Physical activity and C-reactive protein levels: the confounding role of body fat

This study investigated the relationship between objectively-measured total physical activity (PA), and intensity of PA and high-sensitivity C-reactive protein (CRP) in 211 healthy, middle-age women (43.1±3.0 y). In addition, this study examined the extent to which age, BMI, abdominal circumference, and body fat percentage operated as confounders in these associations.

PA was objectively measured for 7 continuous days using accelerometry. Fasting blood samples were taken, from which CRP was measured using a solid phase ELISA. Body mass index (BMI) (kg/m2), abdominal circumference measured at the umbilicus, and body fat percentage using air displacement plethysmography, were assessed.

Total PA (activity counts) was significantly and inversely related to CRP concentrations (F=7.76, P=.006) as was vigorous-intensity PA. After adjusting for differences in body fat percentage, total PA and vigorous-intensity PA were no longer significant predictors of CRP. Abdominal circumference and BMI also tended to weaken the relationship between total or vigorous-intensity PA and CRP but not to the same extent as body fat percentage.

These findings suggest that higher total and vigorous-intensity PA levels are significantly related to lower CRP levels in healthy, middle-age women; however, this relationship is largely a function of differences in body fat percentage.