by Anne Eglash MD, IBCLC, FABM
Does breastfeeding protect women from endometrial cancer? Endometrial cancer occurs in the lining of the uterus, and the cancer grows in response to a relatively high estrogen level. Women who are obese have a higher risk of endometrial cancer because their body fat makes estrogen. Taking estrogen pills without progesterone also increases the risk of endometrial cancer.
Women who have had several pregnancies, who have used an IUD with progesterone, or who have taken the combined birth control pill have a lower risk of endometrial cancer.
A breastfeeding woman typically has a lower estrogen level because she is not ovulating as often in comparison to a non-breastfeeding mother. The question is whether this lower estrogen level is associated with a lower risk of endometrial cancer. Several studies have evaluated this question, and the results have been mixed.
A recent systematic review combined the participants in several studies, to study the differences in breastfeeding rates and other factors among 17,241 control women vs 8981 women with endometrial cancer. All of the women had given birth in the past.
What do you suspect they found in their study, regarding the relationship between breastfeeding and risk of endometrial cancer? (choose 1 or more):
- Breastfeeding reduces the risk of endometrial cancer except for obese mothers.
- The longer a mother breastfeeds, the lower the risk of endometrial cancer, up to 6-9 months of breastfeeding.
- Breastfeeding a child for 2 years is not much more protective of endometrial cancer than breastfeeding for 1 year.
- Any breastfeeding is associated with an 11% reduced risk of endometrial cancer compared to never breastfeeding.
See the Answer
The answers are B, C, and D
Breastfeeding and Endometrial Cancer Risk: An Analysis From the Epidemiology of Endometrial Cancer Consortium
Jordan, Susan J. MBBS, PhD; Na, Renhua PhD; Johnatty, Sharon E. PhD; Wise, Lauren A. PhD; Adami, Hans Olov MD, PhD; Brinton, Louise A. PhD, MPH; Chen, Chu PhD; Cook, Linda S. PhD; Dal Maso, Luigino PhD; De Vivo, Immaculata PhD, MPH; Freudenheim, Jo L. PhD, MS; Friedenreich, Christine M. PhD, MSc; La Vecchia, Carlo MD, MSc; McCann, Susan E. PhD, RD; Moysich, Kirsten B. PhD, MS; Lu, Lingeng PhD, MD; Olson, Sara H. PhD; Palmer, Julie R. ScD, MPH; Petruzella, Stacey MPH; Pike, Malcolm C. PhD; Rebbeck, Timothy R. PhD; Ricceri, Fulvio PhD; Risch, Harvey A. MD, PhD; Sacerdote, Carlotta PhD; Setiawan, Veronica Wendy PhD; Sponholtz, Todd R. PhD; Shu, Xiao Ou MD, PhD; Spurdle, Amanda B. PhD; Weiderpass, Elisabete MD, PhD; Wentzensen, Nicolas MD, PhD; Yang, Hannah P. ScM, PhD; Yu, Herbert MD, PhD; Webb, Penelope M. MA, DPhil
Obstetrics & Gynecology: June 2017 – Volume 129 – Issue 6 – p 1059–1067
OBJECTIVE:
To investigate the association between breastfeeding and endometrial cancer risk using pooled data from 17 studies participating in the Epidemiology of Endometrial Cancer Consortium.
METHODS:
We conducted a meta-analysis with individual-level data from three cohort and 14 case–control studies. Study-specific odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for the association between breastfeeding and risk of endometrial cancer using multivariable logistic regression and pooled using random-effects meta-analysis. We investigated between-study heterogeneity with I 2 and Q statistics and metaregression.
RESULTS:
After excluding nulliparous women, the analyses included 8,981 women with endometrial cancer and 17,241 women in a control group. Ever breastfeeding was associated with an 11% reduction in risk of endometrial cancer (pooled OR 0.89, 95% CI 0.81–0.98). Longer average duration of breastfeeding per child was associated with lower risk of endometrial cancer, although there appeared to be some leveling of this effect beyond 6–9 months. The association with ever breastfeeding was not explained by greater parity and did not vary notably by body mass index or histologic subtype (grouped as endometrioid and mucinous compared with serous and clear cell).
CONCLUSION:
Our findings suggest that reducing endometrial cancer risk can be added to the list of maternal benefits associated with breastfeeding. Ongoing promotion, support, and facilitation of this safe and beneficial behavior might therefore contribute to the prevention of this increasingly common cancer.
Milk Mob Comment by Anne Eglash MD, IBCLC, FABM
The goal of this systematic review was to determine whether breastfeeding itself is associated with a decreased risk of endometrial cancer for all women, or whether it was only protective for women who already had a reduced risk, such as women who are not obese, and who have taken the birth control pill.
This study demonstrates that breastfeeding reduces the risk of endometrial cancer for all breastfeeding women, even if they have a high BMI. Breastfeeding for 6-9 months is significantly more protective than breastfeeding for 0-3 months. However, breastfeeding past 9 months does not seem much more protective than breastfeeding for 6-9 months and there are a few possible reasons for this. First of all, these studies did not have large numbers of women nursing past a year, so it was harder to study this effect. In addition, women often have return of their menses by 9 months postpartum even if they are nursing. At that point, their estrogen levels have risen, so the lower estrogen effect from breastfeeding is gone.
Based on this work, I feel that we can more confidently say that women who do not breastfeed have a higher risk of endometrial cancer.