Differential impact of general and abdominal obesity on the labor–bone health association: a cross-sectional study in rural China

Rural populations in low-resource settings often experience high physical labor demands and limited health awareness, increasing their vulnerability to skeletal disorders. While obesity is known to influence bone health, general and central adiposity may exert divergent effects. The interplay between labor exposure, obesity phenotypes, and bone health remains underexplored, particularly in structurally disadvantaged populations. We analyzed data from 735 rural adults in Eastern China. Bone health was assessed using radial bone mineral density via dual-energy X-ray absorptiometry. Daily labor time was self-reported and categorized. Bayesian logistic regression estimated the association between labor time and bone health. Parallel mediation analysis assessed indirect effects through BMI and WHtR. Bayesian generalized additive models (GAMs) were used to examine nonlinear relationships, and subgroup analyses evaluated heterogeneity by gender alcohol use, and chronic disease status. Longer labor time was associated with better bone health (β = 0.42, 95% CI = [0.03, 0.81]). Mediation analysis revealed that BMI had a positive indirect effect (β = 0.27, 95%CI = [0.08, 0.50]), while WHtR exerted a negative effect (β = -0.09, 95%CI = [-0.21, -0.01]). GAMs identified nonlinear associations with diminishing benefits of increasing BMI and a U-shaped pattern for WHtR. Subgroup analysis indicated that the protective effect of BMI was more evident among women (β = 1.58, 95% CI = [1.07, 2.12]) and non-drinkers (β = 1.39, 95% CI = [0.99, 1.80]), while WHtR had stronger negative effects in females. Labor exposure affects bone health through distinct obesity-related pathways, with BMI and WHtR exhibiting opposing and population-specific effects. These findings underscore the need to consider adiposity type, labor conditions, and structural health disparities in designing targeted skeletal health interventions for rural communities.