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Overweight and obesity pose an increasingly large burden in the UK and worldwide. While unhealthy dietary habits and physical inactivity are the fundamental drivers of excess body weight, there is accruing evidence that reproductive health factors may also be determinants of overweight and obesity. Previous studies, however, generally focussed on a single reproductive factor (mostly age at menarche). In 500,000 individuals from the UK Biobank, we assessed the cross-sectional associations between reproductive health factors and a range of measures of body adiposity. The analyses confirm the previously reported inverse association between age at menarche and body adiposity. We also show that age at first birth was inversely associated with body adiposity in later life, whereas there was little evidence for an association between age at menopause and body adiposity. A novel finding is that the association between number of live birth and body adiposity in women is also present in men; men who had fathered four or more children had a higher BMI as compared to men without children. This suggests that a significant proportion of the association between parity and later adiposity can be attributed to behavioural risk factors associated with childrearing, and not to biological factors related to childbearing.