Aging, immune function, and exercise: hormonal regulation.

There is a known decline in immune function associated with aging which increases the risk for infectious diseases, tumorigenesis, and autoimmune disorders. As a result, older individuals demonstrating age-related immune dysfunction have significantly higher mortality rates. Alterations in neuroendocrine function play an important role in this immunosenescence as reductions in the ability to synthesize and release hormones and neurotransmitters, alterations in receptor number, density and affinity, diminished receptor responsiveness, and alterations in biochemical events distal to the hormone/receptor site are known to occur. It is becoming increasingly apparent that these age-associated neuroendocrine changes have a significant regulatory role in modulating immune function both at rest and in response to the stress of a single bout of exercise. In particular, this review will focus on age-related changes that are documented to occur in growth hormone, IGF-I, sympathetic nerve activity, catecholamine metabolism and responsiveness, and gonadal steroids. As a result of these neuroendocrine changes, older individuals are likely to respond differently to both acute and chronic exercise stimulation.