Background
The dose-response relationships on the degree of smoking and age at natural menopause have been less clear.
Aim
To examine the effect of intensity, duration, cumulative dose, and timing of cigarette smoking on age at menopause using pooled data from 17 observational studies.
Method
A total of 207,231 and 27,580 postmenopausal women were included in the cross-sectional and prospective analyses, respectively. Information on smoking status, cigarettes smoked per day (intensity), smoking duration, pack-years (cumulative dose), age started and years since quitting smoking was collected. Age at menopause was categorised as <40 (premature), 40-44 (early), 45-49, 50-51 and ≥52 years.
Results
In both current and former smokers, higher intensity, longer duration, higher cumulative dose, earlier age at start smoking, and shorter time since quitting smoking were significantly associated with higher risk of earlier menopause. Duration (Bayesian information criterion (BIC): 366427.8) and cumulative dose (BIC: 381329.5) of smoking were two strong predictors of menopause age. Among current smokers with duration of 15-20 years, the risk was markedly higher for premature (15.58, 11.29-19.86) and early menopause (6.55, 5.04-8.52). Also, current smokers with 11-15 pack-years had over 4-fold (4.35, 2.78-5.92) and 3-fold (3.01, 2.15-4.21) risk of premature and early menopause respectively. Smokers who had quit smoking for more than ten years had similar risk as never smokers (1.04, 0.98-1.10).
Conclusion
The probability of earlier menopause is positively associated with intensity, duration, cumulative dose, and earlier initiation of smoking. Smoking duration is a much stronger predictor of premature and early menopause than others.