Project Syndicate - NIS, Serbia – The influence of diet on health has been known since the Ancient Greeks. Our bodies simply cannot synthesize many essential compounds, so our health partly depends on what we eat and drink.Antioxidants, which are believed to help protect us against both cancer and heart disease, are one such element that must import into our bodies. Studies have shown that there is a significant positive association between a higher intake of fruits and vegetables and reduced risk of chronic disease.

Fruits and vegetables are sources of numerous micronutrients, and some, including b-carotene (a precursor of vitamin A), vitamin C, vitamin E, and selenium, have potential as antioxidants. But what specifically makes fruits and vegetables so beneficial is not clear.

The main role of antioxidants is to prevent oxidative damage to cellular components, so it has been proposed that dietary antioxidants decrease such damage and with it the risk of disease. This has stimulated interest in the possible preventive potential of antioxidant supplements.

Indeed, consumption of antioxidant supplements in developed countries has become widespread. More than one-third of adults in developed countries now ingest antioxidant pills, which is much easier than eating fruits and vegetables. But will the benefits be the same?

As with any therapeutic intervention, the most convincing and direct proof of the preventive efficacy of antioxidant supplements requires randomized, controlled clinical trials. Such trials eliminate the problems of participants’ dietary record and controls the effects of both known and unknown confounding factors.

So far, many studies have been conducted to verify the supposed beneficial effects of antioxidant supplements. But, while the results of epidemiological studies have been almost uniformly positive, the results of clinical trials have remained largely inconclusive.

Some clinical trials were terminated prematurely because harmful effects of antioxidant supplements were observed. Indeed, the overwhelming evidence currently calls into question the preventive effect of antioxidant pills. On the contrary, they may be harmful, leading to an increased risk of mortality in people consuming them.

There are several possible explanations for the negative effect of antioxidant supplements. First, the “free radicals” that anti-oxidants act against perform a dual biological function. Free radicals are produced continuously in all cells as part of their normal functioning. In moderate concentrations, they are essential mediators of reactions by which our bodies eliminate unwanted cells.

By eliminating free radicals from our body, we interfere with important defensive mechanisms for eliminating damaged cells, including cancerous cells. So antioxidant substances can also harm people. Whereas our diets typically contain safe levels, highly concentrated antioxidant supplements can be hazardous.

In fact, the amounts of antioxidants that lend protection are not known and probably differ among individuals. People exposed to increased oxidative stress may have elevated antioxidant requirements.

Moreover, antioxidant supplements in pills are synthetic and biochemically unbalanced compared to their naturally occurring counterparts. Nor are they subjected to the same rigorous toxicity studies as other pharmaceutical agents. Indeed, we still lack substantial information on how our bodies metabolize them and how they interact with one another. As a result, it is still unclear whether dosage, duration of use, or parallel intake of other agents determine differences in their effect.

It also is unclear whether oxidative stress is a primary cause or a secondary phenomenon of chronic diseases, as well as of the aging process. In most human disease, oxidative stress is merely a symptom. So the link between oxidative stress and disease should not be overemphasized.

There are still many gaps in our knowledge of the mechanisms of action of antioxidant supplements. Basic issues concerning the efficacy and safety of consuming relatively high doses of antioxidant supplements need to be resolved. Results of ongoing clinical trials and further studies are required to improve our knowledge.

In the meantime, we know that antioxidants can cause unwanted health consequences. So the optimal source for antioxidants is diet, not supplements. In short, we should stop taking pills and eat more fruits and vegetables.

Goran Bjelakovic is Professor of Internal Medicine, University of Nis, Serbia.

Copyright: Project Syndicate, 2007.
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