Current smoking at menopause rather than duration determines the onset of natural menopause.
BACKGROUND
Smoking has frequently been associated with early menopause. However, studies of this association have been inconclusive with regard to duration and intensity of smoking. A major problem in analyzing the effect of smoking duration on menopausal age is that both exposure and outcome are age-dependent.


METHODS
We calculated age-specific rates for categories of smoking duration and subsequently computed the rate ratios for occurrence of menopause. We were thus able to model the effect of smoking duration on 2 time scales without assumptions of linearity. We used data from a Dutch population-based cohort comprising 5544 women age 49-70 years who had experienced natural menopause.


RESULTS
The rate ratio (RR) for occurrence of menopause was increased in women who smoked in the year of menopause (RR = 1.41; 95% confidence interval = 1.32-1.50). The rate ratio of former smokers was similar to women who never smoked (0.95; 0.89-1.02). Prolonged exposure of smoking did not materially affect the risk of menopause, although the daily number of cigarettes currently smoked could increase the risk.


CONCLUSIONS
Perimenopausal smoking is apparently more important than smoking history in explaining an earlier age of onset of menopause among women who smoke.
van Asselt
Kristel M
KM
Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands. Kasselt@umcutrecht.nl
Kok
Helen S
HS
van Der Schouw
Yvonne T
YT
Grobbee
Diederick E
DE
te Velde
Egbert R
ER
Pearson
Peter L
PL
Peeters
Petra H M
PH
D000368:Aged; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008593:Menopause; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012907:Smoking / Q000453:epidemiology*; D013997:Time Factors