The relation of age at menarche with age at natural menopause : a population study of 336 788 women in Norway

STUDY QUESTION: Is age at menarche associated with age at menopause or with duration of the reproductive period (interval between menarche and menopause)? SUMMARY ANSWER: The association of age at menarche with age at menopause was weak and non-linear, and the duration of the reproductive period decreased by increasing age at menarche. WHAT IS KNOWN ALREADY: It remains uncertain whether age at menarche is associated with age at menopause. Some studies report that women with early menarche also have early menopause. Other studies report that women with early menarche have late menopause, or they report no association. The duration of the reproductive period may be an indicator of the cumulative endogenous exposure to estrogens and progestogens during life course and is associated with risk of breast cancer and endometrial cancer. STUDY DESIGN, SIZE, DURATION: A retrospective cohort study of 336 788 women, aged 48-71 years, in the BreastScreen Norway during the years 2006-2014 was performed. PARTICIPANTS/MATERIALS, SETTING, METHODS: Information about age at menarche and menopausal status was obtained by self-administered questionnaires. We used time to event approaches to estimate the associations. MAIN RESULTS AND THE ROLE OF CHANCE: Median age at menopause was 51 years in most menarche groups. Women with menarche at age 16 years or age >= 17 years had menopause 1 year later [median: 52 years, interquartile range (IQR): 49-54 years] than women with menarche at age 13 years (median: 51 years, IQR: 49-54 years, reference) (crude hazard ratio (HR) = 0.95; 95% CI: 0.93-0.97 and 0.95; 95% CI: 0.92-0.99, Pnon-linearity < 0.001). The reproductive period decreased with increasing age at menarche (Pnon-linearity < 0.001), and women with menarche at age <= 9 years had 9 years longer median reproductive period than women with menarche at age >= 17 years (median: 43 versus 34 years). Adjustment for year of birth did not change the HR estimates notably. LARGE SCALE DATA: Not applicable. LIMITATIONS, REASONS FOR CAUTION: Information about age at menarche and age at menopause was based on self-reports. Particularly for age at menarche, the long time interval between the event and data collection may have caused imprecise reporting. WIDER IMPLICATIONS OF THE FINDINGS: Our study suggests that age at menarche is a strong indicator for the duration of women's reproductive period. Our findings should encourage studies of the independent role of duration of the reproductive period on the risk of breast cancer and endometrial cancer, since these cancers have been associated with exposure to estrogens and progestogens. STUDY FUNDING/COMPETING INTEREST(S): The present study was funded by the Norwegian Cancer Society [Grant number 6863294-2015]. The authors declare no conflicts of interest