Low serum IL-6 is associated with high 6-minute walking performance in asymptomatic women aged 20 to 70 years

Cross-sectional associations between low physical performance and inflammatory biomarkers have been reported in healthy subjects and in persons with specific disease conditions. In asymptomatic subjects, whether the inverse association between physical fitness and inflammatory biomarkers is dependent or is independent of fat mass, a significant source of inflammatory cytokines, and is independent of age, muscle mass and strength, endocrine, metabolic, and lifestyle factors is not known. Two hundred and twenty asymptomatic women aged 20 to 72 years with a C-reactive protein <5 mg/L were assessed for their mean speed over the 6-minute walking test (6MWS) and their serum IL-6, as well as body height, body weight, body lean and fat mass (measured by DXA), waist-to-hip ratio, grip and knee extension strength, physical activities (quantified by the QUANTAP questionnaire), tobacco consumption, serum 25(OH) vitamin D, parathyroid hormone (PTH), estradiol (E2), free testosterone, dehydroepiandrosterone sulfate (DHEAS), insulin-like growth factor (IGF-I), sex hormone-binding globulin (SHBG), calcium, albumin, and creatinine. In the step-wise multiple linear regression model, a 6MWS in the highest quartile (over 1.4 m/s) was associated with lower values of serum IL-6 (p = 0.02) and with higher values of grip strength (p = 0.04) and creatinine (p = 0.04). In conclusion, present results demonstrate that the relationship between lower levels of serum IL-6 and higher values of physical fitness in asymptomatic women is independent of age, body composition, and lifestyle, endocrine and metabolic confounders. It remains to be determined whether the inverse relationship between IL-6 and fitness reflects the presence of preclinical inflammatory diseases that could potentially influence fitness in asymptomatic women. (C) 2011 Elsevier Inc. All rights reserved.