The hormonal changes that a woman experiences during pregnancy can actually reduce her risk of developing breast cancer later in life, the National Cancer Institute reports. A research team from the Georgetown Lombardi Comprehensive Cancer Center has identified a hormone linked to obesity that may counteract this protective effect.

"We know that pregnant women who gain an excessive amount of weight have high blood levels of leptin — a hormone made by fat tissue — and that they have an increased risk of developing breast cancer after menopause," said the study’s lead author Leena Hilakivi-Clarke, Ph.D. "By studying these factors in animals, we hope to understand how they're linked."

Obese or overweight pregnant women are susceptible to various other health concerns including gestational diabetes, hypertension, preeclampsia, and postpartum weight retention. They are also less likely to breastfeed, and stand the risk of delivering prematurely or having a child that is obese, the American Congress of Obstetricians and Gynecologists reports.

Dr. Hilakivi-Clarke and her colleagues observed gene changes in pregnant rats that were exposed to leptin and gauged their risk of developing breast cancer. Similar to humans, rats initially increase their breast cancer risk after giving birth, but diminish the possibility overtime. Rats that were exposed to leptin did not reduce their risk later in life.

"This is concerning, as it suggests the exposure to the obesity-linked hormone negated the protective effect of birth on breast cancer risk," Dr. Hilakivi-Clarke explained.

According to the National Cancer Institute, a woman’s risk of developing breast cancer is linked to her exposure to ovarian hormones such as endogenous estrogen and progesterone. Both pregnancy and breastfeeding limit the amount of menstrual cycles that a woman has in her life, which in turn reduces her exposure to these hormones that are produced by the ovaries.

"It appears that treating rats with leptin during pregnancy prevented the protective changes in genes from happening," Dr. Hilakivi-Clarke added. "This work points to an important direction for research to prevent breast cancer in women since obesity is an epidemic."

Source: Assis S, Wang M, Jin L, Bouker K, Hilakivi-Clarke L. Exposure to Excess Estradiol or Leptin during Pregnancy Increases Mammary Cancer Risk and Prevents Parity-Induced Protective Genomic Changes in Rats. Cancer Prevention Research. 2013.