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Antioxidants, widely touted to ward off heart attacks, cancer, even Alzheimer's disease, were once again called into question last week.

A review of 67 randomized controlled studies concluded that antioxidant supplements do not extend life and some - vitamins A and E and beta carotene - could even cause premature death.

Antioxidant nutrients such as vitamins C and E, beta carotene and selenium are thought to help counter damage caused by free radicals, unstable oxygen molecules that can harm cells and lead to chronic disease.

While numerous studies have linked diets high in antioxidant-rich fruits and vegetables to a lower risk of heart attack, stroke, high blood pressure, certain cancers and vision loss, clinical trials using supplements of antioxidants have yielded mixed results with most not finding desired benefits.

The latest report, published by the Cochrane Collaboration, an international organization that evaluates medical research, pooled the results of studies involving 232,550 participants who were assigned one or a combination of antioxidant supplements compared with placebo. Twenty-one trials were conducted on healthy people; 46 included people with various diseases.

Over all, antioxidant supplements did not reduce the risk of dying from all causes in healthy people or in patients who were sick.

When the researchers accounted for various factors and excluded certain trials, vitamin A, beta carotene and vitamin E supplements were linked with harm - a 16-, 7- and 4-per-cent increased risk of dying respectively. Vitamin C and selenium had no effect one way or the other. (The researchers did not determine the cause of death; cancer and heart disease are assumed to be the main reasons for increased mortality.)

The researchers speculated that antioxidant supplements may interfere with how the body defends itself from disease.

This latest report is not without criticism. Experts questioned why the reviewers included only studies in which someone died; 405 death-free trials were excluded from the analysis. Among the studies that were included, most looked at the effect of antioxidant supplements in people with existing disease, rather than healthy populations. (It's possible that antioxidant nutrients may be beneficial before disease has been established.)

Critics also felt the studies reviewed were too different to be pooled together. Others raised concerns about the use of "all-cause mortality" as a measure of antioxidants' influence on health.

This isn't the first time antioxidants have endured bad news. The first hint that antioxidants could pose harm came from two studies conducted in male smokers, therefore at high risk for lung cancer. In both studies, men who took beta carotene supplements had a significant increase in lung cancer risk compared with those taking a placebo. (A beta carotene study in healthy male non-smokers did not find an increase in lung cancer.)

In 2005, a study in the Journal of the American Medical Association revealed that 400 international units of vitamin E did not lower heart or cancer risk in people with cardiovascular disease or diabetes. Worse, vitamin E pills were linked with a 13 per cent greater risk of heart failure, a condition in which the heart's ability to pump blood is weakened.

Another study from France found that a daily antioxidant supplement of vitamins C or E, beta-carotene, selenium and zinc guarded against cancer in men, but not in women.

I don't recommend antioxidant supplements to my clients. That's not because I believe they increase a person's risk of dying. Rather, there's little evidence that they protect against heart disease, stroke or cancer. Most studies conducted in healthy people show no benefit from taking vitamin E, vitamin C and/or beta carotene supplements.

There is one exception: A supplement containing beta carotene, vitamin C, vitamin E and zinc has been shown to reduce the risk of advanced age-related macular degeneration and its associated vision loss in people at high risk for the condition (people with intermediate AMD, or advanced AMD in one eye but not the other eye). The leading cause of severe vision loss in older adults, AMD attacks the central part of the retina, the macula, which controls fine, detailed vision.

I'm not against taking supplements. I think there's good evidence to warrant taking a multivitamin, vitamin D and fish oil. But when it comes to antioxidants and disease prevention, food is where it's at.

Plenty of evidence suggests you're better off getting your antioxidants from fruits, vegetables, whole grains, nuts and seeds. It's possible that antioxidant supplements haven't panned out because it takes a network of antioxidants in foods - not single antioxidants in pills - to combat free radicals and prevent disease.

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

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A healthy dose of antioxidants

VITAMIN C

The recommended daily intake is 75 milligrams for women; 90 milligrams for men. Smokers need an additional 35 mg. Safe daily upper limit*: 2,000 milligrams.

Best food sources: citrus fruit, citrus juices, kiwi, mango, cantaloupe, strawberries, broccoli, Brussels sprouts, red peppers, tomato juice.

VITAMIN E

The recommended daily intake for adults is 15 milligrams of alpha-tocopherol, equivalent to 22 international units of natural source or 33 IU synthetic vitamin E. Safe daily upper limit: 1,500 IU natural source or 1,100 IU synthetic vitamin E. People with heart disease and diabetes are advised to consult their doctor before taking 400 IU or more a day.

Best food sources: vegetable oils, sunflower seeds, almonds, hazelnuts, peanuts, kale.

BETA CAROTENE

There is no recommended daily intake for beta carotene. Research suggests that consuming three to six milligrams daily will maintain blood levels of beta carotene in the range linked with disease prevention.

Best food sources: carrots, winter squash, sweet potato, kale, spinach, turnip greens, collard greens, romaine lettuce, broccoli, apricots, cantaloupe, peaches, nectarines, mango, papaya.

SELENIUM

Adults need 55 micrograms of selenium a day. Safe daily upper limit: 400 micrograms

Best food sources: Brazil nuts, seafood, tuna, cod, beef, turkey breast, chicken breast.

*The safe daily upper limit is the highest level of intake that's likely to pose no risk of adverse health effects for most people.

Leslie Beck