Sauna and Growth Hormone: What the Research Shows
Key insights
- In a classic Finnish study, ten men who sat in an 80°C sauna for an hour twice a day saw serum growth hormone rise roughly 16-fold in response to the heat 1.
- The trigger is a rise in core body temperature rather than warm skin: lifting core temperature by about 1°C raised growth hormone more than exercise that produced the same temperature increase, and the response was largest when subjects were fasted 2.
- A three-hour hot bath that raised body temperature by 1.2°C pushed peak growth hormone from about 7 to 56 mU/l — but it arrived alongside a broad stress response of adrenaline, cortisol and free fatty acids 3.
- Heat and exercise each raise growth hormone on their own and act synergistically together; the biggest spike, around 45 ng/mL, occurred when exercise was performed in the heat 4.
- These surges are acute and short-lived — the response faded after the third day of repeated sauna use — and no study shows that sauna-induced growth hormone spikes build muscle or burn fat on their own 1, 4.
Few hormones carry as much mystique as growth hormone. It is marketed as the body's anti-ageing and muscle-building signal, and the claim that a hot sauna can spike it — sometimes by a dramatic-sounding sixteen times — circulates widely in fitness and longevity circles. The figure is real and traces to a genuine study. The question worth asking is what it actually means.
Growth hormone is released by the pituitary gland in pulses, mostly during deep sleep, and it helps regulate tissue repair, metabolism and body composition. Its natural output declines with age, which is partly why anything that reliably raises it attracts attention. Heat exposure is one of the few everyday stimuli shown to do so in controlled human studies.
The human evidence is modest in size but remarkably consistent in direction. Below we look at what the studies found, why heat provokes the response, how large and how durable it is, and how to read the numbers without turning a transient hormone spike into a promise it cannot keep.
What the research actually shows
The headline figure comes from a 1986 study in which ten healthy men and seven women were exposed to dry heat in an 80°C Finnish sauna for one hour, twice a day, for seven consecutive days. In the men, serum growth hormone rose about 16-fold during the heat exposure, while prolactin increased roughly 2.3-fold. Notably, testosterone, thyroid hormones and the gonadotrophins did not change significantly, and cortisol actually edged down — so the growth hormone response was not simply part of a generalised hormonal storm 1.
Two details temper the headline. First, the growth hormone rise declined after the third day, as the body adapted to the repeated thermal load. Second, the authors themselves suggested that part of the increase in growth hormone and prolactin may be linked to heat-induced dehydration rather than a purely anabolic signal. The spike is real, but it is a response to stress and fluid loss as much as to heat alone 1.
Why heat triggers a growth hormone spike
The clearest mechanistic work actually predates the sauna study. In a 1984 experiment, researchers raised volunteers' core temperature by about 1°C using heated water blankets and measured the growth hormone response. The rise was substantial — and, crucially, larger than that produced by exercise generating the same temperature increase. When the same exercise was performed in a cold room so that core temperature could not climb, the growth hormone response was abolished entirely. It is the rise in core temperature, not warm skin, that the body responds to 2.
The same study revealed a practical lever: fasting amplified the effect. Growth hormone climbed to a mean of about 18 ng/ml when subjects were fasted, against roughly 8 ng/ml when they had eaten beforehand. In other words, the pituitary's response to heat is gated by the body's metabolic state, which helps explain why results vary between individuals and from one session to the next 2.
How big is the effect — and how long does it last?
Passive heating outside the sauna produces the same pattern. In a study of six men, a three-hour hot bath that raised core temperature by 1.2°C lifted peak growth hormone from about 7 to 56 mU/l. But the researchers' framing is instructive: the hot bath also raised adrenaline, glucagon, cortisol and free fatty acids, leading them to describe hyperthermia as mimicking the hormonal and metabolic picture of a mild infection. The growth hormone surge, in this light, is one thread in a whole-body stress response 3.
More recent work confirms that heat and exercise are each sufficient to raise growth hormone, and that combining them is synergistic: the largest increase, about 45 ng/mL, occurred when subjects exercised in hot conditions. That study also recorded a fall in plasma volume during heat — a reminder that some haemoconcentration accompanies these measurements. As for duration, the repeated-sauna data is the best guide: the response is acute, peaking around a session and tapering across days of habitual exposure 4.
Realistic expectations
It is worth being clear about what these numbers do not establish. The spikes are transient, lasting minutes to hours, and they sit inside a broader stress and fluid-loss response rather than acting as a clean anabolic command. Acute pulses of growth hormone are also physiologically different from the sustained, supraphysiological levels produced by medical growth hormone therapy 3.
No controlled trial has shown that sauna-induced growth hormone spikes translate into measurable muscle gain, fat loss or slowed ageing on their own. The studies are also small — six to seventeen subjects — and concentrated in men. The sensible interpretation is that a growth hormone rise is a reliable marker of the body's response to heat stress, not a shortcut to body recomposition 1, 4.
How to use heat if growth hormone is the goal
The mechanism points to a few evidence-led principles. Because the trigger is a genuine rise in core temperature, what matters is reaching and holding a true thermal load — a traditional sauna hot enough, and a session long enough, to raise core temperature rather than merely warm the skin. Fasted sessions appear to amplify the response, so heat taken before a meal may produce a larger rise than one afterwards 2.
Temper that with the physiology of the stress response. The same studies that record growth hormone surges also record fluid loss and rising stress hormones, so rehydrate, cool down gradually, and avoid chasing ever longer or hotter sessions in pursuit of a bigger number. Heat's hormonal effects also extend beyond growth hormone — for the wider picture, see our companion piece on sauna and testosterone.
The Contrast Market Perspective
The thread running through this research is that the response depends on core temperature — which means it depends on a sauna that actually reaches its target heat and holds it steadily for the length of a session. An underpowered or inconsistent unit warms the skin without delivering the thermal load these studies relied on, and the hormonal response scales with that load. Precision is the point, not a luxury. If you want equipment built to produce a reliable, repeatable thermal stimulus, Schedule a consultation and we will help you match the sauna to your goals.
References
The primary studies cited above are listed in full below.
Footnotes
- Leppäluoto J, Huttunen P, Hirvonen J, Väänänen A, Tuominen M, Vuori J (1986). Endocrine effects of repeated sauna bathing. Acta Physiologica Scandinavica. PubMed ↩︎
- Christensen SE, Jørgensen OL, Møller N, Orskov H (1984). Characterization of growth hormone release in response to external heating: comparison to exercise induced release. Acta Endocrinologica (Copenhagen). PubMed ↩︎
- Møller N, Beckwith R, Butler PC, Christensen NJ, Orskov H, Alberti KG (1989). Metabolic and hormonal responses to exogenous hyperthermia in man. Clinical Endocrinology (Oxford). PubMed ↩︎
- Ftaiti F, Jemni M, Kacem A, Zaouali MA, Tabka Z, Zbidi A, Grélot L (2008). Effect of hyperthermia and physical activity on circulating growth hormone. Applied Physiology, Nutrition, and Metabolism. PubMed ↩︎