Antioxidants

Antioxidants are molecules that prevent or slow down the breakdown of other substances by oxygen.

In biology, antioxidants are scavengers of small, reactive molecules known as free radicals and include intracellular enzymes such as superoxide dismutase (SOD), catalase and glutathione peroxidase. Antioxidants can also be extracellular originating as exogenous cofactors such as vitamins. Nutrients functioning as antioxidants include vitamins, for example ascorbic acid (vitamin C), tocopherol (vitamin E) and vitamin A. Trace elements such as the divalent metal ions selenium and zinc also have antioxidant activity as does uric acid, an endogenous product of purine metabolism. Free radicals are molecules with one or more unpaired electrons, which can react rapidly with other molecules in processes of oxidation. They are the normal products of metabolism and are usually controlled by the antioxidants produced by the body or taken in as nutrients. However, stress, aging, and environmental sources such as polluted air and cigarette smoke can add to the number of free radicals in the body, creating an imbalance. The highly reactive free radicals can damage nucleic acids and have been linked to changes that accompany aging (such as age-related macular degeneration, an important cause of blindness in older people) and with disease processes that lead to cancer, heart disease, and stroke.

The brain is particularly vulnerable to oxidative stress. Free radicals play an important role in a number of neurological conditions including stroke, Parkinson disease, Alzheimer disease, epilepsy and schizophrenia. Some other diseases in which oxidative stress and depletion of antioxidant defence mechanisms are prominent features include hepatic cirrhosis, pre-eclampsia, pancreatitis, rheumatoid arthritis, mitochondrial diseases, systemic sclerosis, malaria, neonatal oxidative stress and renal dialysis.

Antioxidant simply refers to a molecule that protects cells from a process called oxidation, the negative effect of oxygen. Antioxidants act by neutralizing free radicals, which are atoms or groups of atoms that become destructive to cells when produced in large quantities. While our bodies naturally manufacture some antioxidant enzymes, it cannot manufacture selenium, the trace mineral necessary to produce these enzymes, nor can it manufacture the essential micronutrient antioxidants vitamins C, E, and beta-carotene and other carotinoids. They must be obtained by eating foods rich in these essential nutrients and, in some cases, supporting the diet with vitamin supplements.

To generate energy, cells must produce millions of chemical reactions. During this process, some oxygen molecules finish up with an odd instead of even number of electrons. Because each electron needs a mate, an unpaired electron makes the oxygen molecule unstable. These unstable molecules, called free radicals, then take an electron from a neighboring cell. The neighboring cell then becomes unstable, and affects its neighboring cell, starting a chain reaction. This domino effect becomes dangerous when the cell membrane or DNA is attacked, causing the cell to function poorly or die. When the body is unable to produce enough antioxidants to counteract free radicals, the resultant cell damage can cause certain types of cancer, heart disease, premature aging, cataracts, and other serious illnesses. For example, when free radicals damage artery walls, fatty deposits accumulate around the scar tissue, causing atherosclerosis and heart disease.

Most of the body's cells are continually exposed to free radicals, the creation of which is also stimulated by external sources such as tobacco smoke, smog, radiation, herbicides, and other environmental pollutants. Antioxidants are the body's mechanism for stabilizing free radicals. They work by donating one of their electrons to the unstable molecule, preventing the unpaired electron from "stealing" from another cell. Unlike oxygen molecules, antioxidants remain stable, even after donating an electron.