What about vitamin C?
This vitamin is necessary to good health and no doubt to immune function. But numerous studies have shown that vitamin C supplements have minimal or no effect on the immune response, unless you are deficient in C.
Does exercise boost immunity?
Some research shows that sedentary people don't have as vigorous an immune system as those who exercise. Moderate exercise (for example, a moderate walking program undertaken by previously sedentary people) seems to improve immune function. But there is also evidence that overdoing exercise may depress the immune system: high-intensity or prolonged endurance exercise steps up the output of two so-called stress hormones, adrenaline and cortisol, both of which can depress various components of the immune system.
Olympians and other highly trained athletes often report that after intense competition and training they are more susceptible to colds. Yet such news should not deter athletes from competing or exercisers from exercising.
The health benefits of exercise are clear. Regular aerobic exercise is good for the heart. Weight-bearing exercise builds bone and muscle. The idea that your immune cells might not show a response to your exercise program should not deter you from exercising or from beginning an exercise program if you are sedentary.
Can emotions affect the immune system?
States of mind surely affect health, and extreme emotional stress may damage immunity and bring on illness. But research into the link between mind and immunity is in its early stages and has produced very little solid evidence so farand not much advice about how to protect the immune system from the ill effects of emotional stress. An experiment may show that extreme grief depresses human T cells, for instance, but we don't know if the rest of the system is harmed, or whether the fluctuation means much.
Still, reports of increased illness and even death among the recently bereaved are common. Cancer patients with a "fighting spirit" seem to live longer than those who are despondent, but this may or may not prove something about immune function. Good social support is thought to improve immunity in people under stress.
Immune cells and nerve cells do interact. For example, when fighting an infection, immune cells are able to stimulate the brain to transmit the impulses that produce fever. Receptors for many of the chemicals released during stress, such as epinephrine and norepinephrine, have been observed on the surface of lymphocytes found near nerve terminals in the lymph nodes and spleen. This suggests that what goes on in the brain can interact with the immune system to suppress or, conversely, enhance it.
What does smoking do to immunity?
Part of the reason smokers are at risk for lung cancer and respiratory diseases may be that smoking suppresses immune cells. When smokers quit, immune activity begins to improve within 30 days.
When and why does the immune system malfunction?
The immune system has so many built-in fail-safes that, in theory at least, we should rarely fall ill. But, in fact, we do. Harmful agents such as HIV can baffle our defenses. The system can simply be overwhelmed by the number and toxicity of viruses, bacteria, or other foreign cells and toxins.
Though the immune system defends us against cancer, it is subject to cancer. Leukemia is a cancer of the white blood cells; multiple myeloma affects certain lymphocytes that produce antibodies. Cancers of the lymph system include lymphoma and Hodgkin's disease. Some of these cancers can now be successfully treated.
Sometimes the gatekeepers of the system go crazy, mistaking a basically inoffensive intruder such as pollen, dust, or a bit of bee venom for an enemy and causing the body to go into the red alert known as an allergic reaction. In addition, the immune system can mistake the body's own cells and tissues for "nonself" and attack them, as in auto-immune diseases like rheumatoid arthritis and systemic lupus.
The immune system will also reject and kill potentially lifesaving organ and tissue transplants, unless some way can be found to circumvent the reaction. Though in theory a pregnant woman's immune system should attack the fetuswhich is nonselfit doesn't. This is because the fetus itself produces a substance that shields it from the maternal defense system.
So how can I nurture my immune system?
Perhaps the most direct action you can take is to consume a varied, balanced diet of vegetables, fruits, whole and fortified grains and dairy products, with small amounts of fish and meat -- if you wish. A basic daily multivitamin/mineral supplement is usually a good idea for older people. Beware of any supplement, however, that promises to boost immunity: protein supplements, enzyme supplements and the whole range of specific vitamins, minerals, antioxidants and nostrums that claim to boost immunity.
Regular, moderate exercise is associated with good health and longevity and will benefit your cardiovascular system, whether it boosts immunity or not. Getting adequate sleep is also helpful. And, of course, don't smoke.