Growth hormone is a protein produced by your pituitary gland, a pea-sized structure at the base of your brain. It regulates growth throughout childhood, increasing bone length, bone density, and muscle mass. But its job doesn’t end when you stop growing. In adults, growth hormone continues to manage how your body breaks down fat, processes carbohydrates, and maintains healthy body composition for the rest of your life.
How Growth Hormone Works in Your Body
The pituitary gland releases growth hormone in pulses throughout the day, with the largest bursts happening during deep sleep. Once in the bloodstream, growth hormone travels to the liver and other tissues, where it triggers the production of a second messenger called insulin-like growth factor-1 (IGF-1). Most of the hormone’s effects on your bones, muscles, and organs are carried out through IGF-1.
In children and adolescents, the primary job is building the skeleton. Growth hormone signals specific cells in cartilage (chondrocytes) and bone (osteoblasts) to multiply faster, which is how bones lengthen and thicken during puberty. After growth plates close in late adolescence, the hormone shifts its focus to maintenance: regulating blood sugar, supporting lean muscle mass, and helping the body use stored fat for energy.
What Controls Growth Hormone Release
Your body doesn’t release growth hormone at a constant rate. A network of signals turns the faucet on and off. Two key players originate in the hypothalamus, the brain region sitting just above the pituitary. One signal, called growth hormone-releasing hormone (GHRH), tells the pituitary to secrete more. Another, somatostatin, acts as the brake, suppressing release. The rhythm of growth hormone pulses depends largely on the push and pull between these two.
A third signal comes from the gut. Ghrelin, the “hunger hormone,” stimulates growth hormone release through multiple routes: it acts directly on pituitary cells, it counteracts somatostatin’s suppressive effect, and it encourages the hypothalamus to produce more GHRH. Meanwhile, IGF-1 itself feeds back to slow things down, both by acting on the pituitary directly and by triggering somatostatin release. This feedback loop keeps levels in a healthy range.
Sleep, Exercise, and Natural Levels
Sleep is the single biggest driver of daily growth hormone output. The largest pulses occur during deep, non-REM sleep early in the night. Research from UC Berkeley has shown that both somatostatin and GHRH surge during REM sleep to boost growth hormone, while during non-REM sleep the balance shifts: somatostatin drops and GHRH rises moderately. Chronic sleep deprivation lowers growth hormone levels, though the precise mechanism behind the non-REM connection is still being studied.
High-intensity exercise also triggers substantial growth hormone release, which is one reason resistance training supports muscle growth and bone health. Fasting and drops in blood sugar can stimulate release as well. On the flip side, high body fat, especially around the midsection, is associated with lower baseline levels.
Normal Growth Hormone Levels by Age
Growth hormone levels are highest during childhood and puberty, then decline steadily. According to reference ranges from Mayo Clinic Laboratories, here’s what typical blood levels look like:
- Children ages 2 to 6: 0.05 to 5.11 ng/mL
- Children ages 7 to 11: 0.02 to 4.76 ng/mL
- Adolescents ages 12 to 13: 0.02 to 6.20 ng/mL
- Teen boys ages 14 to 17: 0.02 to 3.81 ng/mL
- Teen girls ages 14 to 17: 0.03 to 5.22 ng/mL
- Adult men (18+): 0.02 to 0.97 ng/mL
- Adult women (18+): 0.02 to 3.61 ng/mL
Because growth hormone is released in pulses, a single blood draw can catch a peak or a trough. That’s why doctors typically rely on stimulation tests or IGF-1 measurements rather than a single snapshot to evaluate whether levels are truly abnormal.
What Happens When Levels Are Too Low
Growth hormone deficiency (GHD) can be present from birth or develop later in life due to pituitary tumors, head injuries, or radiation therapy. In children, the hallmark sign is falling behind on the growth chart. After age three, a child growing less than about 1.4 inches per year may warrant evaluation. Other signs in children include a younger-looking face for their age, delayed tooth development, slow hair and nail growth, delayed puberty, and episodes of low blood sugar in infants and toddlers.
Adults with GHD experience a different set of problems. Because the hormone’s adult role centers on metabolism and body composition, deficiency tends to show up as increased belly fat, decreased muscle tone, reduced bone density (raising osteoporosis risk), higher LDL cholesterol and triglycerides, insulin resistance, low energy, and symptoms of anxiety or depression. Many adults describe it as a general loss of well-being that’s hard to pin down until hormone levels are tested.
What Happens When Levels Are Too High
Excess growth hormone is almost always caused by a benign pituitary tumor that overproduces the hormone. The consequences depend on when it starts. In children whose growth plates haven’t yet fused, the result is gigantism, an extreme increase in height because bones can still lengthen. In adults, the same overproduction causes acromegaly, where bones can no longer grow longer but cartilage, organs, and soft tissues enlarge. Hands and feet widen, facial features become coarser, and the jaw may protrude forward.
Acromegaly develops slowly, often over years, so many people don’t notice the gradual changes. A high IGF-1 level on a blood test is typically the first clue. To confirm the diagnosis, doctors use a glucose tolerance test: drinking a sugary solution should suppress growth hormone levels, and if they don’t fall enough, acromegaly is confirmed.
Medical Uses of Synthetic Growth Hormone
Recombinant human growth hormone (a lab-made version identical to the natural protein) is FDA-approved for several conditions. In children, approved uses include growth hormone deficiency, Turner syndrome, Noonan syndrome, Prader-Willi syndrome, chronic kidney insufficiency, being born small for gestational age, and idiopathic short stature (short stature with no identifiable cause). In adults, it’s used primarily for confirmed growth hormone deficiency, including patients transitioning from childhood-onset deficiency into adult care.
Treatment involves daily or weekly injections, and the goal in children is to normalize growth velocity rather than reach a specific height. In adults, the aim is to restore metabolic balance: improving body composition, bone density, energy, and cholesterol profiles.
Side Effects of Growth Hormone Therapy
When prescribed for a genuine deficiency, growth hormone therapy is generally well tolerated, but it does carry risks. The most common side effects include joint and muscle pain, high blood sugar, and in some cases progression toward type 2 diabetes. These risks are dose-dependent and tend to be more pronounced in adults using growth hormone without a medical need, such as for anti-aging purposes or athletic performance, where the hormone is being added on top of already-normal levels.
The Mayo Clinic notes that there is no reliable evidence that growth hormone therapy slows aging in healthy adults, and the side effect profile makes off-label use a poor trade-off for most people.