Through a pair of opposing signals from the hypothalamus. In a UC Berkeley study in mice, published in the journal Cell, researchers found that during non-REM (deep) sleep, neurons that make somatostatin, which suppresses growth hormone, quiet down while neurons that make growth hormone-releasing hormone (GHRH) become moderately more active. That shift tells the pituitary gland to release more growth hormone. During REM sleep, both signals rise together, which also increases release.
The loop runs both ways: as growth hormone builds up during sleep, it stimulates the locus coeruleus, a brainstem region that controls alertness, which helps push the brain toward waking. Growth hormone helps maintain muscle and bone and regulates fat and blood sugar, which is why poor sleep may raise the risk of obesity and diabetes. The work was done in mice, so it still needs to be confirmed in humans.
Source: “Scientists discover how deep sleep builds muscle, burns fat, and boosts the brain,” ScienceDaily, from materials provided by the University of California, Berkeley (October 17, 2026); study: Ding et al., “Neuroendocrine circuit for sleep-dependent growth hormone release,” Cell 188(18), DOI 10.1016/j.cell.2025.05.039.
Image: The hypothalamus-pituitary complex. OpenStax College, CC BY 3.0, via Wikimedia Commons.