Cigarette smoking and the risk of natural menopause.

We reviewed published studies on the association of age at natural menopause and cigarette smoking. All demonstrated an earlier median or mean age of menopause among smokers; for current smokers vs noncurrent smokers the difference ranged from 0.8 to 1.7 years. For studies that presented suitable data, we computed prevalence odds ratios of menopause for current smokers vs never-smokers, current smokers vs noncurrent smokers, and former smokers vs never-smokers. The Mantel-Haenzel summary odds ratios and 95% confidence intervals for these contrasts were: 1.9 (1.7-2.2), 1.7 (1.5-1.9), and 1.3 (1.0-1.7). Studies that presented data on amount of cigarettes smoked per day demonstrated "dose-response" trends when analyzed using the Mantel-Haenszel extension. The consistency of results across studies, the persistence of the effect when age and other covariates were considered, and the dose-response relation all support the hypothesis that smoking increases the risk of early menopause.