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Leslie Beck's Q and A on anti-oxidants

Leslie Beck, Canada AM nutrition expert
Published Wednesday, November 12, 2008 8:21AM EST Last Updated Friday, May 18, 2012 9:30PM EDT

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Question: Tell us more about this new study...

In today's study, called the Physicians' Health Study II, researchers from Harvard Medical School assigned 14,461 healthy men, aged 50 and older, to take either 400 international units (IU) of vitamin E every other day, 500 milligrams of vitamin C daily, or a placebo pill.

Antioxidants such as vitamins C, E, selenium and beta carotene are thought to thwart damage caused by free radicals, highly reactive oxygen molecules that harm cells thereby boosting the risk of cancer and other diseases. Antioxidants are also thought to slow or prevent the build-up of fatty plaques in arteries by preventing damage to LDL cholesterol by free radicals.

After eight years, neither supplement lowered the risk of cardiovascular disease. Compared to men taking the placebo treatment, vitamin E and vitamin C users were just as likely to suffer a heart attack, total stroke, or die from heart disease.

This study did find a significantly higher risk of hemorrhagic stroke among vitamin E users. (A hemorrhagic stroke is caused by a weakened blood vessel that ruptures and bleeds into the brain.) No harmful side effects were observed for vitamin C.

Question: If not heart disease, can antioxidant supplements help prevent cancer?

There's no evidence that antioxidant supplements reduce the risk of cancer. A report published earlier this year concluded after analyzing 67 studies that overall, popping an antioxidant supplement didn't reduce the risk of dying from any cause in healthy people or patients who were sick.

And last month, after researchers from the Cleveland Clinic discovered that selenium and vitamin E pills did nothing to ward off prostate cancer - and may even increase risk of the disease - they instructed the study participants to stop taking their supplements. This randomized controlled trial, called SELECT, gave 35,000 men, aged 50 and older, vitamin E (400 IU) and selenium (200 micrograms) together, vitamin E alone, selenium alone, or placebo.

The early analysis also revealed two worrisome trends: a small increase in the number of prostate cancers among vitamin E users and a small rise in type-2 diabetes among those taking selenium. Neither finding was statistically significant, meaning it could be a coincidence.

Question: What about multivitamins - are they safe to take?

Yes, standard multivitamins containing antioxidants in low doses are considered safe provided you take only one per day, although they have not been proven to guard against cancer or heart disease. I certainly think it is wise to take 1000 IU of vitamin D each day to help reduce the risk of certain cancers such as breast, colon and prostate.

Question: Is it best to get your antioxidants from food?

In my opinion, yes. Research has linked diets high in antioxidant-rich foods to a lower risk of heart attack and certain cancers. Getting your antioxidants from foods also means you're consuming protective phytochemicals, fibre, and other vitamins and minerals - all of which likely work together to combat disease.

Question: What are the best food sources?