Adiposity and reproductive characteristics across the lifespan: a multi-ethnic population-based study in Northwest China

Background: Reproductive characteristics significantly shape physiological adaptations, little is known about how they relate to adiposity in women of multi-ethnic regions undergoing a rapid increase in obesity burden. This study aims to address this gap by assessing how reproductive patterns correlate with adiposity and identifying potential moderating factors among Chinese adults. Methods: In 2018–2019, 107,679 participants from the Regional Ethnic Cohort Study in China were included in this cross-sectional analysis. Restricted cubic spline and generalized linear regression models were used to assess the association of reproductive characteristics such as age at menarche and menopause, number of children, menopause status, duration of post-menopause, and reproductive years, as well as reproductive pattern with adiposity using body mass index (BMI). Reproductive pattern was characterized using a Higher-Risk Reproductive Score (HRRS), which incorporates key landmarks such as early menarche (≤ 12 years), having ≥ 3 children, and later age at menopause (≥ 51 years). Results: Females’ mean BMI was 24.4 (standard deviation, SD 3.8) kg/m², with the median age at menarche and menopause of 15.0 (interquartile range, IQR 2.0) and 49.0 (IQR 5.0), median number of children and reproductive years of 2.0 (IQR 1.0) and 34.0 (IQR 6.0). Age at menarche was non-linearly associated with an average drop of 0.13 kg/m² in BMI, particularly in Uyghur ethnic and younger adults. Age at menopause and reproductive years was non-linearly related to higher BMI by 0.05 and 0.07 kg/m² per year delay. Adiposity exhibited an inverted U-shape with number of children. The duration of post-menopause correlated with a BMI reduction of 0.08 kg/m² on average. The HRRS was associated with an increase of 0.56 kg/m² in BMI. Conclusions: Among Chinese women, earlier age at menarche and later age at menopause were associated with increased adiposity. Adiposity showed an inverted U-shaped relationship with number of children, and a higher-risk reproductive pattern was linked to increased adiposity.