We all know sleep is important. But for bodybuilders and teens alike, it’s something akin to a secret weapon for growth — literally. Deep, restful sleep triggers a surge of growth hormone, fueling muscle and bone development, fat burning, and can even help bodies grow tall. But why does missing out on sleep disrupt this process?

A new study from UC Berkeley maps out the brain circuits that control growth hormone release during sleep, helping the team understand the findings’ broad implications for metabolic, cognitive and neurological health.

After studying brain circuitry in mice, researchers determined that growth hormone doesn’t just help build bodies — it also helps regulate blood sugar and burn fat, and it even plays a role in keeping your brain alert and focused.

But the system runs on a dime. Two hormones – growth hormone releasing hormone, or GHRH, and somatostatin [so·​mato·​stat·​in] – influence growth hormone during an individual’s REM and non-REM phases of sleep. During deep non-REM sleep, only GHRH’s level rises, nudging growth hormone into action. In REM sleep, by contrast, both hormones surge, further amplifying the effect of growth hormone.

Notably, growth hormone feeds back into a brain region called the locus coeruleus (se-Roo-lee-iss), which governs attention, arousal and cognition. Too little sleep lowers growth hormone. But too much growth hormone can actually nudge your brain toward wakefulness.

The takeaway? Sleep and growth hormone are in a delicate yin-yang dance, driving not just physical growth and repair, but also metabolic and cognitive function. So next time you’re tempted to sacrifice sleep, remember: The payoff extends far beyond your pillow.