CANCER, IMMUNE FUNCTION, AND PHYSICAL-ACTIVITY

Despite the problems of interpreting epidemiological studies and the d ifficulty in developing appropriate animal models, there is growing ev idence that moderate habitual physical activity can protect against ce r tain types of neoplasm, particularly tumors of the colon and the fem ale reproductive tract. Exercise programs also appeal to have a benefi cial influence on clinical course, at least in the early stages of the disease. Recent demonstration of exercise-induced changes in the acti vity of macrophages, natural killer cells, lymphokine activated killer cells, neutrophils, and regulating cytokines suggest that immune-modu lation may contribute to the protective value of exercise. Depression of immune function, such as in HIV infection and in old age, is associ ated with an enhanced susceptibility to tumors; but the sites of tumor igenesis in HN infection are not those that gain protection from physi cal activity. Further reseal ch is thus needed before it can be assert ed that favorable exercise-induced changes in immune function have a m aterial influence on the risks posed by various types of cancer.