Oxygen is a Jekyll and Hyde element. We need it for critical body functions, such as respiration and immune response, but the element’s dark side is a reactive chemical nature that can damage body cells and tissues. The perpetrators of this “oxidative damage” are various oxygen-containing molecules, most of which are types of free radicals—unstable, highly energized molecules that contain an unpaired electron.
Since stable chemical bonds require electron pairs, free radicals generated in the body steal electrons from nearby molecules, damaging vital cell components and body tissues. Oxidative damage in the body is akin to rusting of metal, the browning of freshly cut apples, or fats going rancid. Certain substances known as antioxidants, however, can help prevent this kind of damage. This article examines the special relationship between oxidative damage, antioxidant protection, diabetes, and complications of diabetes.
Free radicals and other “reactive oxygen species” are formed by a variety of normal processes within the body (including respiration and immune and inflammatory responses) as well as by elements outside the body, such as air pollutants, sunlight, and radiation. Whatever their source, reactive oxygen species can promote damage that is linked to increased risk of a variety of diseases and even to the aging process itself.
Oxidative damage to LDL (low-density lipoprotein or “bad”) cholesterol particles in the blood is believed to be a key factor in the progression of heart disease. Oxidative damage to fatty nerve tissue is linked to increased risk of various nervous system disorders, including Parkinson disease. Free radical damage to DNA can alter genetic material in the cell nucleus and, as a result, increase cancer risk. Cataract formation in the eye may also involve free radical damage to lens proteins. Oxidative damage has also been linked to arthritis and inflammatory conditions, shock and trauma, kidney disease, multiple sclerosis, bowel diseases, and diabetes.
As a defense against oxidative damage, the body normally maintains a variety of mechanisms to prevent such damage while allowing the use of oxygen for normal functions. Such “antioxidant protection” derives from sources both inside the body (endogenous) and outside the body (exogenous). Endogenous antioxidants include molecules and enzymes that neutralize free radicals and other reactive oxygen species, as well as metal-binding proteins that sequester iron and copper atoms (which can promote certain oxidative reactions if free). The body also makes several key antioxidant enzymes that help “recycle,” or regenerate, other antioxidants (such as vitamin C and vitamin E) that have been altered by their protective activity.
Exogenous antioxidants obtained from the diet also play an important role in the body’s antioxidant defense. These include vitamin C, vitamin E, carotenoids such as beta-carotene and lycopene, and other phytonutrients, or substances found in fruits, vegetables, and other plant foods that provide health benefits. Vitamin C (ascorbic acid), which is water-soluble, and vitamin E (tocopherol), which is fat-soluble, are especially effective antioxidants because they quench a variety of reactive oxygen species and are quickly regenerated back to their active form after they neutralize free radicals. Small amounts of these vitamins obtained from the diet provide a great deal of antioxidant protection, but research indicates that larger doses provide little additional protection. Vitamin C, which is abundant in fruits and vegetables, is concentrated in white blood cells that generate reactive oxygen species by using oxygen to burn bacterial and viral invaders; vitamin C may protect against DNA damage in the cell. Vitamin E, found in nuts, seeds, vegetable oils, and wheat germ, among other foods, protects unsaturated fat in cell membranes and fatty nerve tissue from oxidative degradation. Carotenoids, which are colored nutrients found in fruits and vegetables, provide their own unique antioxidant protection apart from vitamins C and E. Beta-carotene, the orange color in carrots, and lycopene, the red color in tomatoes, are effective quenchers of singlet oxygen, a form of reactive oxygen species that is not a free radical but is highly reactive.