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.
