The mind and body act on each other in remarkable ways. Recent research indicates that the immune system is in direct contact with and under at least partial control of the part of the brain physiologically reactive to emotions. Thus there may be a biological link between emotions and disease and even death. Mortality is three times higher in individuals with few close relationships, whereas people with strong support groups have additional protection against life stressors. Death rates are higher for cancer patients with pessimistic attitudes. Illness is more common among people who feel locked into strife-ridden marriages. Conversely, AIDS patients with healthy psyches seem better able to withstand disease.

Any stressful situation takes its toll on the human body. Stress can be a primary enemy of overall health and a major contributor to disease. Because stress affects the immune system, the body becomes more susceptible to a multitude of ailments, from colds to cancer. Respiratory conditions, such as asthma, may become worse. The cardiovascular system reacts by constricting the blood vessels while increasing blood volume. The net result is a rise in blood pressure throughout a stress-ridden day. Multiple increases in blood pressure can eventually contribute to chronic high blood pressure. More forceful contraction of the heart elevates levels of free fatty acids, enhancing the development of clogged arteries leading to and including the heart itself. In extreme cases, sudden death can occur, especially if an individual has been experiencing high levels of uncontrolled stress for an extended period.