Sun exposure and age at natural menopause

Background: In a previous cross-sectional study we reported that under-exposure to sun may be associated with an earlier age at natural menopause (ANM). To confirm and extend these preliminary findings we conducted a larger study with detailed lifestyle assessment.
Methods: Between 09.2006-02.2008, a convenience sample of 1106 women, born between 1946-1962, who had no history of major chronic disease and conditions that may obscure the determination of ANM were recruited for a cross-sectional study in Isparta. A detailed assessment of premenopausal exposures including health related factors and lifetime lifestyle factors was performed. Cox proportional hazard modeling is used to determine predictors of ANM.
Results: Out of 1106 women, 508 (45.9 %) are postmenopausal. Median ANM is 52. Out of 1106, n=536 women reported premenopausal sunbathing. N=143 women reported <6hours of premenopausal lifetime weekly summer outdoors exposure; n=164 women reported <3hours of premenopausal lifetime weekly winter sun exposure; n=417 women reported pemenopausal ever use of calcium; n=174 women reported premenopausal ever use of vitamin D. In a multivariate model including variables related to sun exposure and physical activity as predictors, the sun exposure related variables: ever sunbathing before menopause, premenopausal summer outdoors exposure of ≥6hours/week, winter sun exposure of ≥3hours/week, ever use of calcium and vitamin D are independently associated with a later ANM, while cumulative exposures are not. Month of birth is also an independent predictor of ANM (being born in November and December is associated with a later ANM).
Conclusions: Ever sunbathing before menopause, premenopausal summer outdoors and winter sun exposure above a treshold, ever use of calcium and ever use of vitamin D before menopause predict a later ANM whereas cumulative exposures do not. To our knowledge this is the first large study suggesting an association between sun exposure related factors and ANM. Supported by TUBITAK-106S079(SBAG-3357).