MONDAY, Feb. 3, 2020 (HealthDay News) -- Both pregnancy and breastfeeding may protect women against early menopause, new research suggests.

The risk was lowest among those who breast-fed exclusively, meaning the baby received breast milk only -- no liquids or solid foods. Early menopause is the end of menstruation before age 45, the study authors said.

For the study, the researchers analyzed data from more than 108,000 U.S. women enrolled in the ongoing Nurses' Health Study II, which began in 1989.

"In our study, women with three or more pregnancies who breastfed exclusively for a total of seven to 12 months had about a 32% lower risk of early menopause compared to women with the same number of children who breastfed exclusively for less than one month," said study first author Christine Langton. She is a Ph.D. student at the University of Massachusetts Amherst's School of Public Health and Health Sciences.

Compared to women with no full-term pregnancies, women who had two pregnancies had a 16% lower risk of early menopause and women with three pregnancies had a 22% lower risk, the findings showed.

The study was published online recently in JAMA Network Open.

Pregnancy and breastfeeding generally prevent ovulation and may slow the natural depletion of ovarian follicles over time, thereby lowering the risk of early menopause, according to the researchers. But the study did not prove a cause-and-effect relationship.

Early menopause is associated with increased risk of heart disease, mental decline and osteoporosis.

"Our breastfeeding findings not only add new insight into ways to prevent early menopause, but 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," Langton said in a university news release.

"Our study has a lot of strength because of the large sample size, the 26 years of follow-up and the prospective design. Also, at baseline we limited our study to women who were premenopausal, which is a key point," she said.

More information

The U.S. Office on Women's Health has more about early menopause.