Your body is under constant assault from invading bacteria and virus es, as well as from your own mutating cells. A healthy immune system well- armed with white blood cells, antibodies, and certain proteins and other substances-will keep those invaders and renegades in check by destroying, devouring, or inactivating them. But a number of forces can undermine those defenses, increasing your risk of infection and possibly cancer, and slowing your recovery from illness. Weakened defenses can also give viruses that have been lurking in your system, sometimes for decades, an opportunity to pounce. For example, the virus that causes chicken pox in children can become active and cause shingles, a painful nerve disease.
You can help keep your immune system strong by eat ing and exercising wisely, taking certain supplements if necessary, minimizing stress, and avoiding external assaults, such as overexposure to the sun, ingestion of some pollutants and overuse of certain medications. Those measures offer protection even in older adults; contradicting the long-held notion that immunity inevitably declines with advancing age. Here are the details on what you can do to energize and maintain your body's defenses against disease.
FEED YOUR WHITE BLOOD CELLS
Scientists have long known that malnutrition-a grossly inadequate intake of protein and calories can devastate the body's immune system. Now they've confirmed that insufficient intakes of certain vitamins and minerals even moderate shortages that don't cause obvious signs of deficiency-can also undermine the body's weapons against infection and other diseases.
Nutrient shortfalls are fairly common, especially in older people who are unable to buy, prepare, and eat a balanced diet. Surveys indicate that about one-third of older people consume significantly less than the recommended amount of one or more nutrients.
The most frequently scanted nutrients include zinc, selenium, iron, the B vitamins (including folic acid), vitamins C and D, and beta-carotene. People who lack any of those tend to have signs of weakened immunity, mainly fewer and less active natural killer cells, a group of white blood cells that are the body's vital first line of defense against disease.
Several studies have found that correcting nutritional shortages can restore normal immune function and reduce the risk of infection as well. For example, Canadian researchers found that a multivitamin/mineral supplement taken daily for one year strengthened the body's defenses and reduced the risk and duration of infection in people who had marginally low levels of various nutrients. In well-nourished individuals, however, observational studies suggest that immune function remains relatively strong, even in most older people. Moreover, at least two clinical trials have found that taking multivitamin/mineral supplements did not lower the risk of infection in well-fed individuals.
The evidence on whether mega-doses of individual nutrients-notably vitamin E and zinc-can enhance immunity has been contradictory, especially in people who eat adequately. Indeed, a recent large clinical trial on this question found that well-nourished people who took extra vitamin E were sick longer and with worse symp toms during the IS-month study than those who took a placebo. As for extra vitamin C, there's little evidence that it helps treat colds and virtually none that it helps prevent them.