Sauna and growth hormone: what the study found

"Sauna raises growth hormone 16-fold" is one of the most repeated lines in sauna marketing. It comes from a real Finnish study from 1986. Read the paper and the number looks rather different: the protocol was extreme, the effect faded within days, and nobody measured whether it did anything useful.

The 1986 Finnish study

The paper, by Leppäluoto and colleagues, was published in Acta Physiologica Scandinavica in 1986 under the title "Endocrine effects of repeated sauna bathing". Here is what the researchers did:

• Who: ten healthy men and seven healthy women. The women were only included in the prolactin measurements, so the growth hormone results are from ten men.
• The heat: a Finnish sauna at 80 °C, for one hour, twice a day, for seven days in a row.
• What they measured: a panel of hormones in the blood, plus stress hormones in the urine, before the experiment and on days one, three and seven.

And here is what they found:

• Growth hormone rose about 16-fold in the men, and prolactin about 2.3-fold. In the women, prolactin rose more than fourfold.
• The growth hormone response declined after the third day. The body adapted.
• Testosterone, thyroid hormones and the hormones that tell the testes to work didn't change significantly. Cortisol fell slightly.
• Five of the seven women had a temporary missed period after the experiment, which the authors linked to the high prolactin.

The authors also suggested that the rise in prolactin, and perhaps growth hormone, may have been linked to dehydration from all that heat. Two hours a day at 80 °C is a lot of sweat.

What other studies found

The same Finnish researchers and others followed up with shorter, more normal sessions:

• 1987, 15 minutes at 72 °C (162 °F). In six men aged 31 to 46, growth hormone rose from 2 to 5 micrograms per litre 30 minutes after the session. In six men aged 49 to 66, there was no significant rise at all.
• 1989, three sessions in eight young men. Growth hormone rose at 100 °C (212 °F), staying in until they felt uncomfortable. At 80 °C, the more usual temperature, it wasn't among the hormones that rose.

So with a 15-minute session the rise was about two and a half times, at 80 °C one study saw none, and the older men didn't respond at all. That's a long way from the 16-fold headline.

Why the big multiples mislead

Growth hormone isn't released in a steady stream. It comes in bursts, with long stretches in between where levels in the blood are very low. In many healthy adults, the biggest burst of the day comes soon after you fall asleep, during deep sleep.

That has two consequences for the sauna figures:

1. A low starting point makes multiples look huge. If you start from close to zero, a modest rise can be a big multiple. "16 times higher" tells you the ratio, not whether the level ended up anywhere unusual for a healthy body.
2. It's a short spike. The studies measured blood levels around the session. A brief rise during or after a hot hour isn't the same as more growth hormone across the whole day or week.

Then there's the adaptation. If the rise shrinks after three days of sessions, the regular sauna user, the person most interested in the claim, may be the one who gets the least out of it.

What nobody measured

None of these studies measured muscle mass, strength, fat loss, recovery, skin or anything to do with ageing. They measured a hormone in the blood. Going from "this hormone went up" to "the sauna builds muscle and slows ageing" is a leap the research doesn't make.

Growth hormone also isn't simply "more is better". Too much of it over many years causes a medical condition called acromegaly. The useful question is whether your body makes enough, and that's a question for a doctor and a blood test.

So is a sauna good for muscle?

There's no evidence that the sauna's effect on growth hormone builds muscle. There is some evidence that a sauna after training can help endurance and make you feel less stiff, though the studies are small. Our guide on sauna before or after a workout goes through it.

If building muscle is your goal, the things that work are well known: progressive strength training, enough protein, and enough sleep, which is when your body's own biggest growth hormone burst happens. A sauna can be a pleasant part of that routine. It isn't a shortcut. For a balanced look at what heat does, see sauna benefits, and for the related hormone claim, does a sauna boost testosterone?

Who should be careful

Don't try to copy the 1986 protocol. An hour at 80 °C, twice a day, is far beyond a normal session and risks dehydration and heat illness. Most people do rounds of 10–20 minutes with breaks, as explained in how long to stay in a sauna.

Check with a doctor first if you have a heart condition, unstable blood pressure, are pregnant or take medicine that affects blood pressure or sweating. Never use a sauna after drinking alcohol, and leave if you feel dizzy, sick or confused.

This guide is general information, not medical advice.

Where to find a sauna

Find My Sauna lists 2,616 places with a Finnish-style sauna. These cities have the most:

RING Spaa & Saunad

Tallinn · Sauna centre

Aura Keskus

Tartu · Pool and saunas

Tallinn Viimsi SPA

Tallinn · Spa and saunas

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