Sleep may look like a period of inactivity, but inside the brain, a complex network of nerve cells and hormones continues working. During sleep, the body releases growth hormone, which supports muscle and bone maintenance and helps regulate how stored fat is used. Now, scientists have mapped a brain circuit that helps control this process—and discovered that the hormone also sends signals back to the brain to influence wakefulness. The research, led by scientists at the University of California, Berkeley, and published in Cell, reveals a two-way relationship between sleep and growth hormone. It offers a closer look at how the brain coordinates physical recovery, metabolism and alertness.
The researchers focused on the hypothalamus, a brain region that regulates several essential functions, including sleep, body temperature and hormone release. Within it, they investigated neurons involved in controlling growth hormone secretion. Two key chemical messengers help regulate this process. Growth hormone-releasing hormone (GHRH) stimulates the release of growth hormone, while somatostatin suppresses it. Their activity helps control the amount of growth hormone released by the pituitary gland. To investigate how these signals change during sleep, the team recorded brain activity in mice and used techniques to stimulate specific neurons and trace connections between them. They found that the activity of these neurons changes across different sleep stages. During REM sleep, activity involving both GHRH and somatostatin increases. During non-REM sleep, somatostatin activity decreases while GHRH activity rises moderately. These different patterns can both promote growth hormone release.
The discovery did not end with hormone release. Researchers also identified a connection between growth hormone and the locus coeruleus, a brainstem region involved in alertness, attention and wakefulness. As growth hormone accumulates during sleep, it stimulates neurons in this region, helping regulate the transition towards waking. This creates a feedback loop: sleep promotes growth hormone release, and growth hormone, in turn, influences the brain circuits involved in waking up. The system appears to require careful balance. Too little sleep can disrupt growth hormone release, while excessive activity in wakefulness-related circuits may produce unexpected effects, including increased sleepiness.
What does this mean for health? Growth hormone supports muscle and bone maintenance and influences how the body processes fat and glucose. The newly mapped circuit therefore offers clues about how disrupted sleep might affect physical recovery and metabolic health. Its connection to brain regions involved in attention also raises questions about possible effects on cognitive function. However, the experiments were conducted in mice. Further research is needed to establish how closely this circuit operates in humans and whether it can be safely targeted to treat sleep or metabolic disorders. The findings do not mean that sleeping longer automatically builds muscle or burns body fat, either. Instead, the study reveals that sleep is an active biological process, coordinated by neural circuits and hormones that communicate continuously. Understanding this hidden conversation could eventually help researchers explain why healthy sleep matters not just for feeling rested, but also for maintaining the body’s long-term balance.
Sources:
Ding, X., Hwang, F.-J., Silverman, D., Zhong, P., Li, B., Ma, C., Lu, L., Jiang, G., Zhang, Z., Huang, X., Tu, X., [remaining authors], & Dan, Y. (2025). Neuroendocrine circuit for sleep-dependent growth hormone release. Cell, 188(18), 4968–4979.e12. https://doi.org/10.1016/j.cell.2025.05.039
