Benefits of Antioxidants

By Paul E. Lemanski, MD, MS, FACP

Editor’s Note: This is the 117th in a series on optimal diet and lifestyle to help prevent and treat disease. Any planned change in diet, exercise or treatment should be discussed with and approved by your personal physician before implementation. The help of a registered dietitian in the implementation of dietary changes is strongly recommended.

Medicines are a mainstay of American life and the healthcare system not only because they are perceived to work by the individuals taking them, but also because their benefit may be shown by the objective assessment of scientific study. Clinical research trials have shown that some of the medicines of Western science may reduce the risk of Type 2 diabetes, heart attacks, strokes, cardiovascular death and even some cancers.

In the first 116 installments of the Non-Medicated Life, a healthy diet and lifestyle have been shown to accomplish naturally for the majority of individuals most of the benefits of medications in the prevention of the chronic medical conditions mentioned above. With respect to a healthy diet, much of the benefit for cardiovascular disease and cancer prevention has been attributed to the presence of the antioxidants in foods. This article will address the potential mechanisms of benefit, why antioxidant supplements do not appear to offer benefit, and those foods that contain the most potent antioxidants for preventing disease and maintaining health.

The energy necessary for life comes initially from sunlight. Through photosynthesis water, carbon dioxide, and minerals in the soil are converted into oxygen and energy containing organic compounds. When consumed by humans, these energy containing organic compounds are literally combined with oxygen (“burned” or oxidized) in cellular structures called mitochondria to produce energy for metabolism. While oxygen is necessary for the production of this energy, it may also contribute to the formation of so called “free radicals” that results in inflammation that may damage cellular structure and lead to disease. Thus, the primary role of antioxidants is to control the amount of inflammation and minimize damage to cellular structures.

For example, cholesterol deposited in the walls of arteries is, in part, a result of high LDL “the bad” cholesterol in the bloodstream. Nevertheless, LDL is inert in the artery wall until it becomes oxidized by reactive oxygen species produced in cells such as hydrogen peroxide, hypochlorous acid, the hydroxyl radical or the superoxide anion. Once oxidized, the LDL activates elements of the immune system to produce inflammation and disease. By minimizing oxidation and preventing and interfering with this resultant inflammatory response, the antioxidants present in fruits and vegetables have been shown to decrease heart attacks and strokes. 

In an observational study with follow up of five-million person-years, a higher pro-inflammatory diet pattern was associated with higher levels of inflammatory biomarkers such as high sensitivity CRP as well as higher rates of cardiovascular disease. Oxidized damage to DNA can also cause mutations in the DNA and potentially increase the likelihood for cancer. In the Lyon Diet Heart Study, a high omega-3 (plant based omega-3) Mediterranean diet containing substantial amounts of vegetables and fruits reduced fatal and non-fatal heart attacks by 70% and, additionally, decreased a number of different cancers when compared to a prudent Western diet.

However, the benefits of antioxidants present in fruits and vegetables does not appear to extend to antioxidants taken as isolated supplements. This may be because antioxidant supplements are given in non-physiological doses or because other cofactors in fruits and vegetables need to be present for the antioxidants to have maximal effect. In multiple clinical trials, antioxidant vitamins including vitamin E, vitamin C, and beta-carotene have shown no clear cardiovascular benefit. In the HDL Atherosclerosis Treatment Study (HATS) trial involving statin, niacin and an antioxidant cocktail including vitamin C, E, beta-carotene, and selenium the cardiovascular benefit of adding niacin to statin was offset when the antioxidants were added. One proposed explanation was that some oxidation was necessary to activate cellular repair mechanisms and complete suppression with high dose (non-physiological) antioxidants resulted in worse outcomes.

Other studies suggest antioxidant supplementation may increase cancer risk. The Beta-Carotene and Retinol Efficacy Trial (CARET) found that smokers supplemented with beta-carotene and vitamin A had increased rates of lung cancer. In the Alpha-Tocopherol, Beta-Carotene (ATBC) Cancer Prevention Study, the male smokers supplemented had a 17% higher incidence of lung cancer and an 8% higher all-cause mortality.

If the consumption of antioxidants in foods is beneficial, are some foods superior to others? Plants certainly top the list containing 64 times the antioxidant content compared to animal derived foods. Of the plants, berries are extremely high in antioxidants, especially those containing the darkly colored anthocyanin pigments present in blueberries and blackberries. Kiwifruit, strawberries, and raspberries are high. Green leafy vegetables are high in antioxidants, especially cruciferous vegetables such as kale, broccoli, broccoli sprouts, watercress, and Brussels sprouts, but also cauliflower, and cabbage, especially purple cabbage. Nuts and seeds, especially walnuts, almonds and flaxseed are also high. Green tea, and dried herbs and spices such as oregano, cinnamon, ginger, garlic, cumin and turmeric are all high in antioxidants and add both complexity of flavors and enhanced enjoyment to the health benefits.

In summary, antioxidants contained in foods provide much of the benefit of a healthy diet in reducing the risk of both cardiovascular disease and cancer. The mechanism of the benefit appears to be their ability to minimize the damage to cellular structures by reactive oxygen species produced by the burning of food for energy production. They reduce the oxidation of LDL cholesterol and the subsequent immune mediated inflammatory response which is the hallmark of atherosclerosis. They reduce the damage to DNA and resultant mutations that may promote cancer. Although such benefits occur with antioxidants contained in food, there is no evidence that when taken as a supplement a similar benefit results. By incorporating foods of known high antioxidant content into your diet, you may better assure health in the pursuit of the non-medicated life.

Paul E. Lemanski, MD, MS, FACP (plemanski3@gmail.com) is a board-certified internist practicing internal medicine and lifestyle medicine in Albany. Paul has a master’s degree in human nutrition, he’s an assistant clinical professor of medicine at Albany Medical College, and a fellow of the American College of Physicians.