By Lisa Rapaport

(Reuters Health) – – Women who have babies and breastfeed may be less likely to go through menopause early than those who don’t have children or nurse their infants, a U.S. study suggests.

Researchers tracked 108,887 women, ages 25 to 42, who had not yet gone through menopause. Just over half had experienced at least one pregnancy lasting at least six months and more than half of these mothers exclusively breastfed their babies for at least one month.

During follow-up for up to 25 years, women who had one pregnancy were 13% less likely to experience menopause before age 45, and the risk declined with subsequent pregnancies, the study found. Breastfeeding appeared to explain at least some of the reduced risk; after accounting for that factor, a single pregnancy was still associated with an 8% lower risk of early menopause.

“While most women may not be thinking about menopause timing when deciding how many children they plan to have, we feel our breastfeeding findings add new insight into ways to prevent early menopause,” said lead study author Christine Langton of the University of Massachusetts Amherst. “And they align nicely with recommendations of both the American Academy of Pediatrics and World Health Organization that U.S. women exclusively feed their infants breast milk for at least six months and continue breastfeeding for up to one year.”

Women go through menopause when they stop menstruating, which typically happens between ages 45 and 55. As the ovaries curb production of the hormones estrogen and progesterone, women can experience symptoms ranging from vaginal dryness to mood swings, joint pain and insomnia.

About 10% of U.S. women go through menopause before age 45, the authors note, and this has been linked to an increased risk of heart disease, osteoporosis, diabetes, cognitive decline and sleep problems, previous research has found.

Both pregnancy and breastfeeding might delay menopause by temporarily halting monthly ovulation cycles to release eggs, Langton said by email. Women are born with a set number of eggs, and depletion of this egg supply contributes to the end of menstruation and the start of menopause.

For the current study, researchers examined data from an ongoing long-term study of U.S. nurses, which began collecting data in 1989.

Overall, 59,388 women, or about 54%, had at least one pregnancy lasting at least six months and more than half of these mothers exclusively breastfed their babies for at least one month.

A total of 2,571 women, or 2.5%, went through menopause before age 45.

Women who had one pregnancy and only exclusively breastfed for less than one month still had a lower risk of early menopause than women who didn’t get pregnant. The risk of early menopause also declined more with subsequent pregnancies and longer periods of exclusive breastfeeding, researchers report in JAMA Network Open.

With two pregnancies, women were 16% less likely to go through early menopause, after researchers accounted for the duration of exclusive breastfeeding, while the risk was 19% lower with four or more pregnancies.

Researchers also found that nursing for one to six months was associated with a 5% lower risk of early menopause compared with breastfeeding for less than one month. Exclusive breastfeeding for 7-12 months was linked to a 38% lower risk.

The study wasn’t designed to determine whether pregnancy or breastfeeding influence menopause timing, or if other factors explain the association.

One limitation of the study is that most women were white and worked in the same profession, meaning the results might not apply to women of other racial or ethnic groups or with other types of careers.

More research is still needed to understand why and how pregnancy and breastfeeding might impact menopause timing before women consider weighing this as part of any family planning decisions, said Dr. Nanette Santoro of the University of Colorado School of Medicine, in Aurora.

“It’s been long suspected that processes that suppress ovarian function help to preserve the numbers of eggs left in the ovary,” Santoro, who wasn’t involved in the study, said by email. These effects are usually small and so it takes a very large population as in this study to demonstrate them.”

SOURCE: JAMA Network Open, online January 22, 2020.