The Truth About Antioxidants: Produce vs. Pills

By Russell H. Greenfield, MD Clinical Assistant Professor of Medicine UNC Chapel Hill School of Medicine

Posted on | By Russell H. Greenfield, MD

I want to believe that antioxidant supplements are good for me, for my family and for you. I have long been a believer, and maybe you have been, too. After all, we are long past the point of questioning whether vegetables and fruits are good for us – we accept that they are on the basis of remarkably consistent research results accumulated over decades that show how eating a variety of brightly colored produce on a daily basis helps reduce the risk for chronic illness such as heart disease, diabetes and even cancer. Our confidence in this concept is unshakable, even today.

Part of the reason that vegetables and fruits are believed to be so good for us, maybe even the primary reason, is that they contain important antioxidants. Our bodies need an adequate supply of antioxidants to limit the buildup of compounds called reactive oxygen species (ROS) that are normally produced as a byproduct of cellular energy production. ROS also accumulate when we are exposed to toxins such as tobacco smoke and radiation. When an excess amount of ROS exists, there is said to be a state of oxidative stress, a condition linked to the development of numerous health problems. It only makes sense then that adding more antioxidants to our systems should help lessen the chance for oxidative stress to occur and, by extension, help prevent illness.

Eating 5-9 servings of vegetables and fruits each day as is generally recommended can be hard. On the surface it would seem so much easier, even more efficient, to take high doses of the antioxidants found in produce in supplement form.

Linear thinking is comforting. To top it off, a large number of research trials suggest wide-ranging benefits from antioxidant supplementation. But more often than not, the human body does not behave in linear fashion and unintended consequences from what we assume to be healthy actions can occur.

A disturbing string of research results in recent years have suggested that high-dose antioxidant supplementation may have a dark side in select circumstances. At first, it was all too easy to dismiss these studies as outliers in the face of the overwhelming evidence of the benefits of antioxidant intake from food. Then studies were published strongly suggesting that high-dose supplementation with beta carotene, a type of provitamin A normally found in much lower concentrations in yellow/orange vegetables and fruits, increased the risk of cancer in people who smoke. More recent studies point to a heightened risk of prostate cancer among otherwise healthy men taking high-dose vitamin E, and to a possible association between high-dose selenium supplementation and an increased risk of skin cancer. The operative words are “high-dose” – not the naturally low concentrations found in food but the supernormal amounts present in many supplements, even some multivitamins.

Article written by Russell H. Greenfield, MD
Clinical Assistant Professor of MedicineUNC Chapel Hill School of Medicine