Associations of reproductive factors and circadian syndrome in middle-aged and elderly women: A nationwide cross-sectional study from China, the United Kingdom and the United States.

Circadian Syndrome (CircS) was recently recognized as a novel predictor of cardiovascular disease (CVD) risk, with reproductive factors playing an important role in CVD risk. Yet, studies linking reproductive factors to CircS remain sparse. Data on middle-aged and elderly women were extracted from three nationally representative surveys: the China Health and Retirement Longitudinal Study (CHARLS) and the English Longitudinal Study on Ageing (ELSA) provided the training set, and the National Health and Nutrition Examination Survey (NHANES) constituted the validation set. We employed logistic regression to evaluate the association between self-reported reproductive factors and CircS risk, with inverse probability of treatment weighting (IPTW) and subgroup analyses conducted to verify the stability. A total of 11,721 participants were analyzed. CircS prevalence differed significantly across countries, with 51.40 % in China and 20.19 % in the United Kingdom. Early menarche (age <12 years) correlated with increased CircS risk in CHARLS (OR 1.38 [95 % CI 0.99-1.92]; p = 0.061), ELSA (OR 1.64 [95 % CI 1.36-1.98]; p < 0.001), and NHANES (OR1.52 [95 % CI: 1.21-1.89]; p < 0.001). Premature menopause (age <40 years) was associated with a roughly 30 % higher CircS risk. A shorter reproductive lifespan was significantly linked to CircS, with this relationship emerging at a reproductive lifespan of ≥40 years in CHARLS (OR1.39 [95 % CI: 1.04-1.84]; p = 0.024). The aforementioned correlations retained significance following IPTW and subgroup analyses. Early menarche, premature menopause, and abbreviated reproductive lifespans may negatively affect CircS. Public health strategies should incorporate menstrual cycle-related reproductive health into primary CircS prevention.