Antioxidants are part of the complex world of biochemistry. In cells, oxygen is constantly involved in chemical reactions in which electrons are shifted around. To generate energy, our cells remove electrons from sugars, fatty acids, and amino acids and add them to other molecules, especially oxygen. This process, called oxidation, creates highly reactive, unstable particles known as free radicals, which combine quickly with other compounds. There are many kinds of free radicals, which act in different ways. Normal cellular processes generate them, but so do other factors at the cellular level, including the effects of ultraviolet light, air pollution, trauma, excess heat, and smoking. When we exercise, we produce more free radicals because we inhale more oxygen and utilize more energy.
It takes a variety of antioxidants to help deactivate the different kinds of free radicals. The body’s natural antioxidant defense system is partly fueled by the antioxidants we consume. Some antioxidants are familiar—vitamin C, vitamin E, beta carotene and other carotenoids, and selenium. One big class of antioxidants in foods are polyphenols, which include flavonoids and are supplied by fruits, vegetables, and other plant-derived foods.
When free radicals overwhelm the antioxidant system, they cause oxidative damage, which has been implicated in many chronic diseases. They can cause LDL (“bad”) cholesterol to oxidize, increasing cardiovascular risk. They can also damage genes in ways that contribute to the aging process and may lead to cancer.
But free radicals sometimes come in handy. Our own cells actually produce them: Certain immune cells, including white blood cells, manufacture them and use them against invading organisms. They also help form some useful compounds in the body, including prostaglandins, which are hormone-like substances that have a variety of effects—for instance, on cell growth and pain regulation.