Parity and breastfeeding were found to be inversely associated with risk for early menopause, according to the results of a longitudinal study published in JAMA Network Open.
Early menopause affects approximately 10% of women in the Western world and has been associated with an increased risk for premature mortality, cognitive decline, and cardiovascular disease. Studies investigating the association of reproductive factors with the timing of menopause have shown a significant inverse relationship between parity and risk for early onset of menopause, but few have examined risk for early menopause as an outcome.
To evaluate this, longitudinal questionnaire data from 108,887 women in the Nurses’ Health Study II, beginning in 1989, were used to assess the association of reproductive events as well as various other cofactors with early-onset natural menopause. The average age of premenopausal women at baseline was 34.1±4.6 years. Individuals who had a prior cancer diagnosis (except for nonmelanoma skin cancer) and those who had undergone a hysterectomy or an oophorectomy were excluded.
At baseline, respondents provided information regarding their medical history and health-related behaviors, such as use of oral contraceptives, menstrual and pregnancy history, and smoking status. Women were required to report whether they had been pregnant in the past 2 years and their number of pregnancies lasting ≥6 months. These assessments were updated every 2 years until 2009 (85%-90% response rates for each questionnaire cycle). Information regarding cumulative exclusive breastfeeding, defined as a period when no other liquids or solids were provided to the infant, and cumulative total breastfeeding was also collected. Age at menopause was defined as the age at which menstrual periods stopped for ≥12 consecutive months followed by consistent reporting of cessation on ≥3 consecutive questionnaires.
Age-adjusted models showed that compared with nulliparity, higher parity was associated with lower risk for early menopause: ≥4 pregnancies had a hazard ratio (HR) of 0.69 (95% CI, 0.58-0.83), whereas 1 pregnancy had an HR of 0.87 (95% CI, 0.77-0.99; P <.001 for trend). Adjustment for covariates such as smoking, alcohol intake, and oral contraceptive use and duration of use had minimal effect on the association of parity with early menopause.
Age-adjusted models also showed that longer duration of breastfeeding was associated with lower risk for early menopause. Cumulative total breastfeeding of ≥25 months was linked to significantly lower risk for early menopause compared with women who breastfed for <1 month (HR, 0.73; 95% CI, 0.63-0.85; P <.001 for trend). Exclusive breastfeeding was also associated with lower risk for early menopause: in fully-adjusted models that accounted for differences in parity, lower risk was observed in women who breastfed exclusively for 7 to 12 months (HR, 0.72; 95% CI, 0.62-0.83) and 13 to 18 months (HR, 0.80; 95% CI, 0.66-0.97) compared with women who breastfed for <1 month (P =.001 for trend).
In analyses that were stratified by parity, risk for early menopause was lowest in each stratum for women who breastfed for approximately 7 to 12 months compared with <1 month (2 pregnancies: HR, 0.79 [95% CI, 0.66-0.96]; ≥3 pregnancies: HR, 0.68 [95% CI, 0.52-0.88]). This association was nonlinear in these models, as risk was not significantly lower among women with cumulative exclusive breastfeeding of >12 months.
This is the first prospective cohort study to examine the association of breastfeeding with the risk for early menopause independent of parity. In addition to the other outcomes, the researchers found that the results were consistent with their hypothesis that exclusive breastfeeding would be more strongly associated with lower risk for early menopause than total breastfeeding, possibly because exclusive breastfeeding is more likely to suppress ovulation and therefore slow depletion of the ovarian pool.
Limitations to this study include the use of self-reporting, though verification through repeated questionnaires and medical records was utilized. In addition, the population examined was relatively homogeneous (93.9% non-Hispanic white), although there is no clear evidence that there would be significant variation in the physiologic association of reproductive factors and early menopause between races or ethnicities. Additional studies are necessary to validate these associations.
Langton CR, Whitcomb BW, Purdue-Smithe AC, et al. Association of party and breastfeeding with risk of early natural menopause. JAMA Netw Open. 2020;3(1):e1919615.