Antioxidants are substances believed to protect the body from the harmful effects of so-called free radicals, which may play a role in the development of cancer and heart disease . Examples of antioxidants include vitamin C, vitamin E, and zinc.

In the early to mid 1990s, a number of studies suggested a relationship between the intake of antioxidants or foods containing them, and a lower risk of cancer and heart disease. Subsequent studies, among them the Physicans’ Health Study and the Women’s Health Study, found no protective relationship between antioxidants and cancer or heart disease.

Earlier this month, the Annals of Internal Medicine reported that large doses of vitamin E (which many people take to prevent heart disease) may actually increase the risk of death. The Annals study evaluated therapeutic doses of the antioxidant, which are taken for a specific health effect and are far higher than the amounts found in food.

In the November 22, 2004 Archives of Internal Medicine , researchers analyzed the health effects of nutritional doses of antioxidants, amounts that could be consumed from the right mix of foods. They found that men—but not women—who took a low-dose antioxidant supplement were significantly less likely to get cancer than those who didn’t. Those men also had a reduced risk of death. The antioxidants did not reduce the risk of heart disease in men or women.

About the Study

Between October 1994 and June 1995, the researchers recruited 7,713 women, aged 35–60 years and 5,128 men, aged 45–60 years. Half of the study participants were assigned to take a daily antioxidant capsule containing: 120 milligrams (mg) vitamin C, 30 mg vitamin E, 6 mg beta carotene, 100 micrograms (µg) selenium, and 20 mg zinc. The other half took a daily placebo pill. Neither the study participants nor the researchers knew who was taking which pills until the completion of the study. Anyone already taking any of the vitamins or minerals in the antioxidant supplement was excluded from the study.

Each month, for 7.5 years, the study participants filled out a questionnaire detailing their pill consumption and any changes to their health status. In addition, at the beginning of the study and after two, five, and seven years, the researchers took blood samples to measure levels of antioxidants that could be affected by the intake of the antioxidant supplement. The participants also had recurring vision visits, which included screening tests for heart disease and cancer.

The researchers counted the number of fatal and nonfatal heart attacks , cancers, and total deaths in the antioxidant and placebo groups.

The Findings

The researchers found that the men who took the antioxidant pill were significantly less likely to develop cancer than men who took the placebo. This protective effect did not extend to women, and the antioxidant pill did not protect men or women against heart disease. However, men who took the antioxidant pill had a lower overall risk of death from any cause than men who took the placebo.

A major limitation of this study is that the researchers did not obtain any dietary information from the study participants. Antioxidants are readily available in fruits and vegetables as well as nuts, meats, and grains. Because the researchers were testing nutritional doses, it is likely that the amounts of these vitamins and minerals consumed in foods could have influenced the study results. In addition, the researchers did not track whether study participants started taking an antioxidant supplement (in addition to the pill they were assigned for the study) during the course of the study.

How Does This Affect You?

This study found that low-dose antioxidants help protect men against cancer. Does that mean that you should start taking a daily antioxidant pill? Probably not. This, after all, is one study among many that have demonstrated conflicting results, and if you already eat a diet rich in antioxidant nutrients, the results of this study do not provide any additional support for adding still more. And, researchers being unable to convincingly explain why only men benefited from low-dose antioxidant supplementation adds even more confusion to the picture.

Furthermore, the fact that another recent study reported an increase in the risk of death with high doses of vitamin E should give everyone pause when considering whether or not to supplement with antioxidants at all. The distinction here is in the dose.

With the role of supplements still up in the air, it seems best to consume whole foods that contain antioxidants, rather than the antioxidants themselves.

Food sources rich in the antioxidants mentioned in this study include:

  • Vitamin C : strawberries, oranges, broccoli, kale
  • Vitamin E : hazelnuts, tomato puree, peanut butter, corn oil, avocado
  • Beta carotene : sweet potatoes, carrots, squash, spinach
  • Selenium : Brazil nuts, canned tuna, shrimp, wheat
  • Zinc : canned oysters, turkey, wheat germ, chickpeas