Effects of body weight and fat mass on back pain - direct mechanical or indirect through inflammatory and metabolic parameters?

Background: while reports indicate the association between obesity and back pain, its mechanism is still unclear. Thus, we aimed to investigate the effects of weight and its components on back pain in middle-aged women while considering direct mechanical and indirect effects via inflammatory and metabolic parameters.Methods: we used data from the Chingford 1000 Women Study, two follow-ups seven years apart. We assessed effects of weight, body mass index (BMI), total fat mass (TFM), total lean mass (TLM) and total bone mineral density (TBMD), measured by dual-energy X-ray absorptiometry, on back pain episode. We used inflammatory (C-reactive protein, interleukin-6, and tumour necrosis factor-alpha) and metabolic parameters (systolic and diastolic blood pressure, triglyceride, high-density lipoprotein cholesterol, and fasting blood glucose) as mediators of indirect effects. We investigated associations of interest cross-sectionally and longitudinally using binary logistic regression and parallel mediation model.Results: we included 826 Chingford middle-aged women (mean age=60.7, SD=5.9) from the first used follow-up in cross-sectional and mediation analyses and 645 women that attended the follow-up seven years later, in longitudinal analyses. We found that increased weight was directly associated with increased odds of having back pain episode (OR=1.02; 95% CI 1.01-1.03), similarly as BMI (OR=1.05; 95% CI 1.02-1.08) and TFM (OR=1.03; 95% CI 1.01-1.04) consistently across the cross-sectional and longitudinal models, but not TLM or TBMD. However, we did not find consistent indirect effects of weight or its components through measured inflammatory or metabolic parameters on back pain.Conclusions: our results show that in middle-aged women, weight, BMI and TFM are directly related to back pain, indicating prominence of mechanical loading effect.