ObjectiveRegular physical activity may be associated with improved lung function via reduced systemic inflammation, although studies exploring this mechanism are rare. We evaluated the role of C-reactive protein in blood, which is a common marker of systemic inflammation, on the association of physical activity with forced expiratory volume in one second and forced vital capacity.MethodsCross-sectional data on spirometry, C-reactive protein levels and self-reported physical activity (yes/no; >= 2 times and.1hr per week of vigorous physical activity) were available in the European Community Respiratory Health Survey (N = 2347 adults, 49.3% male, 28-56 years-old). A subsample was also assessed 10 years later using the International Physical Activity Questionnaire, and tertiles of Metabolic Equivalent of Task-minutes per week spent in vigorous, moderate and walking activities were calculated (N = 671, 49.6% male, 40-67 years-old). Adjusted cross-sectional mixed linear regression models and the "mediate" package in "R" were used to assess the presence of mediation.ResultsDespite positive significant associations between nearly all physical activity metrics with forced expiratory volume in one second and forced vital capacity, there was no evidence that C-reactive protein levels played a role. An influence of C-reactive protein levels was only apparent in the smaller subsample when comparing the medium to low tertiles of moderate activity (mean difference [95% CIs]: 21.1ml [5.2, 41.9] for forced expiratory volume in one second and 17.3ml [2.6, 38.0] for forced vital capacity).ConclusionsIn a population of adults, we found no consistent evidence that the association of physical activity with forced expiratory volume in one second or forced vital capacity is influenced by the level of C-reactive protein in blood.