Growth hormone is one of the most influential hormones in your body, affecting everything from how tall you grow as a child to how you burn fat, build muscle, and maintain bone strength as an adult. Produced by the pituitary gland at the base of your brain, it works both directly on tissues and indirectly by triggering the liver to produce a second hormone called IGF-1, which carries out many of its effects throughout the body.
How Growth Hormone Signals the Body
The pituitary gland releases growth hormone in pulses rather than a steady stream. Two competing signals from the brain control this rhythm: one hormone stimulates release, and another (somatostatin) suppresses it. The result is a pulsing pattern of secretion that fluctuates throughout the day, with the largest bursts happening during deep sleep. In men, 60% to 70% of total daily growth hormone output occurs during early sleep, specifically during the deep, slow-wave stages of non-REM sleep. This is one reason disrupted or insufficient sleep can meaningfully lower growth hormone levels over time.
Once released into the bloodstream, growth hormone binds to receptors on cells throughout the body. In the liver, this binding triggers production of IGF-1, which then circulates and acts on tissues including bone, muscle, and cartilage. Interestingly, insulin plays a gatekeeper role in this process. Insulin increases the number of growth hormone receptors on liver cells, making the liver more responsive. In effect, insulin decides whether growth hormone is allowed to generate IGF-1 production. This interplay between growth hormone and insulin has wide-ranging consequences for metabolism.
Driving Bone Growth and Density
The most visible job of growth hormone is making children grow taller. It does this by stimulating the growth plates (epiphyseal plates) at the ends of long bones, where new cartilage cells multiply and gradually harden into bone. Growth hormone directly promotes the proliferation of the precursor cartilage cells, while IGF-1 pushes those cells to mature and differentiate. Together, they lengthen bones until the growth plates fuse, typically in the late teens.
Growth hormone’s role in bone doesn’t stop after you finish growing. In adults, it supports bone density by stimulating the cells that build new bone tissue (osteoblasts) and by reducing the rate at which those cells die off. It also influences parathyroid hormone, which further boosts local IGF-1 production inside bone. This creates a cycle that supports ongoing bone remodeling. When growth hormone levels drop significantly in adults, bone mineral density declines, increasing the risk of fractures.
Breaking Down Fat
Growth hormone is one of the body’s primary fat-burning signals. It reduces body fat through two mechanisms: it slows the creation of new fat (lipogenesis) and accelerates the breakdown of stored fat (lipolysis). This lipolytic effect has been documented in humans, mice, rats, and cattle.
The way growth hormone breaks down fat is more nuanced than it first appears. Rather than acting directly on fat cells to trigger fat release, growth hormone appears to amplify the fat-burning effects of other hormones, particularly adrenaline and noradrenaline. Research shows that growth hormone significantly improves how well fat cells respond to adrenaline’s signal to release stored fatty acids. The freed fatty acids then become available as fuel, effectively shifting the body’s energy source away from glucose and protein and toward fat. This is why people with growth hormone deficiency tend to accumulate fat around the midsection, and why restoring normal levels improves body composition.
Building and Preserving Muscle
Growth hormone promotes muscle maintenance primarily by redirecting how your body uses amino acids, the building blocks of protein. Normally, a portion of the amino acids you consume gets burned for energy (oxidized) rather than used to build tissue. Growth hormone shifts that balance, channeling more amino acids toward protein synthesis and away from being burned as fuel. The net result is a more favorable protein balance in the body.
Studies measuring amino acid flow across forearm muscles have shown that growth hormone increases the rate of protein synthesis without necessarily slowing protein breakdown. This is different from insulin and IGF-1, which preserve muscle in part by reducing breakdown. The practical effect is that adequate growth hormone helps you maintain lean muscle mass, while a deficiency makes it notably harder to build or keep muscle, even with exercise. Patients with growth hormone deficiency commonly report lack of muscle tone and an inability to build muscle despite effort.
Effects on Blood Sugar
Growth hormone has a complicated relationship with blood sugar. It acts as a counter-regulatory hormone to insulin, meaning it works in the opposite direction. It raises blood glucose by promoting the liver’s production of new glucose (gluconeogenesis) and by releasing stored glucose from the liver (glycogenolysis). It also reduces how effectively insulin clears sugar from the bloodstream, creating a mild form of insulin resistance.
This anti-insulin effect is why growth hormone therapy can temporarily worsen insulin sensitivity, particularly during the first months of treatment. In practice, fasting blood sugar and long-term glucose markers like HbA1c typically remain within normal ranges, but the body compensates by producing more insulin. Over time, glucose tolerance often improves as the body adjusts. The fat-burning effects of growth hormone also help indirectly, since less abdominal fat generally means better insulin sensitivity. Still, this push-pull between growth hormone and insulin is one reason doctors monitor blood sugar during growth hormone therapy.
What Happens When Levels Are Too Low
Growth hormone deficiency in children causes the most obvious symptom: slowed or stalled growth, resulting in short stature. In adults, the picture is subtler and often goes undiagnosed because the symptoms overlap with so many other conditions. Adults with growth hormone deficiency typically experience increased abdominal fat, fatigue, general weakness, reduced bone density, and difficulty building muscle. Psychological effects are also common, including cognitive impairment (feeling scattered, difficulty retaining information), lack of motivation, social withdrawal, and depression.
Cardiovascular risk also rises with growth hormone deficiency. The combination of increased abdominal fat, unfavorable cholesterol profiles, and reduced cardiac function contributes to a higher risk of heart disease. Some patients with severe, untreated deficiency face reduced life expectancy. Diagnosis involves a stimulation test where a substance is given to provoke growth hormone release, and blood levels are then measured. A normal response is a peak above 5 ng/mL in children (with some experts requiring above 8 ng/mL to be considered clearly normal) and above 4 ng/mL in adults. Levels below these thresholds during stimulation confirm deficiency.
Approved Medical Uses
Synthetic growth hormone (recombinant human growth hormone) is FDA-approved for a specific set of conditions. In children, it is used to treat growth failure caused by growth hormone deficiency, Turner syndrome, chronic kidney disease (up to the point of a kidney transplant), and idiopathic short stature, defined as a height more than 2.25 standard deviations below the mean with growth plates that haven’t yet closed.
In adults, it is approved as replacement therapy for those with confirmed growth hormone deficiency, whether it originated in childhood or developed later due to pituitary disease, brain surgery, radiation therapy, or trauma. Treatment in adults leads to increased bone density and muscle mass, improved cardiac and metabolic function, better body composition, and improved quality of life. These benefits reflect a reversal of the symptoms that deficiency causes, reinforcing how central growth hormone remains to normal body function well beyond childhood.