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Calls by scientists to increase vitamin D intake have been getting louder over the last few years, making it the latest in a line of vitamins touted as a cancer preventive.

Last week, the Canadian Cancer Society heeded those calls. With a new study showing that vitamin D supplementation reduced the risk of cancer in women, the group recommended that adults "consider" taking 1,000 IU, or international units, of vitamin D daily in the fall and winter.

In the four-year study of 1,179 postmenopausal women published in the American Journal of Clinical Nutrition, researchers found that those taking 1,110 IU of vitamin D a day were 60 per cent less likely to get cancer than their peers taking placebos. The women took vitamin D along with calcium.

Earlier studies suggested that the vitamin protects from breast, colorectal, lung and prostate cancers as well as diabetes, multiple sclerosis and rheumatoid arthritis. But the recent study is the first randomized, controlled trial - the most reliable form of clinical evidence - to substantiate that vitamin D is an important tool in fighting cancer.

This isn't the first time scientists have deemed certain vitamins a safe and inexpensive measure to fight a myriad of illnesses and conditions. Antioxidants, folic acid and calcium have been hyped as potential disease fighters. But some of these much-touted nutrients have lost their lustre when further studies found no benefits, or worse, pointed to health risks. Which supplements are beneficial and which ones are potentially harmful?

Antioxidants

Antioxidant-rich diets have been linked in studies with better health outcomes, leading to the use of antioxidant supplements to prevent heart disease, cancer, cataracts, even Alzheimer's. The theory: Antioxidants such as vitamins C and E and beta-carotene destroy free radicals, unstable oxygen molecules that can damage cells and promote disease.

But randomized controlled trials failed to find benefits and some even suggested that antioxidant supplements can do harm. Two studies conducted in men at high risk for lung cancer found that beta-carotene supplements increased, rather than decreased, lung cancer risk.

Vitamin E, once widely used to ward off heart attacks and other ailments, also came under scrutiny when a 2005 study found that individuals who took 400 IU or more of the vitamin a day were six per cent more likely to die than those who didn't take supplements.

Folic acid

The evidence is clear that a daily supplement of folic acid reduces the risk of serious spinal cord birth defects. Folic acid has also been hyped as preventing cardiovascular disease and cancer, but whether this B vitamin offers such protection remains unclear.

An analysis of 12 trials, published last year, concluded the vitamin had no effect on heart disease or stroke risk. However, a study published in last week's issue of The Lancet concluded that people could cut their risk of stroke by 30 per cent by boosting their folic acid intake.

Observational studies have also linked higher intakes of folic acid with a lower risk of colon cancer. But according to a report published this month in the Journal of the American Medical Association, folic acid supplements may actually aggravate colorectal tumours.

Calcium

Faithful calcium users were bound to be confused last year when a study of 36,282 postmenopausal women found that standard calcium and vitamin D supplements had no effect on preventing bone fractures. But when the results were analyzed only for women who were most compliant with their calcium pills, the risk of hip fracture was reduced by 29 per cent compared to the placebo group.

All of this makes it hard to keep up with what we're supposed to take at what age, and in what dose. Based on the accumulation of evidence, it seems prudent to take a daily vitamin D supplement. The balance of evidence supports the need for higher vitamin D intakes, and 1,000 IU is a safe starting point.

Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday.

The 'sunshine vitamin' for young and old

Use the following guide to

determine which other supplements might help bolster your diet.

Infants

To reduce the risk of vitamin D deficiency and rickets, babies who are exclusively breastfed should receive a daily vitamin D supplement of 400 IU from birth until they get enough from their diet.

Babies living in northern communities (north of 55 degrees latitude) should get 800 IU a day.

Children and teens

If your child is a picky eater, a vegetarian or has food allergies, consider giving them a child's multivitamin (formulated for kids aged two to 12).

Menstruating girls, vegetarians and children who don't like meat should take a formula with iron.

During the teen years, daily requirements for most nutrients should increase to match - and in some cases exceed - adult levels. That's the time switch to a basic adult formula.

Depending on your child's diet, a calcium supplement may be needed.

Children aged one to three need 500 milligrams of calcium a day, four- to eight-year-olds need 800 mg and those aged nine to 18 require 1,300 mg. (250 millilitres of milk, 175 ml of yogurt, 45 grams of cheese and 250 ml of calcium-enriched soy beverage all supply roughly 300 mg of calcium.)

All adults

Take 1,000 IU of vitamin D in the fall and winter. Older adults, people with dark skin, those who don't go outdoors often and those who wear clothing that covers most of their skin should take the supplement all year round.

Before you buy, figure out how much vitamin D you're already getting from your multivitamin and calcium supplements.

Also, choose a supplement than contains vitamin D-3, a form that is more available to your body.

Women of childbearing age

Take a multivitamin and mineral to ensure a daily intake of 400 micrograms of folic acid. Choose a formula with 10 to 18 milligrams of iron.

Women need 1,000 milligrams of calcium; if your diet lacks calcium, reach for a supplement.

Older adults

To get adequate vitamin B12, males and females over 50 should take a multivitamin. Choose one with five to 10 milligrams of iron.

Older adults need 1,500 mg of calcium a day.

Unless you drink five cups (1¼litres) of milk each day, you'll need a calcium supplement once or twice daily.

Leslie Beck