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United States Department of Agriculture

Agricultural Research Service

Vitamins and Minerals, Free Radicals and Aging
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Jack T. Saari

People seem to be fascinated by aging. What causes it? How do we retard the effects of it? What, in a practical sense, constitutes the 'Fountain of Youth'? It is clear that we can expect to live longer than our grandparents. From a life expectancy of about 48 years in 1900, Americans are now expected to live beyond 75 years in the 21st century. This may be attributed to better protection against our environment, better nutrition and advances in medicine. But, these are largely advances in prevention of premature death. Even in the absence of life-shortening malnourishment, disease or accident, our bodies still age and deteriorate. What causes this?

Scientific observation has shown that aging causes reduced ability to use calories from food, reduced function of hormones, depressed enzyme function and reduced ability to fight disease. But what causes these changes? The most prevalent explanation is called the oxidative theory or free radical theory of aging. What the free radical theory says is that one of the substances that is essential for life, oxygen, is also harmful and becomes more so as we age. How does this happen? Oxygen in its various metabolic reactions in the body can be converted to undesirable by-products, called oxygen-derived free radicals, that are highly reactive and relatively indiscriminate in their destruction of protein, fat and DNA molecules, all of the molecules upon which our bodies' functions depend.

Fortunately, the body uses a variety of protective mechanisms against this destruction. This protection includes a variety of enzymes that are designed to destroy free radicals as well as food components, such as vitamins C and E and beta-carotene (a precursor of vitamin A), that combine with and inactivate free radicals. But these defenses, in particular the antioxidant enzymes, weaken with time and research indicates that good nutritional practices may help to defend against this decline.

Aging may be influenced by both the amount and by the type of foods that we eat. It is clear that our survival depends on getting enough food, but in modern society this is not a problem. In fact we are probably eating too much. In laboratory animals the only known way to prolong life is by food restriction, that is, by restricting intake by 5 to 40 percent of what they would eat if given free access to food (greater than 40 percent restriction results in signs of starvation). Food restriction reduces free radical production, which is one of the pieces of evidence for the free radical theory of aging. Whether food restriction retards human aging is not yet known. Studies on monkeys are currently in progress, but because monkeys live to 40 years of age, results won't be in for about 20 years. This indicates how difficult it is to do research in this area.

Another possible way of minimizing free radical damage is to eat foods that contain nutrients that will boost antioxidant defenses. Vitamin C is present in a wide variety of fruits and vegetables and beta-carotene is found in carrots, cantaloupe, dark-green leafy vegetables and vegetable-based soups. Vitamin E is found in vegetable oils, wheat germ, nuts and green leafy vegetables. It is unlikely that natural foods will provide too much of these vitamins, but those considering supplements should be aware that large doses of vitamin C or vitamin E may not be healthy, because they may promote free radical damage. So it's important to get enough, but not too much.

Other examples of antioxidant nutrients are the trace minerals - copper, zinc and selenium. These act as antioxidants because they are necessary components of specific antioxidant enzymes. Good dietary sources of copper and selenium are organ meats such as liver, seafoods, nuts and seeds. Zinc is found in meat, liver, eggs and seafood. Though essential to life because of their role in antioxidant and other enzyme functions, the trace minerals, like the vitamins, should be consumed in proper amounts, because excessive amounts that are not associated with enzymes may promote free radical formation.

Because the antioxidant nutrients, like most nutrients, have windows of greatest effectiveness, it is important to follow the recommended guidelines for their intake. The recommended intake for vitamin C is 75 milligrams for per day for women and 90 milligrams for men; increase these values by 35 mg per day if you're a smoker. For vitamin E, 15 milligrams per day (as alpha-tocopherol) is recommended. No specific amount is recommended for beta-carotene other than eating fruits and vegetables; supplements are not advised. For copper, the guideline is 1.5 to 3 milligrams per day. For zinc the recommended amount is 15 milligrams per day for men and 12 milligrams per day for women. The suggested amount of selenium is 55 micrograms per day. Following these guidelines may help to slow down the aging process by preventing free radical damage and contributing to your 'Fountain of Youth'.

Last Modified: 10/23/2006
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