Smoking, body mass index, socioeconomic status and the menopausal transition in a British national cohort

Background This study investigates whether cigarette smoking, body mass index (BMI) and socioeconomic status are independently associated with age at menopausal transition. Methods Menopausal status and risk factor information were collected prospectively from 1572 British women followed up since their birth in 1946, so far until 50 years. Cox's regression models were used to investigate the relationships of interest. Results Cigarette smokers started the perimenopause and reached the menopause earlier than ex-smokers and non-smokers. The relative risk for smokers compared with non-smokers was 1.31 (95% CI: 1.09-1.56) for perimenopause and 1.63 (95% CI: 1.17-2.27) for menopause. Body mass index was associated with the age at inception of the perimenopause only among smokers and ex-smokers, with underweight women having the earliest perimenopause. No association was observed between BMI and age at menopause. Smokers and underweight women were more likely than others to start hormone replacement therapy (HRT) before becoming postmenopausal. There was no effect of education or social class on age at inception of the perimenopause or age at menopause. Single women had an earlier perimenopause but the effect was confounded by parity. Conclusions Smoking was independently related to an earlier menopausal transition, although the effect on inception of the perimenopause was particularly observed among underweight women. There was no independent effect of socioeconomic status. The popularity of HRT use in this cohort may have had an impact on the findings.