Background Several studies have investigated the association of tobacco use with infertility and age at natural menopause, yet few have explored secondhand smoke (SHS) exposure with these outcomes. This study offers a comprehensive, quantified secondary data analysis of these issues using the Women's Health Initiative Observational Study (WHI OS).

Purpose This study examines associations between lifetime tobacco exposure—active smoking and SHS—and infertility and natural menopause (before age 50).

Methods Information on smoking, lifetime fertility status, and age at natural menopause was collected and available from 93 676 postmenopausal women aged 50–79 enrolled in the WHI OS from 1993 to 1998 at 40 centres in the USA. Multivariate-adjusted regression models were used to estimate ORs and 95% CI according to levels of active smoking and SHS exposure, and trends were tested across categories.

Results Overall, 15.4% of the 88 732 women included in the analysis on infertility met criteria for the condition. 45% of the 79 690 women included in the analysis on natural menopause (before age 50) met criteria for the condition. Active-ever smokers had overall OR's of 1.14 (95% CI 1.03 to 1.26) for infertility, and 1.26 (95% CI 1.16 to 1.35) for earlier menopause than never-smoking women. Never-smoking women with the highest levels of lifetime SHS exposure had adjusted OR's of 1.18 (95% CI 1.02 to 1.35) for infertility, and 1.18 (95% CI 1.06 to 1.31) for earlier menopause. Active-ever smokers reached menopause 21.7 months earlier than the mean of 49.4 years for never-smokers not exposed to SHS, and women exposed to the highest level of SHS reached menopause 13.0 months earlier.

Conclusions Active smoking and SHS exposure are associated with increased risk of infertility and natural menopause occurring before the age of 50 years.