Human growth hormone (HGH) does far more than make you grow taller. Produced by a small gland at the base of your brain, it regulates body composition, fat metabolism, bone density, muscle mass, and even mood throughout your entire life. During childhood it drives height, but in adulthood it shifts to a maintenance role, keeping your tissues healthy, your metabolism balanced, and your body repairing itself.
How Your Body Produces HGH
HGH is made in the anterior pituitary gland, a pea-sized structure behind the bridge of your nose. It doesn’t flow steadily. Instead, your brain releases it in pulses controlled by two competing signals from the hypothalamus: one that triggers release and one that suppresses it. This push-and-pull creates a pulsatile secretion pattern, with the biggest bursts happening during deep sleep and after intense exercise. During puberty, these pulses reach their lifetime peak, then gradually decline with age.
Once HGH enters the bloodstream, much of its work is indirect. It travels to the liver and triggers the production of another hormone called IGF-1 (insulin-like growth factor 1). HGH also stimulates IGF-1 production locally in many other tissues. IGF-1 is the main downstream messenger that carries out growth and repair at the cellular level, which is why doctors often measure IGF-1 levels as a more stable indicator of your overall growth hormone activity.
Bone Growth and Skeletal Health
The most visible job of HGH is driving height during childhood and adolescence. It works by stimulating the proliferation and maturation of specialized cells called chondrocytes in the growth plates near the ends of long bones. These cells build new cartilage that gradually mineralizes into bone, lengthening the skeleton. Once the growth plates fuse after puberty, HGH can no longer increase height, but it continues to support bone mineral density and the ongoing turnover of bone tissue.
In adults, the HGH/IGF-1 system regulates skeletal maintenance by promoting the production of the protein matrix that gives bone its structure. When growth hormone levels drop significantly, bone density decreases and fracture risk rises, which is one reason osteoporosis can be a concern in people with growth hormone deficiency.
Fat Metabolism and Body Composition
HGH is one of the body’s key fat-burning signals. It stimulates lipolysis, the process of breaking stored fat into free fatty acids your cells can use for energy. It does this by activating an enzyme in fat tissue, particularly in the visceral fat around your organs and the fat beneath your skin. It also appears to influence proteins on the surface of fat droplets that regulate how readily fat gets mobilized.
At the same time, HGH is anabolic, meaning it promotes the building of lean tissue. It encourages protein synthesis in muscles and other organs, helping maintain or increase muscle mass. This dual action, burning fat while preserving muscle, is why growth hormone deficiency in adults typically shows up as increased belly fat and reduced muscle mass, even when diet and exercise haven’t changed. It also partly explains the interest in HGH among athletes, though its performance-enhancing benefits in healthy adults are far less dramatic than many people assume.
The Sleep and Exercise Connection
Your body’s largest natural HGH pulse happens shortly after you fall asleep, during the first phase of deep slow-wave sleep (stages III and IV). In men, roughly 70% of nighttime growth hormone pulses coincide with slow-wave sleep, and the amount released correlates directly with how much deep sleep occurs. Poor sleep or disrupted sleep patterns can meaningfully reduce this nightly surge.
Exercise provides the other major stimulus. Research shows an intensity threshold exists: working out above the lactate threshold (the point where exercise starts to feel genuinely hard) for at least 10 minutes produces the strongest growth hormone response. Both resistance training and endurance exercise trigger HGH release, with load, intensity, and duration all playing a role. Regular training above this threshold can amplify pulsatile HGH release even at rest, increasing total 24-hour secretion.
Normal Levels Across Age and Sex
Because HGH is released in pulses, a single blood draw captures only a snapshot. Normal ranges, according to Cleveland Clinic reference values, vary considerably:
- Children: 10 to 50 ng/mL
- Adult males: 0.4 to 10 ng/mL
- Adult females: 1 to 14 ng/mL
Children carry much higher baseline levels because they need sustained growth signaling. The wide range in adults reflects the pulsatile nature of secretion: you might test near the low end between pulses and near the high end right after deep sleep or vigorous exercise. Lab reference ranges can also differ slightly between facilities.
What Happens When Levels Are Too Low
Adult growth hormone deficiency is a recognized clinical syndrome, though its symptoms are notoriously nonspecific. The most common features include increased body fat concentrated around the midsection, reduced muscle mass and strength, decreased bone density, and unfavorable cholesterol changes (higher LDL, lower HDL). Cardiovascular risk rises because of accelerated plaque buildup in arteries, impaired heart function, and reduced exercise capacity.
The quality-of-life effects are equally significant. Adults with growth hormone deficiency frequently report persistent fatigue, low energy, depressed mood, increased anxiety, difficulty concentrating, and social withdrawal. These symptoms overlap with many other conditions, which is why diagnosis requires a stimulation test where doctors measure how much HGH the pituitary can produce in response to a challenge rather than relying on a single blood draw alone. A peak response below 3 µg/L on a standard stimulation test is the internationally accepted threshold for severe deficiency.
What Happens When Levels Are Too High
Excess growth hormone in adults causes a condition called acromegaly, most often triggered by a benign pituitary tumor that overproduces HGH. Because adult growth plates are already fused, the extra hormone doesn’t increase height. Instead, it enlarges bones in the hands, feet, and face. The brow becomes more prominent, the jaw widens, and the nose, ears, and lips thicken. Internal organs can also enlarge.
The metabolic consequences are serious. Excess HGH stimulates insulin secretion while simultaneously making cells more resistant to it, which leads to type 2 diabetes in many cases. Cholesterol levels become abnormal. Joint pain and osteoarthritis develop as cartilage and bone remodel in unhealthy ways. Acromegaly also causes sexual dysfunction, irregular menstrual cycles, and infertility. Without treatment, it can become life-threatening due to cardiovascular complications.
Medical Uses of Growth Hormone Therapy
Synthetic growth hormone (recombinant HGH) is an injectable medication with eight FDA-approved uses in children: growth hormone deficiency, Prader-Willi syndrome, being born small for gestational age without catch-up growth, idiopathic short stature, Turner syndrome, SHOX gene deficiency, Noonan syndrome, and chronic kidney insufficiency. In adults, it is approved for treating confirmed growth hormone deficiency, typically caused by pituitary disease, surgery, or radiation.
For people without a diagnosed deficiency, taking synthetic HGH carries real risks. Even at moderate doses, it can cause fluid retention, joint and muscle pain, carpal tunnel symptoms, and insulin resistance. At higher doses or over longer periods, the same complications seen in acromegaly can develop, including heart disease, diabetes, and irreversible bone and tissue changes. Because HGH must be injected, there are also practical risks like blood clots and dosing errors. This is why growth hormone therapy is a prescription treatment intended for specific medical conditions, not a general wellness or anti-aging tool.
Other Roles in Daily Function
Beyond the headline functions of growth, fat metabolism, and muscle maintenance, HGH participates in collagen turnover, which affects skin, tendons, and connective tissue health. It helps regulate fluid balance and body temperature through its effects on sweating and extracellular fluid volume. It also plays a role in immune function and wound healing, which is one reason recovery from injuries can slow as growth hormone levels naturally decline with age.