Our immune system is constantly under attack. Only when things go awry do we notice this efficient protective mechanism. Frequent colds, even if minor, and the presence of cold sores or other chronic infections are signs that the immune functions may be weak.

The immune system is composed of lymphatic vessels and organs (lymph nodes, thymus gland, spleen and tonsils), white blood cells (neutrophils, basophils, lymphocyctes, monocytes, etc.), specialized cells residing in various tissues (macrophages, mast cells, etc.) and specialized chemical factors (interferon, interleukin II, etc.).

The thymus gland is the major immune system gland. In general, the health of the thymus determines the health of the immune system. The thymus produces T-cells, a type of white blood cell responsible for cell-mediated immunity. Tests that examine the ratio of the different types of T-cells are useful to identify allergies, chronic fatigue syndrome, AIDS, rheumatoid arthritis and lupus.

Cell-mediated immunity is also important in resistance to mold-like bacteria, yeast, fungi, parasites and viruses (such as Herpes simplex, Epstein-Barr and viruses that cause hepatitis). Low blood levels of the thymus gland hormones (thymosin, thymopoietin or serum thymic factor) are associated with increased susceptibility to infection.

Lymph, the fluid in the lymph vessels, is filtered by macrophages in the lymph nodes; lymph also contains B-cells which, in turn, produce antibodies. Macrophages also reside in the liver and spleen; they protect these organs against invasion by microorganisms.

The spleen is important in fighting off bacterial infections; it produces white blood cells and engulfs and destroys bacteria and cellular debris. It is also a blood reservoir when needed; for instance, in case of hemorrhage, it can release its stored blood and prevent shock.

Maintaining a healthy immune system requires an almost holistic approach that involves lifestyle, stress management, exercise, diet and nutritional supplementation. Emotions such as anger or depression have a negative effect on the immune system, but happiness or optimism have a beneficial effect. Norman Cousins' book, Anatomy of an Illness, published in 1979, was scoffed at by many physicians, but recent research has supported the author's ideas by showing significant enhancement of immune function by positive emotional states.

The ravages of stress can be reduced during periods of rest, relaxation, meditation and sleep. In fact, during the deepest levels of sleep, strong immune-enhancing compounds are released. Seven to eight hours of quality sleep can significantly strengthen the immune system.

A good diet is essential. Nutrient deficiency, excessive consumption of sugar and high cholesterol levels in the blood can depress immune function. Increased levels of cholesterol inhibit the ability of white blood cells to divide, to move to areas of infection and to destroy microorganisms. Interestingly, L-carnitine, a popular supplement, has been shown to overcome the negative effects of elevated cholesterol on immune function. However, the effects of sugar were observed in three key studies in the 1970s. The consumption of sugar (about four ounces) suppressed the activity of white blood cells: The effects began within 30 minutes, lasted over five hours and typically resulted in a 50 percent reduction of activity at the peak time. The more sugar consumed, the greater the impairment of immune function.

The problem of nutrient deficiency may involve only one nutrient, but clinical studies suggest that even a mild deficiency can profoundly impair the immune system. Vitamin deficiency is widespread in the United States, particularly among the elderly. Nutritional experts recommend that elderly patients take a multiple-vitamin-and-mineral supplement daily.

Recent studies have shown that Vitamin B6 deficiency can suppress both antibody-related and cell-mediated immunity. B6 deficiency can result from low dietary intake, excess protein intake or consumption of alcohol or yellow food dyes. Folic acid deficiency is the most common deficiency in the United States; it has been shown to result in shrinkage of the thymus gland and the lymph nodes, and significantly impaired white blood cell function.

Other vitamins are critical for immune system health. Vitamin A helps maintain the surfaces of the skin and the respiratory and gastrointestinal tracts, the major barriers to microorganisms. It also stimulates the activity of white blood cells and antibodies. Vitamin C stimulates white blood cell activity, increases interferon levels and increases the levels of thymic hormones.

The foregoing dietary recommendations, along with a positive mental attitude and quality sleep time, will help to keep your immune system functioning at optimum levels throughout the chilly winter months.