At the center of all this is growth hormone, which surges during sleep. But scientists have long puzzled over why poor sleep, especially the early deep stage known as non-REM sleep, leads to lower levels of this critical hormone.

Scientists Discover the Brain Circuit Behind It

Researchers at the University of California, Berkeley, have now uncovered the answer. In a study published in Cell, they mapped the brain circuits that control growth hormone release during sleep and identified a new feedback system that keeps those levels in balance.

This discovery offers a clearer understanding of how sleep and hormones work together. It may also open the door to new treatments for sleep disorders linked to metabolic diseases like diabetes, as well as neurological conditions such as Parkinson’s and Alzheimer’s.

“People know that growth hormone release is tightly related to sleep, but only through drawing blood and checking growth hormone levels during sleep,” said study first author Xinlu Ding, a postdoctoral fellow in UC Berkeley’s Department of Neuroscience and the Helen Wills Neuroscience Institute. “We’re actually directly recording neural activity in mice to see what’s going on. We are providing a basic circuit to work on in the future to develop different treatments.”

Lack of sleep does more than leave you tired. Because growth hormone helps control how the body processes sugar and fat, poor sleep can increase the risk of obesity, diabetes, and heart disease.

The Brain Regions Driving Growth Hormone

The system behind this process is buried deep in the hypothalamus, an ancient part of the brain shared by all mammals. Here, specialized neurons release signals that either trigger or suppress growth hormone.

Two key players are growth hormone releasing hormone (GHRH), which stimulates release, and somatostatin, which inhibits it. Together, they coordinate hormone activity across the sleep-wake cycle.

Once growth hormone enters the system, it activates the locus coeruleus, a brainstem region that controls alertness, attention, and cognitive function. Disruptions in this area are linked to a wide range of neurological and psychiatric disorders.

“Understanding the neural circuit for growth hormone release could eventually point toward new hormonal therapies to improve sleep quality or restore normal growth hormone balance,” said Daniel Silverman, a UC Berkeley postdoctoral fellow and study co-author. “There are some experimental gene therapies where you target a specific cell type. This circuit could be a novel handle to try to dial back the excitability of the locus coeruleus, which hasn’t been talked about before.”

How Sleep Stages Control Hormone Release

To study this system, researchers recorded brain activity in mice by inserting electrodes and stimulating neurons with light. Because mice sleep in short bursts throughout the day and night, they provided a detailed view of how growth hormone changes across sleep stages.

The team found that GHRH and somatostatin behave differently depending on whether the brain is in REM or non-REM sleep.

During REM sleep, both hormones increase, leading to a surge in growth hormone. During non-REM sleep, somatostatin drops while GHRH rises more modestly, still boosting hormone levels but in a different pattern.

A Surprising Feedback Loop in the Brain

The researchers also uncovered a feedback loop that links growth hormone to wakefulness. As sleep continues, growth hormone gradually builds up and stimulates the locus coeruleus, nudging the brain toward waking.

But there is a twist. When this brain region becomes too active, it can actually trigger sleepiness instead, creating a delicate balance between sleep and alertness.

“This suggests that sleep and growth hormone form a tightly balanced system: Too little sleep reduces growth hormone release, and too much growth hormone can in turn push the brain toward wakefulness,” Silverman said. “Sleep drives growth hormone release, and growth hormone feeds back to regulate wakefulness, and this balance is essential for growth, repair and metabolic health.”

Why It Matters for Brain and Body

This balance does more than affect physical growth. Because growth hormone works through brain systems that control alertness, it may also influence how clearly you think and how focused you feel.

“Growth hormone not only helps you build your muscle and bones and reduce your fat tissue, but may also have cognitive benefits, promoting your overall arousal level when you wake up,” Ding said.

Funding and Research Team

The research was supported by the Howard Hughes Medical Institute (HHMI) and the Pivotal Life Sciences Chancellor’s Chair fund. Yang Dan holds the Pivotal Life Sciences Chancellor’s Chair in Neuroscience. The study also included collaborators from UC Berkeley and Stanford University.