Breastfeeding and Age at Menopause
by Anne Eglash MD, IBCLC, FABM
Menopause represents the time after which women no longer produce reproductive hormones necessary for childbearing, due to aging of the ovaries, with depletion of eggs. Women who are postmenopausal are at higher risk for bone loss (osteoporosis) and heart disease, so early menopause can have a negative effect on a woman’s long-term health. Menopause under the age of 45 is considered early.
Women who are pregnant don’t ovulate, and women who are breastfeeding ovulate much less. Some research has shown that breastfeeding and ovulation are associated with later aging of the ovaries due to less ovulation. The researchers wanted to further explore this in a large ongoing study, the Nurses' Health Study II.
The Nurses' Health Study II, with 116,429 women, began in June 1989 when baseline information on their health and life-style behaviors were measured. The participants continue to complete questionnaires every few years, tracking information such as pregnancies, breastfeeding duration, use of birth control pills, age of menopause, diet, habits, etc.
There are a number of variables that the researchers controlled for that play a role in age of menopause, including age at menarche, use of a birth control pill, race/ethnicity, BMI, smoking status, diet, and alcohol intake.
- Breastfeeding has to be exclusive for 6 months to prevent early menopause.
- Breastfeeding for 7-12 months is significantly associated with less risk of early menopause.
- Women who never have a child and never breastfeed have an increased risk for early menopause.
- Breastfeeding for longer than 12 months is more protective of early menopause as compared to breastfeeding for 7-12 months.
See the Answer
Pregnancy and breastfeeding prevent ovulation and may slow the depletion of the ovarian follicle pool. These factors may lower the risk of early menopause, a condition associated with increased risk of cardiovascular disease and other adverse health outcomes.
To examine the association of parity and breastfeeding with the risk of early menopause.
Design, Setting, and Participants
This population-based cohort study within the Nurses’ Health Study II cohort (1989-2015) included premenopausal participants who were aged 25 to 42 years at baseline. Response rates were 85%to 90% for each cycle, and follow-up continued until menopause, age 45 years, hysterectomy, oophorectomy, death, cancer diagnosis, loss to follow-up, or end of follow-up in May 2015. Hypotheses were formulated after data collection. Data analysis took place from February to July 2019.
Parity (ie, number of pregnancies lasting6 months) was measured at baseline and every 2 years. History and duration of total and exclusive breastfeeding were assessed 3 times during follow-up. Menopause status and age were assessed every 2 years.
Main Outcomes and Measures
Risk of natural menopause before age 45 years.
At baseline, 108 887 premenopausal women aged 25 to 42 years (mean [SD] age, 34.1 [4.6] years; 102 246 [93.9%] non-Hispanic white) were included in the study. In multivariable models, higher parity was associated with lower risk of early menopause. Hazard ratios were attenuated with adjustment for breastfeeding but remained significant. Compared with nulliparous women, those reporting 1, 2, 3, and 4 or more pregnancies lasting at least 6 months had hazard ratios for early menopause of 0.92 (95%CI, 0.79-1.06), 0.84 (95%CI, 0.73-0.96), 0.78 (95%CI, 0.67-0.92), and 0.81 (95%CI, 0.66-1.01), respectively (P for trend = .006). In multivariable models also adjusted for parity, hazard ratios for duration of exclusive breastfeeding of 1 to 6, 7 to 12, 13 to 18, and 19 or more months were 0.95 (95%CI, 0.85-1.07), 0.72 (95%CI, 0.62-0.83), 0.80 (95%CI, 0.66-0.97), and 0.89 (95%CI, 0.69-1.16), respectively, compared with less than 1 month of exclusive breastfeeding (P for trend = .001). Despite the significant test for trend, estimates were not observed to be lower as duration of exclusive breastfeeding increased. In a stratified analysis of parous women, risk of early menopause was lowest among those reporting exclusive breastfeeding for 7 to 12 months in each level of parity (women with 2 pregnancies and 7-12 months of breastfeeding: HR, 0.79; 95%CI, 0.66-0.96;3 pregnancies and 7-12 months of breastfeeding: HR, 0.68; 95%CI, 0.52-0.88; 2 pregnancies and13 months of breastfeeding: HR, 0.87; 95%CI, 0.66- 1.15; 3 pregnancies and 13-18 months of breastfeeding: HR, 0.86; 95%CI, 0.66-1.13; and 3 pregnancies and19 months of breastfeeding: HR, 0.98; 95%CI, 0.72-1.32).
Conclusions and Relevance
In this study, an inverse association of parity with risk of early menopause was observed. Breastfeeding was associated with significantly lower risk, even after accounting for parity. Breastfeeding at levels consistent with current recommendations may confer an additional benefit of lower risk of early menopause.
The researchers found that women who exclusively breastfeed for 7-12 months have the lowest risk of early menopause. However, women don’t need to nurse exclusively during the first year to have a reduced risk of early menopause. The risk of early menopause is decreased with increasing number of months of breastfeeding, up to 12 months.
The authors presume that exclusive breastfeeding is more protective than any breastfeeding because when women exclusively breastfeed, they are nursing more often and providing more milk volume than those partially breastfed, allowing for a higher prolactin level, which will help prevent ovulation.
The fact that exclusive breastfeeding for at least 7-12 months is most strongly associated with early menopause would be an additional reason for families to wait until 6 months to introduce complementary feedings.