Age at natural menopause and its associated factors in Canada: cross-sectional analyses from the Canadian Longitudinal Study on Aging

Does night work affect age at which menopause occurs?

PURPOSE OF REVIEW

To delineate the current state of evidence on the impact of night shift work on age at natural menopause.

RECENT FINDINGS

The only direct evidence is from a single observational study, which indicates that women who work night shifts are at moderately higher risk for earlier menopause and that this risk is more pronounced among younger women. Underlying biological mechanisms have yet to be sufficiently substantiated. A long-held line of inquiry, most strongly propagated by the observed link between night shift work and female breast cancer, is the 'Light at Night' hypothesis, which suggests melatonin-mediated circadian disruption as a potential regulator of reproductive signaling in women. Supporting evidence is found from observations of changes in endogenous melatonin production among night working women or in response to light exposure, and corresponding changes in endogenous ovarian hormone levels and modulated menstrual patterns, among other indications of altered central ovulation-governing processes. Susceptibility to night shift work may be modified by chronotype.

SUMMARY

This review summarizes the literature related to night work and ovulatory regulation in humans, prioritizing population-based evidence to provide motivation for the study of circadian disruption and night shift work as a regulator of menopausal timing.

Age at natural menopause and physical functioning in postmenopausal women: the Canadian Longitudinal Study on Aging

OBJECTIVE

The aim of this study was to evaluate the association between categories of age at natural menopause (ANM) and gait speed (slowness) and grip strength (weakness), common measures of physical functioning in older women.

METHODS

We analyzed data from the Canadian Longitudinal Study on Aging, which included participants from seven cities across Canada collected in 2012. The sample was restricted to women who reported to have entered menopause (N = 9,920). Women who had a hysterectomy before menopause were excluded since the age at which this surgical procedure was performed was not available. ANM was categorized into five groups: less than 40 (premature), 40 to 44 (early), 45 to 49, 50 to 54, and more than 54. We conducted linear regressions to assess the association between ANM and gait speed (m/s) and grip strength (kg) adjusting for participant age, education, body mass index, smoking, use of hormone therapy, height, and province of residence.

RESULTS

Mean ANM was 49.8 (95% confidence interval [CI]: 49.7-50.0), with 3.8% of women having a premature menopause; the average gait speed was 0.98 m/s (standard deviation: 0.22), the average grip strength was 26.6 kg (standard deviation: 6.39). Compared to women with ANM of 50 to 54, women with premature menopause had 0.054 m/s (95% CI -0.083, -0.026) lower gait speed when adjusting for age and study site. In the fully adjusted model, the association was attenuated, 0.032 m/s (95% CI -0.060, -0.004). ANM was not associated with grip strength.

CONCLUSION

Our study suggests that premature menopause (<40 years) may be associated with lower gait speed (slowness) among Canadian women. No association was observed between ANM and grip strength. Future studies should include a life course approach to evaluate whether social and biological pathways modify the association between age at menopause and physical function in populations from different contexts.