Moderating Effects of Moderate-Intensity Physical Activity in the Relationship Between Depressive Symptoms and Interleukin-6 in Primary Care Patients

OBJECTIVE: To determine whether the relationship between interleukin (IL)-6 and depressive symptoms is moderated by participation in moderate-intensity physical activity in a sample of primary care patients. Elevated inflammation has been associated with a number of poor health outcomes. Depressive symptoms may be related to higher levels of the inflammatory marker IL-6; however, previous findings are inconsistent, possibly due to unidentified moderating factors. METHODS: A total of 107 participants, aged ≥ 40 years, were recruited in Rochester, New York, in 2006 to 2007. Depressive symptoms were measured by the Center for Epidemiologic Studies Depression Scale-Revised, participation in moderate-intensity physical activity was measured using a modified version of the Community Health Activities Model Program for Seniors Activity Questionnaire for Older Adults, and serum IL-6 concentrations were determined using standard enzyme-linked immunosorbent assay protocols and high-sensitivity, anti-cytokine antibody pairs. A hierarchical multiple regression analysis was conducted. RESULTS: The correlation between IL-6 and depressive symptoms was nonsignificant (r = .086, p = .40). The association between IL-6 and depressive symptoms was moderated by participation in moderate-intensity physical activity (p = .02). Among those who did not engage in moderate-intensity physical activity, higher levels of depressive symptoms were significantly associated with higher levels of IL-6 (r = .28, p = .05), whereas this association was not significant among those who did participate in moderate-intensity physical activity (r = -.13, p = .38). CONCLUSION: Participation in moderate-intensity physical activity may buffer the risk of higher inflammation often associated with higher levels of depressive symptoms.