Many components of the immune system exhibit adverse change after marathon-type exertion. These immune changes occur in several compartments of the immune system and body (e.g. the skin, upper respiratory tract mucosal tissue, lung, peritoneal cavity, blood and muscle). Of all immune cells, natural killer (NK) cells, neutrophils and macrophages (of the innate immune system) exhibit the greatest changes in response to marathon competition, both in terms of numbers and function. Many mechanisms appear to be involved, including exercise-induced changes in stress
hormone and
cytokine concentrations,
body temperature changes, increases in blood flow and
dehydration. During this 'open window' of immune dysfunction (which may last between 3 and 72 hours, depending on the immune measure), viruses and bacteria may gain a foothold, increasing the risk of subclinical and clinical
infection. Of the various nutritional and pharmacological countermeasures to marathon-induced immune perturbations that have been evaluated thus far, ingestion of
carbohydrate beverages during intense and prolonged exercise has emerged as the most effective. However,
carbohydrate ingestion during a marathon attenuates increases in plasma
cytokines and stress
hormones, but is largely ineffective against changes in other immune components including suppression of NK and T-cell function, and salivary
IgA output. Other countermeasures, such as
glutamine,
antioxidant supplements and
ibuprofen, have had disappointing results and thus the search for companion agents to
carbohydrate continues.