Contributions of body mass index and exercise habits on inflammatory markers: a cohort study of middle-aged adults living in the USA

Objectives: Determine whether body mass index (BMI) and physical activity (PA) above, at or below MET minute per week (MMW) levels recommended in the 2008 Physical Activity Guidelines interact or have additive effects on interleukin (IL)-6, C reactive protein (CRP), fibrinogen, interleukin6 (IL-6) soluble receptor (IL-6sr), soluble E-selectin and soluble intracellular adhesion molecule (sICAM)-1. Design: Archived cohort data (n=1254, age 54.5 +/- 11.7 year, BMI 29.8 +/- 6.6 kg/m(2)) from the National Survey of Midlife Development in the USA (MIDUS) Biomarkers Study were analysed for concentrations of inflammatory markers using general linear models. MMW was defined as no regular exercise, <500 MMW, 500-1000 MMW, >1000 MMW and BMI was defined as <25, 25-29.9, >= 30 kg/m(2). Analyses were adjusted for age, sex, smoking and relevant medication use. Setting: Respondents reported to three centres to complete questionnaires and provide blood samples. Participants: Participants were men and women currently enroled in the MIDUS Biomarker Project (n=1254, 93% non-Hispanic white, average age 54.5 years). Primary outcome measures: Concentration of serum IL-6, CRP, fibrinogen, IL-6sr, sE-selectin and sICAM. Results: Significant interactions were found between BMI and MMW for CRP and sICAM-1 (p<0.05). CRP in overweight individuals was similar to that in obese individuals when no PA was reported, but it was similar to normal weight when any level of regular PA was reported. sICAM-1 was differentially lower in obese individuals who reported >1000 MMW compared to obese individuals reporting less exercise. Conclusions: The association of exercise with CRP and sICAM-1 differed by BMI, suggesting that regular exercise may buffer weight-associated elevations in CRP in overweight individuals while higher levels of exercise may be necessary to reduce sICAM-1 or CRP in obese individuals.