What is Growth hormone?

What is Growth hormone?

Growth hormone is one of the body's master metabolic hormones, released in pulses by the somatotroph cells of the anterior pituitary gland at the base of the brain. In children and adolescents it drives linear bone growth and is the reason you grow taller. In adults, whose growth plates have closed, its job shifts to maintenance: it helps control body composition, mobilizes stored fat for fuel, supports the repair of muscle, tendon, and bone, and keeps the metabolism of protein, fat, and sugar in balance.

Growth hormone rarely acts alone. Much of what people attribute to it is actually carried out by insulin-like growth factor 1 (IGF-1), a second hormone the liver produces in response to GH. The two form the GH/IGF-1 axis, the signalling system that ties together sleep, training, and nutrition. Blood levels are not steady through the day.

GH is released in roughly 8 to 12 bursts over 24 hours, and between bursts levels can fall close to zero, which is why a single blood test tells you very little. The single largest and most reliable burst comes in the first few hours of deep sleep. Output is highest during puberty, declines steadily through adult life, and is heavily shaped by how well you sleep, how hard you train, how much body fat you carry, and how you eat.

How it works

Growth hormone works through a tightly controlled feedback loop and two routes of action, direct and indirect. Release is governed by two signals from the hypothalamus: growth hormone-releasing hormone (GHRH), which switches secretion on, and somatostatin, which switches it off. The stomach hormone ghrelin also stimulates release, which is one reason an empty stomach and fasting raise GH.

Once in the blood, GH acts directly on fat cells to trigger lipolysis, the breakdown of stored triglycerides into free fatty acids that muscle and other tissues burn for fuel. This fat-sparing, glucose-sparing effect is central to how the body shifts toward burning fat during sleep, fasting, and prolonged exercise. At the same time GH is diabetogenic: it blunts insulin's action and nudges blood glucose up, preserving sugar for the brain.

The indirect route runs through the liver, which responds to GH by secreting IGF-1. IGF-1 is the main mediator of GH's growth and tissue-building effects, promoting cell division and collagen synthesis in muscle, tendon, cartilage, and bone. Together the axis favours repair and remodelling of connective tissue and supports recovery after training. Secretion is pulsatile and self-limiting: high GH and high IGF-1 both feed back to the hypothalamus and pituitary to raise somatostatin and shut further release down, which keeps the system from running away and is why levels rise and fall in sharp spikes rather than staying elevated.

How to apply it

• Protect deep sleep first: Deep, slow-wave sleep triggers the largest GH pulse of the day, and roughly 70% of a man's daily output can occur in early sleep. Consistent 7 to 9 hour nights and a regular schedule do more for GH than any supplement.
• Train hard with short rest: High-intensity resistance and interval work sharply raise GH for 15 to 30 minutes afterward. Moderate loads, higher reps, and short rest of 30 to 60 seconds produce the biggest acute spike, driven partly by rising blood lactate.
• Use the empty-stomach window: Fasting and low blood sugar raise GH through ghrelin and reduced insulin, which is why levels climb overnight and during longer fasts. A very large meal, especially high sugar, close to bedtime can blunt the early-sleep pulse.
• Keep body fat in a healthy range: Excess body fat, particularly visceral fat, suppresses GH secretion, while leaner individuals secrete more. Losing fat tends to restore a more youthful GH profile, so fat loss and GH support each other in a positive loop.
• Manage chronic stress: Persistently high cortisol from poor sleep, overtraining, or life stress works against GH-driven repair and favours a catabolic state. Deloads, rest days, and stress control let the recovery side of the axis do its work.
• Be skeptical of GH boosters: Over-the-counter HGH pills, sprays, and most amino-acid boosters have little evidence of raising GH meaningfully or changing body composition. The reliable levers are sleep, training, and body fat, not a supplement label promising a hormone surge.

Types

Worked example

Growth hormone is not released evenly across the day; it comes in pulses that different behaviours amplify or blunt. This table shows the main daily drivers and roughly how each one moves your GH, using figures reported in endocrinology and exercise research. The numbers are directional, not precise prescriptions, because pulse size varies with age, sex, and body fat.

Notice that the two biggest positive levers, deep sleep and hard training, are things you already control. That is the practical takeaway: you influence your own GH far more through sleep and training habits than through any pill or injection marketed as a shortcut.

Growth hormone vs IGF-1

GH and IGF-1 are two halves of one axis. GH gives the pulsatile command and handles fat and glucose directly; IGF-1 is the steadier downstream messenger that carries out most of the growth and repair. Because GH spikes and crashes, clinicians often measure IGF-1 to judge overall GH activity.

By goal

• Fat loss: GH genuinely supports fat metabolism, but you do not need to chase spikes. Prioritize enough sleep and a real calorie deficit; losing body fat itself restores healthier GH output. Treat any product promising a fat-burning GH surge as marketing, not physiology.
• Muscle and recovery: GH and IGF-1 aid connective-tissue repair and recovery, but acute post-workout spikes do not measurably add muscle in healthy trainees. Build muscle with progressive overload, adequate protein, and sleep; let GH support the repair rather than expecting it to drive growth.
• Older adults and general health: GH declines with age, but this is largely normal, and replacing it in healthy older people carries real risks such as insulin resistance and joint swelling. Resistance training, sleep, and staying lean support the axis far more safely than hormone products.

Common misconceptions

• "The GH spike from training is what builds your muscle." Controlled studies by West, Phillips and colleagues show the transient rise in GH, testosterone and IGF-1 after a workout does not enhance muscle protein synthesis, hypertrophy or strength beyond the training stimulus itself. Chasing a hormonal spike is not how you gain muscle.
• "Growth hormone is a shortcut to burning fat." GH does stimulate lipolysis, but that does not make it a fat-loss shortcut. Fat loss still requires an energy deficit, and injectable GH used for this brings side effects like insulin resistance, fluid retention and joint pain. Sleep and diet are the real levers.
• "Over-the-counter HGH pills and sprays raise your growth hormone." Most oral HGH boosters, sprays and amino-acid blends have little evidence of meaningfully raising GH or changing body composition. GH is a large peptide destroyed by digestion, so a pill cannot deliver it. The proven levers are sleep, training intensity and body fat.
• "More growth hormone is always better." Chronically high GH is harmful, not beneficial. The disease acromegaly, caused by GH excess, drives insulin resistance, enlarged organs, joint problems and higher mortality. The body pulses GH and shuts it off through somatostatin feedback precisely because sustained high levels cause damage.
• "GH falls with age, so training can't help older adults." GH does decline with age, but resistance training still builds muscle and strength at every age through mechanisms that do not depend on youthful GH levels. Older lifters gain muscle without restoring young-adult hormone profiles, so the decline is not a reason to stop training.

Related terms

Growth hormone FAQ

What does growth hormone do in the body?

Growth hormone regulates growth, body composition and metabolism. It stimulates the breakdown of stored fat for fuel, opposes insulin to spare blood sugar, and signals the liver to release IGF-1, which repairs and grows muscle, tendon, cartilage and bone. In children it also drives increases in height.

Does exercise increase growth hormone?

Yes. Hard resistance training and high-intensity intervals raise growth hormone sharply for about 15 to 30 minutes afterward. Moderate loads, higher reps and short rest periods of 30 to 60 seconds produce the biggest spike, partly because rising blood lactate stimulates release. The effect is real but short-lived.

Does growth hormone build muscle?

Only modestly and indirectly. Controlled studies show the transient GH rise after a workout does not add muscle or strength beyond the training itself. GH and IGF-1 support tissue repair and connective-tissue growth, but muscle gain is driven by progressive overload, protein and recovery, not by chasing hormone spikes.

How does growth hormone burn fat?

Growth hormone triggers lipolysis: it signals fat cells to release stored triglycerides as free fatty acids that muscle and other tissues burn for fuel. This shifts the body toward using fat during sleep, fasting and long exercise. It supports fat loss but cannot override a calorie surplus.

Does sleep increase growth hormone?

Yes, strongly. The single largest daily GH pulse occurs in the first few hours of deep, slow-wave sleep, and in men roughly 70% of daily output can happen during early sleep. Poor or short sleep blunts this pulse, which is why consistent sleep is central to recovery.

What time is growth hormone highest?

Growth hormone peaks shortly after you fall asleep, during the first cycle of deep slow-wave sleep, usually within the first hour or two of the night. Levels then pulse in smaller bursts through the rest of sleep. This is tied to sleep stage, not the clock time itself.

Do growth hormone supplements work?

Most over-the-counter HGH pills, sprays and amino-acid boosters have little evidence of raising growth hormone or changing body composition. GH is a large peptide destroyed by digestion, so it cannot survive a pill. The proven ways to support GH are deep sleep, hard training and staying lean.

Does fasting increase growth hormone?

Yes. Fasting and low blood sugar raise growth hormone through the stomach hormone ghrelin and reduced insulin, which is why GH climbs overnight and during longer fasts. This helps preserve muscle and shift the body toward burning fat, though the effect on body composition over time is small.

Does growth hormone decline with age?

Yes. GH output is highest during puberty and declines steadily through adult life, a process sometimes called somatopause. This is largely normal aging. Replacing GH in healthy older adults carries real risks such as insulin resistance, fluid retention and joint swelling, and is not recommended as an anti-aging tool.

Are growth hormone injections safe or legal for building muscle?

No. Using prescription GH to build muscle is banned in sport and illegal without a medical indication in most countries. Research shows it adds little real muscle or strength in healthy adults while causing insulin resistance, fluid retention, carpal tunnel symptoms and joint pain. The risks outweigh any benefit.

References

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4. West DW, Phillips SM. Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training. European Journal of Applied Physiology, 2012. PubMed 22105707
5. Hormones, Hypertrophy, and Hype: An Evidence-Guided Primer on Endogenous Endocrine Influences on Exercise-Induced Muscle Hypertrophy. Exercise and Sport Sciences Reviews, 2024. PMC11460760
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8. Yarasheski KE, et al. Effect of growth hormone and resistance exercise on muscle growth in young men. American Journal of Physiology, 1992. PubMed 1550219