Linear regression between childhood passive smoking exposure and age at menarche (continuous) in women who had never smoked.

Model A: Unadjusted (n = 20,061). Model B: Adjusted for age (n = 20,061). Model C: Adjusted for age and education of the participants (n = 20,061). Model D: Adjusted for age and education, childhood family economic status, childhood family social status, frequency of eating meat and hunger as a child (phase 3 only; n = 6,697). The number of smokers and the frequency of exposure were included in the model separately. Linear regression between childhood passive smoking exposure and age at menarche (continuous) in women who had never smoked.