Growth Hormone: How You Grow (and Why It Stops)

A child becomes an adult twice their size — and then, one day, stops growing. The engine is a relay: the brain tells the pituitary to fire growth hormone (GH) in pulses, GH tells the liver to make IGF-1, and IGF-1 drives the growth plates in your long bones to lengthen. Press play and watch a GH pulse ripple down that chain, the bone climb the ruler — and then, at puberty, the growth plates fuse shut. Once they are gone, no hormone on earth can make you taller.

Try this: start on Child and watch the height climb, then switch to Puberty and wait for the growth plate to seal (you will hear a soft thud). Finally hit Too much GH to see gigantism turn into acromegaly.

The Science in Plain Language

Two switches in the brain: one says “go,” one says “stop”

Growth hormone is not poured out steadily — it comes in bursts. Deep in the brain, the hypothalamus controls the pituitary gland (a pea-sized gland just behind the bridge of your nose) with two opposing signals. GHRH (growth-hormone-releasing hormone) tells the pituitary to fire; somatostatin tells it to hold. The tug-of-war between them produces roughly ten pulses of GH a day. Between pulses, the blood level can sit below 1 ng/mL; during a pulse it can spike to 10–30 ng/mL and then fall again within an hour. The single biggest pulse usually comes about an hour after you fall into deep (slow-wave) sleep, with smaller surges after vigorous exercise and during fasting. This is why a one-off GH blood test is nearly useless: catch it at a trough and it looks like zero; catch it at a peak and it looks sky-high.

GH barely grows you — it delegates the job to the liver

Here is the twist most people never hear: growth hormone does very little growing by itself. Instead it travels to the liver and orders it to manufacture a second hormone, IGF-1 (insulin-like growth factor 1). IGF-1 is the actual foreman on the building site — it is the messenger that reaches your tissues and tells them to divide and enlarge. Because IGF-1 is steady and long-lasting (it rides through the blood bound to carrier proteins), it smooths out those jerky GH pulses into one dependable signal. That is exactly why doctors test IGF-1, not GH, when they want to know whether the growth axis is running too hot or too cold: IGF-1 is a running average of the whole day's GH.

The growth plate: where height actually comes from

Your height is built at the growth plates (epiphyseal plates) — thin bands of cartilage near each end of your long bones, such as the thigh bone and shin. Inside the plate, cartilage cells called chondrocytes line up in columns and do two things over and over: they divide, and then they swell and die, leaving a scaffold that hardens into new bone. This process — cartilage steadily replaced by bone — is called endochondral ossification, and it pushes the bone ends apart. In the animation, every time a chondrocyte divides you hear a soft pop and the bone climbs the ruler by a fraction. A young child grows fast (a baby adds about 25 cm in the first year), then settles to a steady 5–6 cm a year through childhood.

Inside the growth plate: an assembly line, zone by zone

The little cells pulsing in the diagram are a simplification of a beautiful, orderly factory. A real growth plate is stacked in four zones, and cartilage flows through them like an assembly line. At the top sits the resting (reserve) zone, a quiet stock of stem-like chondrocytes. Just below, in the proliferative zone, those cells divide furiously and stack into neat vertical columns — this is the actual dividing that IGF-1 drives, and it is what lengthens the bone. Next the cells enter the hypertrophic zone, where each chondrocyte swells to many times its size and then dies, leaving behind a calcified scaffold. Finally, in the zone of ossification, blood vessels and bone-building cells (osteoblasts) invade that scaffold and lay down real bone. Cartilage in at the top, bone out at the bottom — and the bone gets a little longer with every pass. The plate stays the same thickness the whole time; it simply keeps moving away from the shaft as new bone piles up beneath it.

Why you stop: puberty seals the plates shut

Growth does not gently taper to nothing — it is actively switched off. At puberty, the sex hormones (especially estrogen, which matters in both boys and girls) first drive a dramatic growth spurt — peak velocity is roughly 9 cm/year in boys and 8 cm/year in girls — and then those same hormones cause the growth plates to fuse. The cartilage is entirely converted to bone; the plate simply disappears. Once that happens, there is no cartilage left for IGF-1 to act on, so you cannot get taller, no matter how much GH you have. Plates typically close in the mid-teens, a year or two earlier in girls than in boys. Watch for the moment in the Puberty scenario when the plate turns to bone and the height freezes for good.

GH has a day job too: fat, fuel and blood sugar

Even after you stop growing, GH keeps working — on metabolism. It signals fat cells to release stored fat for fuel (lipolysis), and it opposes insulin, nudging your blood sugar upward so more glucose is available to muscles and brain. In healthy amounts this is useful. But it is the reason chronic GH excess causes trouble with blood sugar: watch the glucose readout climb in the “Too much GH” scenario. In acromegaly, insulin resistance is common and a substantial minority of patients develop type 2 diabetes.

Too little GH: short stature you can treat

If a child's pituitary makes too little GH, IGF-1 stays low and the growth plates, though open, are barely driven — the child grows slowly and ends up short (GH deficiency). The good news is that this is one of the most treatable of all hormone problems: daily injections of recombinant human growth hormone (somatropin) can restore a normal growth rate and, if started early enough, a normal adult height. Toggle GH deficiency in the diagram to watch IGF-1 collapse and the height stall — then imagine the injections filling the gap back in. (Not every short child is GH-deficient; most are simply on the low end of normal and need no treatment at all.)

Too much GH: gigantism before the plates close, acromegaly after

Usually the cause is a benign pituitary tumour that pumps out GH nonstop. The same excess produces two completely different pictures depending on timing. In a child whose plates are still open, the bones keep lengthening far past normal — gigantism. The tallest well-documented person, Robert Wadlow, reached about 272 cm (8 ft 11 in) from an untreated pituitary tumour. But once the plates have fused, the bones can no longer grow longer, so they grow thicker and coarser instead — acromegaly: enlarging hands and feet (rings and shoes stop fitting), a jutting jaw and heavy brow, thickened skin, and often headaches, sweating and joint pain. Doctors confirm it by finding a high IGF-1 and, on an oral glucose tolerance test, GH that fails to suppress (in a healthy person a sugary drink drops GH below about 1 ng/mL). Treatment is surgery to remove the tumour, plus medicines like the somatostatin analogues octreotide and lanreotide, or pegvisomant, which blocks the GH receptor.

The myth: GH is not a “fountain of youth”

Growth hormone is heavily marketed as an anti-ageing miracle, and it is abused in sport. The evidence does not support the hype. A small 1990 study in older men found GH shifted body composition a little — slightly more lean mass, slightly less fat — and that single finding launched a whole industry. But later, larger reviews of the research found the same story every time: in healthy adults, GH produces modest changes in appearance with no proven gain in strength, stamina or quality of life, and a high rate of side effects — fluid retention, joint pain, carpal-tunnel symptoms, and worsened blood sugar. In sport, GH is banned, hard to detect, and its performance benefit is largely unproven. The honest summary: your body already knows exactly how much GH to make and when. Chronic excess is not youth — it is a slow drift toward acromegaly, and acromegaly shortens lives. The natural ways to support healthy GH are unglamorous and free: get deep sleep, exercise, and avoid the constant high blood sugar that blunts your own pulses.

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Connections

• All Interactive Visualizations
• How Your Thyroid Is Controlled
• Bone Remodeling & Calcium
• Acromegaly
• Endocrinology