Workplace lactation support attenuates the association between early maternal return to work and preschool overweight/obesity in China.

BACKGROUND: Maternal return to paid work may disrupt infant feeding continuity, yet its relationship with childhood adiposity remains uncertain. This study examined associations between return-to-work timing, breastfeeding, workplace lactation support, and preschool overweight/obesity in China. METHODS: This single-center cross-sectional study enrolled 1,633 mother-child dyads in Jiangxi Province, China, between February 2023 and August 2024. Children aged 36-72 months underwent standardized anthropometric assessment, and mothers reported return-to-work timing, breastfeeding duration, formula introduction, complementary feeding, and workplace lactation support. Multivariable logistic regression estimated adjusted odds ratios (ORs), with exploratory stratified and sensitivity analyses assessing heterogeneity by residence, maternal education, and workplace support. RESULTS: Overall, 458 children (28.0%) were overweight or obese. Among mothers, 733 (44.9%) did not return to paid work during the first postpartum year; 23 (1.4%) returned before 6 weeks, 260 (15.9%) at 6-15 weeks, and 617 (37.8%) at ≥16 weeks. Relative to no return, return at 6-15 weeks was associated with higher adjusted odds (OR 1.85, 95% CI 1.36-2.50), whereas return at ≥16 weeks was not (OR 1.06, 0.82-1.35). The estimate for return before 6 weeks was uninformative (n = 23; OR 2.23, 0.95-5.22), and the trend test was non-significant (p = 0.30). Inverse associations were observed for exclusive breastfeeding ≥6 months (OR 0.41, 0.26-0.63) and any breastfeeding 6-11 months (OR 0.61, 0.42-0.88); all pre-specified feeding-work interaction terms were null. In exploratory stratified analyses, return before 16 weeks was associated with overweight/obesity among mothers with low workplace support (OR 3.84, 2.25-6.56) but not high support (OR 1.08, 0.72-1.61; p-for interaction<0.001). CONCLUSION: Return at 6-15 postpartum weeks was the only timing category robustly associated with preschool overweight/obesity; no monotonic dose-response was evident. Sustained breastfeeding was associated with lower odds. The heterogeneity by workplace lactation support is exploratory in a study not powered for interaction and requires confirmation.