How mothers adapt to the metabolic demands of nursing

Nursing poses major metabolic demands on mothers, to which they respond by eating more and saving energy to sustain milk production. There are significant hormonal changes during lactation, but how they lead to metabolic adaptations in nursing mothers remained unclear.

In this study, which appears in Nature Metabolism, leading researchers at Baylor College of Medicine and Pennington Biomedical Research Center uncovered a mechanism that connects prolactin, estrogen, the brain and metabolic adaptations during lactation.

“We worked with animal models to investigate how hormones and the brain work together to adapt to the metabolic demands nursing mothers face to sustain milk production,” said co-corresponding author Dr. Chunmei Wang, assistant professor of pediatrics at the USDA/ARS Children’s Nutrition Research Center at Baylor.

“Normally, estrogen helps control appetite and increases the body’s ability to burn fat, while prolactin does the opposite. During lactation, estrogen levels drop, and prolactin levels rise, leading to increased hunger and reduced fat-burning to compensate for extra energy demands posed by milk production and consumption,” said co-corresponding author Dr. Yanlin He, associate professor at Pennington Biomedical Research Center.

“We found that brain cells called estrogen receptor α (ERα) neurons in a small area of the hypothalamus are significantly less active during lactation,” said co-first author Dr. Meng Yu, postdoctoral associate in the Wang lab.

“We showed that when ERα is deleted from these neurons, prolactin levels rise, and the animals increase their appetite and save energy by burning less fat. It was striking to see that just eliminating ERα in this tiny brain region was able to sustain such major metabolic consequences.”

“When ERα neurons were removed in non-lactating female mice, the animals showed high prolactin levels and lactation-like changes—eating more and burning less fat. Reactivating these neurons in lactating mice reduced these effects, showing their role in controlling metabolism,” He said.

“I am excited that we have discovered a novel mechanism for prolactin regulation,” Wang said. “We knew that prolactin is produced by pituitary cells, and estrogen can act on these cells to increase prolactin levels. Here we found a novel role of estrogen in regulating prolactin levels—it activates ERα neurons in the hypothalamus, which in turn inhibits prolactin levels during lactation. These findings have potential clinical applications.”

“The study sheds light on how the brain integrates hormonal signals to regulate energy balance, which could have broader implications for understanding hyperprolactinemia—high levels of prolactin in the blood—obesity, menopause and other conditions where prolactin or estrogen levels shift. This work opens exciting avenues for future research on neuroendocrine control of metabolism,” He said.