Breast-feeding is linked to a reduced risk for endometriosis, a new study reports.
Endometriosis — the growth of uterine tissue outside the uterus — can cause severe pain and excessive bleeding during menstruation, among other problems. It is a chronic disorder with an unknown cause.
Researchers studied 72,394 women who had had one or more pregnancies. There were 3,296 diagnoses of endometriosis among them. Compared with women who nursed for less than a month per pregnancy, those who nursed for a year or more had a 32 percent reduced risk for endometriosis. For each additional three months of nursing, they reduced their risk by 8 percent.
The study, in BMJ, controlled for body mass index, smoking, oral contraceptive use, age at menarche and other factors, but it depended on self-reports of breast-feeding, which are not always reliable.
The mechanism remains unclear, but women who stopped having periods for a time after giving birth also reduced their risk, and breast-feeding prolongs the pause in menstruation. Still, menstrual delay accounted for only a portion of the effect.
“Understanding risk factors for endometriosis that are modifiable is really important,” said the lead author, Leslie V. Farland, a research scientist at Brigham and Women’s Hospital in Boston. “And our finding builds on what we already know about breast-feeding — that it’s very beneficial for both the child and the mother.”