinc, selenium and/or beta carotene.
ADD EXTRA CALCIUM
Many studies have demonstrated that calcium increases bone density in postmenopausal women. In conjunction with vitamin D, calcium also reduces the risk of hip fracture.
Adults aged 19 to 50 need 1,000 milligrams of calcium, while older adults should consume 1,500 mg each day. If your diet falls short, increase intake from foods or take a supplement. (A 250-millilitre serving of milk, yogurt or soy beverage provides about 300 mg of calcium.) Spread your calcium intake over the course of the day. Absorption from supplements is best in doses of 500 mg or less, taken with meals.
TAKE VITAMIN D
To help guard against cancer, the Canadian Cancer Society suggests taking 1,000 IU (international units) of vitamin D in the fall and winter, and year-round if you're over 50, have dark skin, don't go outdoors often or wear clothing that covers most of your skin.
Evidence also suggests that vitamin D helps prevent heart attack, stroke and heart failure.
Before you buy, figure out how much vitamin D you're already getting from your multivitamin and calcium supplements. Choose a supplement that contains D3 instead of D2, which is less potent.
Leslie Beck, a Toronto-based
dietitian at the Medcan Clinic,
is on CTV's Canada AM
every Wednesday. Her website
is lesliebeck.com.
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Multivitamin checklist
Vitamins
Look for A, C, D, E, B1, B2, niacin, B6, folic acid and B12. Choose a formula that provides 100 per cent of the recommended daily allowance for B6 (1.3 to 1.7 milligrams), B12 (2.4 micrograms) and folic acid (400 mcg).
Avoid products that supply more than 2,500 IU (international units) of vitamin A from retinol (often called vitamin A palmitate or acetate). Excess vitamin A may increase the risk of osteoporosis and hip fracture.
If you take prescription anticoagulants, or blood thinners such as Coumadin, speak to your doctor before taking a formula with vitamin K.
Minerals
Look for chromium, copper, iron, magnesium, selenium and zinc.
Pre-menopausal women should choose a multivitamin with 10 to 18 mg of iron; postmenopausal women and men should look for no more than 5 to 10 mg of iron.
If your diet lacks calcium, you'll need a separate supplement since the recommended daily amount is too large to fit into a multivitamin pill.
Leslie Beck
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