by Anne Eglash MD, IBCLC, FABM
Does breastfeeding prevent endometriosis? Endometriosis is a chronic condition that affects approximately 10% of women in the United States. The endometrium is the lining of the uterus that becomes thickened during a woman’s menstrual cycle. If the woman is not pregnant at the end of the cycle, she sheds the thickened lining by menstruating. Women with endometriosis have little nests of endometrium that have migrated outside of the uterus, causing painful menstruation, and chronic abdominal/pelvic pain.
The Nurses Health Study II, which began enrolling participants in 1989, started collecting detailed information on their participants’ breastfeeding histories in 1997. Among approximately 72,000 enrolled participants who had ever been pregnant for more than 6 months, 3296 women had laparoscopically-confirmed endometriosis. The authors evaluated the relationship between duration of breastfeeding, exclusive breastfeeding, and rate of endometriosis. They controlled for many factors that can also influence the rate of endometriosis, such as body mass index, age, infertility history, number of pregnancies, age at menarche, smoking history, and history of oral contraceptive use.
What do you think the authors found regarding the relationship between endometriosis and breastfeeding? (choose 1 or more):
- Women who breastfed for at least 36 months in total had 40% less likelihood of having endometriosis compared to women who breastfed for less than 1 month.
- Every additional 3 months of breastfeeding during a pregnancy is associated with an 8% reduced risk of endometriosis.
- Postpartum amenorrhea (lack of menses) is not associated with the reduced risk of endometriosis among breastfeeding women.
- The relationship between breastfeeding and endometriosis lasts for at least 5 years after the last childbirth.
See the Answer
Answers: A, B, D (not C)
History of breast feeding and risk of incident endometriosis: prospective cohort study
BMJ 2017; 358 doi: https://doi.org/10.1136/bmj.j3778 (Published 29 August 2017)
Leslie V Farland, A Heather Eliassen, Rulla M Tamimi, Donna Spiegelman,Karin B Michels, Stacey A Missmer,
Objective: To investigate the association between lifetime breast feeding, exclusive breast feeding, postpartum amenorrhea, and incidence of endometriosis among parous women.
Design: Prospective cohort study.
Setting: Nurses’ Health Study II, 1989-2011.
Participants: 72,394 women who reported having one or more pregnancies that lasted at least six months, 3296 of whom had laparoscopically confirmed endometriosis. For each pregnancy, women reported duration of total breast feeding, exclusive breast feeding, and postpartum amenorrhea.
Main outcome measures: Incident self reported laparoscopically confirmed endometriosis (96% concordance with medical record) in parous women. Multivariable Cox proportional hazard models were used to calculate hazard ratios and 95% confidence intervals for diagnosis of endometriosis.
Results: Duration of total and exclusive breast feeding was significantly associated with decreased risk of endometriosis. Among women who reported a lifetime total length of breast feeding of less than one month, there were 453 endometriosis cases/100 000 person years compared with 184 cases/100 000 person years in women who reported a lifetime total of ≥36 months of breast feeding. For every additional three months of total breast feeding per pregnancy, women experienced an 8% lower risk of endometriosis (hazard ratio 0.92, 95% confidence interval 0.90 to 0.94; P<0.001 for trend) and a 14% lower risk for every additional three months of exclusive breast feeding per pregnancy (0.86, 0.81 to 0.90; P<0.001 for trend). Women who breastfed for ≥36 months in total across their reproductive lifetime had a 40% reduced risk of endometriosis compared with women who never breast fed (0.60, 0.50 to 0.72). The protective association with breast feeding was strongest among women who gave birth within the past five years (P=0.04 for interaction). The association with total breast feeding and exclusive breast feeding on endometriosis was partially influenced by postpartum amenorrhea (% mediated was 34% (95% confidence interval 15% to 59%) for total breast feeding and 57% (27% to 82%) for exclusive breast feeding).
Conclusion: Among women who experienced at least one pregnancy that lasted at least six months, breast feeding was inversely associated with risk of incident endometriosis. This association was partially, but not fully, influenced by postpartum amenorrhea, suggesting that breast feeding could influence the risk of endometriosis both through amenorrhea and other mechanisms. Given the chronic and incurable nature of endometriosis, breast feeding should be further investigated as an important modifiable behavior to mitigate risk for pregnant women.
Milk Mob Comment by Anne Eglash MD, IBCLC, FABM
The association between breastfeeding and reduced risk of endometriosis makes sense, because women who breastfeed exclusively or longer have later return of menses as compared to women who breastfeed less or who don’t breastfeed exclusively. According to ‘Sampson’s Theory’, endometriosis occurs from retrograde menses, meaning that some menses moves backwards from the uterus out thru the fallopian tubes, into the pelvis, as opposed to all menses emptying into the vagina. Based on this theory, lack of menses is thought to help prevent endometriosis.
However, these authors found that the amenorrhea experienced by breastfeeding women did not totally explain the reduced risk of endometriosis. There may be other physiologic factors in breastfeeding women that reduce the risk of endometriosis, such as the higher prolactin and oxytocin levels, or lower estrogen levels.
According to The Endometriosis Foundation of America women with a close family history of endometriosis have a 5-7 times increased risk of developing it. Based on this elaborate study, we can tell women at risk that there is good evidence that breastfeeding can reduce the risk of endometriosis, and this risk decreases the longer she breastfeeds.
SUE MADEJA
This is great information and evidence once again for the continued benefits of breastfeeding.
Thanks for these wonderful educational discussions!
Earlisha Killen
As someone who suffers from Endometriosis, I have noticed that my menstruation cycle hasn’t been as bad as it ever has been. I am also still currently bfing my LO (almost 15 months), and I have only have a few cycles and like I said, they have been a breeze!
Thank you for giving reputable resources for moms who struggle with endo and bfing a toddler.
My husbands grandmother made the comment this weekend about me nursing “too” long, thankfully my husbands cousin who is closer to her came to my defense, so this will help maybe convince her when the cousin isn’t around!