What makes a person immune to various diseases?
Thanks to the lymphocytes, the immune system possesses a memory, or a sense of history. The lymphocytes manufacture antibodies (proteins circulating in the blood) that attack intruders. Once you have produced antibodies to a certain microbea specific flu virus, for examplethat particular virus cannot make you sick again, because you have cells that immediately recognize it and produce the antibodies that destroy it. The immunity may last for years, sometimes for life. This is "acquired immunity."
Science has also developed vaccines. It all began in the late eighteenth century, when the English physician Edward Jenner observed that people who caught a mild disease called cowpox never got smallpox, which is related to it. Using a boy who had not had either disease, Jenner tried inoculation: he scraped the child's skin and applied secretions from cowpox sores, and the boy got cowpox. When Jenner later inoculated him with smallpox matter, the boy did not develop smallpox. (Such human experimentation would land Dr. Jenner in court today.)
Creating immunity by injecting healthy people with dead or altered disease-causing microbes has prevented millions of deaths from measles, polio, diphtheria, flu, smallpox, tetanus, yellow fever and many other diseases. Vaccines truly are immune-system boosters.
Does loss of sleep depress immunity?
It can. But losing sleep for a few nights won't necessarily make you ill. Many things boost or depress immunity temporarily. The number of immune cells rises and falls naturally in healthy people.
What foods boost immunity?
An adequate diet helps maintain immunity and keeps you healthy. The immune system needs such nutrients as protein, fatty acids, vitamins and minerals. Severely malnourished people are particularly vulnerable to immune dysfunction, and they get sick more easily than other people and stay sick longer. What most people want to know, though, is whether one specific food or kind of food will boost immunity in otherwise healthy people on an adequate diet. The answer is generally no.
What supplements boost it?
So far, there's no reason to believe that supplements will boost immunity in healthy people, except in the malnourished and many of the elderly. Though severe malnutrition is rare in the U.S., some groups, particularly the elderly, may be deficient in such nutrients as vitamin C, certain B vitamins, and zinc. Studies suggest that raising nutrient intakes to adequate levels can enhance immunity, and there is some evidence that elderly people stay healthier if they take a multivitamin/mineral pill. In contrast, other research suggests that megadoses of certain nutrients can significantly suppress some immune responses.
Consider zinc, for instance, found in meat and grains, and often promoted as an ideal immune-system booster when taken as a supplement. While some studies show that zinc supplements can boost immunity and promote wound-healing in the elderly, high intakes can actually suppress the immune response.
A diet low in beta carotene can depress immunity, but it's not clear that beta carotene supplements can correct the situation, or what levels of supplementation would be helpful. Among the agents that have been shown to stimulate immunity in experiments are bacteria such as those in yogurt, but it's far from certain that consuming yogurt (with or without live cultures) will promote resistance to disease.