Heat shock proteins: what they do, and why sauna induces them

What it means

Heat shock proteins (HSPs) are a family of molecular chaperones — HSP70 and HSP90 are the best known — that bind to misfolded or damaged proteins and either refold them or tag them for disposal. They are present at a baseline level in every cell and sharply upregulated by stress: heat, exercise, fasting, oxidative stress, ischaemia. The response is a classic case of hormesis.

Protein misfolding and aggregation accumulate with age and underlie neurodegeneration; HSP induction is one of the body's defences against that, and the response weakens with age.

Why it matters for longevity

Raising HSP expression extends lifespan in worms and flies and protects the heart and brain in rodent models of injury. In humans, the interest is in whether repeated heat exposure — sauna — produces a sustained rise in HSPs that explains the cardiovascular and dementia associations seen in the Finnish cohorts, and whether it can partly stand in for exercise in people who cannot train.

What the evidence says

Human studies show HSP70 rises in blood and muscle after a 30-minute sauna at 80–100°C or after hot-water immersion, with larger responses after repeated sessions. Hoekstra 2018 and Brunt 2016 found that passive heating improved vascular function and glucose handling in sedentary adults, consistent with an HSP and nitric-oxide mechanism.

The outcome data come from the Kuopio cohort (Laukkanen 2015, 2,300 Finnish men, 20 years): four to seven sauna sessions a week versus one was associated with about 40% lower all-cause mortality and 65% lower dementia risk. It is observational — people who sauna seven times a week differ in many ways — but the dose-response and the mechanism make it one of the better-supported associations in the field.

How to measure or use it

• HSPs are a research measure; there is no routine test. The proxies are the outcomes: blood pressure, resting heart rate and HRV over eight weeks.
• The Finnish dose: 15–20 minutes at 80–100°C, two to four times a week, with cooling and fluids. Hot-water immersion at 40°C for 20–30 minutes produces a similar HSP response.
• Timing: sauna after strength training is fine and may help; cold after it blunts the adaptation.

Related

• Sauna and heat — the full therapy page, graded
• Inflammation and immunity — the inflammation link
• Sleep and longevity — evening heat and sleep onset