Overweight and obesity increase breast cancer risk in postmenopausal women: a meta-analysis of 38 observational studies.

Obesity is a recognized host-related factor associated with increased breast cancer (BC) risk-the most common malignancy and leading cause of cancer-related death among women. Menopausal status plays a critical role in this association due to hormonal and metabolic differences that may influence the impact of excess weight on carcinogenesis. This meta-analysis investigates the relationship between overweight, obesity, and BC risk, stratified by menopausal status. A systematic search of PubMed, Web of Science, and Cochrane Central Register of Controlled Trials databases (1987-2025) was conducted to identify observational studies examining the association between overweight, obesity, and BC risk. Odds ratios (ORs) and 95% confidence intervals (CIs) were extracted and pooled using a random-effects model. Subgroup analyses were performed for premenopausal and postmenopausal women. Publication bias was assessed through funnel plots and Egger's test. Thirty-eight independent studies were included, totaling 115,870 women. In postmenopausal women, both overweight (OR = 1.31; 95% CI 1.13-1.53) and obesity (OR = 1.43; 95% CI 1.25-1.63) were significantly associated with increased BC risk. Among premenopausal women, the associations were weaker and not statistically significant for either overweight (OR = 1.04; 95% CI 0.83-1.3) or obesity (OR = 1.11; 95% CI 0.89-1.38). Funnel plots showed no publication bias. Overweight and obesity significantly increase BC risk in postmenopausal women, but not in premenopausal women. These findings highlight the role of menopausal status and support the need for weight management strategies, particularly in postmenopausal women, to reduce obesity-related breast cancer risk.