The mechanisms whereby regular exercise reduces chronic inflammation remain unclear. We investigated whether regular aerobic exercise alters basal levels of interleukin (IL)-10 and IL-4 in two randomized trials of physical activity. The Alberta Physical Activity and Breast Cancer Prevention Trial (ALPHA, n = 320) and the Breast Cancer and Exercise Trial in Alberta (BETA, n = 400) were two-center, two-armed randomized trials in inactive, healthy, postmenopausal women. Both trials included an exercise intervention prescribed five times/week and no dietary changes. In ALPHA, the exercise group was prescribed 225 min/week versus no activity in the controls. BETA examined dose-response effects comparing 300 (high) versus 150 (moderate) min/week. Plasma concentrations of IL-10 and IL-4 were measured at baseline, 6, and 12 months. Intention-to-treat (ITT) analysis was performed using linear mixed models adjusted for baseline biomarker concentrations. Circulating anti-inflammatory cytokine levels decreased among all groups, with percent change ranging from -3.4% (controls) to -8.2% (high) for IL-4 and -1.6% (controls) to -7.5% (high) for IL-10. No significant group differences were found for IL-4 (ALPHA p = 0.54; BETA p = 0.32) or IL-10 (ALPHA p = 0.84; BETA p = 0.68). Some evidence for moderation of the effect of exercise by baseline characteristics was found for IL-10 but not for IL-4. Results from these two large randomized aerobic exercise intervention trials suggest that aerobic exercise does not alter IL-10 or IL-4 in a manner consistent with chronic disease and cancer prevention.

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