The mediating effect of chronic pain on the relationship between obesity and physical function and disability in older adults.

OBJECTIVES To determine the extent to which bodily pain mediates the effect of obesity on disability and physical function. DESIGN Cross-sectional analysis. SETTING Population-based sample of residents in the greater Boston area. PARTICIPANTS Community-dwelling adults aged 70 and older (N=736). MEASUREMENTS Body mass index (BMI), obtained from measured height and weight, was categorized as normal weight (19.0-24.9 kg/m2), overweight (25.0-29.9 kg/m2), or obese (≥30.0 kg/m2). Main outcome measures were the Physical Component Summary of the Medical Outcomes Study 12-item Short-Form Survey (PCS), activity of daily living (ADL) disability, and Short Physical Performance Battery (SPPB) score. Chronic pain was assessed according to the number of weight-bearing joint sites that had pain (hips, knees, feet and pain all over). RESULTS Older obese adults had greater ADL disability and lower SPPB and PCS scores than their nonobese counterparts, although in sex-stratified adjusted analyses, obesity was adversely associated with outcomes only in women. Obesity was associated with greater number of pain sites; and more pain sites were associated with greater odds of disability. Mediation analysis suggests that pain is a significant mediator (22-44%) of the adverse effect of obesity on disability and physical function in women. CONCLUSION Bodily pain may be an important treatable mediator of the adverse effect of obesity on disability and physical function in women.