During the past several years, antioxidant has become the buzzword du jour, which is term used to describe agents that combat the process of oxidation. Originally applied to preventing the oxidation of metals, such as the rusting of iron, and later extended to averting rancidity in foods, the meaning of this word has recently been extended to the study of cellular physiology in living tissue.

Early research demonstrated that the process of oxidation within the body’s cells could lead to the formation of free radicals, or molecules capable of producing damage as the body breaks down food or is exposed to environmental irritants, like tobacco smoke and radiation. This led to the hypothesis that interruption of this process could reduce cell damage and, hopefully, promote better health. For instance, early studies suggested that the interruption of oxidation may slow or possibly prevent cancer and arteriosclerosis, the latter because the oxidation of low-density lipoprotein (LDL, or “bad” cholesterol) is important in developing fatty buildups in the arteries, which can lead to heart attacks and strokes. More recent clinical trials, however, have failed to confirm this hypothesis. They have also failed to show that these supplements prevent cancer or help treating it.

The antioxidant supplements vitamin C, vitamin E, selenium, and carotenoids, such as beta-carotene, lycopene, and lutein, are all antioxidants. While often touted for their health benefits, research reveals that these antioxidants may offer little health benefit, according to the NIH. Here’s what the science says about their efficacy.

“Rigorous scientific studies involving more than 100,000 people combined have tested whether antioxidant supplements can help prevent chronic diseases, such as cardiovascular diseases, cancer, and cataracts,” explained the NIH. “In most instances, antioxidants did not reduce the risks of developing these diseases.”

Although official US nutritional guidance promotes eating antioxidant-rich fruits and vegetables for their health benefits, and those who eat healthy amounts of these foods exhibit lower rates of several illnesses, it’s unclear what role antioxidants play in disease prevention. It could be that other components of fruits and vegetables, or covariates, such as other lifestyle choices, actually prevent illness.

So let’s take a closer look at a few studies that the NIH cites to support its conclusion that antioxidant supplements may not be all they are cracked up to be.

Woman’s antioxidant cardiovascular study

In this trial from 2004, researchers tested whether antioxidant vitamins and a folic acid/vitamin B6/vitamin B12 combination decreased risk for future cardiovascular events in 8,171 women with preexisting cardiovascular disease (CVD) or CVD risk factors.

“Although a definitive conclusion regarding generalizability requires additional trials in diverse populations, there is little biological basis for supposing that the benefit-risk balance differs in other high-risk women,” the authors concluded.

Physicians’ health study II

Multivitamins are the most frequently taken dietary supplement in the United States. In this randomized trial, 14,641 male physicians aged 50 years or more took either multivitamins or placebo, with follow-up from 1997 to 2011. Endpoints in this study included all cardiovascular diseases.

“Among this population of US male physicians, taking a daily multivitamin did not reduce major cardiovascular events and mortality after more than a decade of treatment and follow-up,” concluded the authors. Vitamin E and vitamin C supplements failed to decrease the risk of these diseases; moreover, vitamin E supplementation was tied to a higher risk of certain strokes, among other findings.

SELECT trial

Researchers in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) examined whether these supplements could prevent prostate cancer when compared with placebo. The trial was funded by the National Cancer Institute, with more than 35,000 men aged 50 years and older participating at hundreds of clinical sites.

Not only did these supplements fail to prevent prostate cancer, on longer follow-up, they actually predicted risk of prostate cancer. “The additional data show that the men who took vitamin E alone had a 17 percent relative increase in numbers of prostate cancers compared to men on placebo,” the authors wrote.

The NIH researchers did suggest certain reasons why the selenium supplements failed to decrease cancer risk, including excessive dosing and decreased bioactivity. Furthermore, they noted, “it may be that selenium only reduces the risk of prostate cancer in selenium-deficient men and not in the general population.”

Antioxidants and cancer

These supplements may decrease the favorable effects of chemotherapy. In a trial involving 1,134 participants, researchers publishing in the Journal of Clinical Oncology found that vitamins A, C, and E, carotenoids, and coenzyme Q10 taken before and during chemotherapy for breast cancer were related to an increased hazard of recurrence, as well as increased risk of death. “Associations between survival outcomes and use of antioxidant and other dietary supplements both before and during chemotherapy are consistent with recommendations for caution among patients when considering the use of supplements, other than a multivitamin, during chemotherapy,” the authors wrote.

In addition to this example cited above, high-dose beta-carotene supplementation may actually increase the risk of developing lung cancer.


In the aggregate, antioxidant supplements per se do little or nothing to facilitate better health. In fact, they may actually be unhealthy in certain situations.

These findings are unfortunate because antioxidants had shown promise in preclinical studies, where they readily stabilize free radicals. Ultimately, not all research translates from the laboratory to the “real world.” In the case of antioxidants—unless deficiency is an issue—it is far better to obtain them from a balanced diet.


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