What one 30-minute heat session did in the lab
A small lab study measured heart rate, blood pressure and a stress protein during a single bout of passive heat. It is not a test of long-term sauna benefits.
The short version
In this small crossover study, 25 healthy young adults sat for 30 minutes in a chamber heated to 73°C, and on another day in a room-temperature control, while researchers measured heart rate, blood pressure and stress markers. During the heat session, heart rate rose to about 131 beats per minute and systolic blood pressure fell by about 16 mmHg, similar to moderate exercise. In the smaller subgroup whose blood was drawn, a stress protein called HSP72 rose, but the result varied widely between people. This was one 30-minute exposure in young, healthy adults, not a test of repeated sauna use.
Keep in mind
A single 30-minute lab exposure in young, healthy adults, not a study of repeated sauna use, and the stress-protein change varied a lot between people.
What they found
During the heat exposure, heart rate rose steadily to an average of about 131 beats per minute, in the range of moderate-intensity exercise for these participants.
Systolic blood pressure fell by about 16 mmHg and diastolic pressure fell by about 5 mmHg during the heat session, consistent with blood vessels widening in response to heat.
In the smaller subgroup with blood draws, HSP72 rose by roughly 49% on average, but individual responses varied enormously: the spread between people was almost as large as the average change itself.
What this means for your practice
This tells us passive heat produces some of the same short-term cardiovascular strain as moderate exercise, which is useful context for how a sauna session feels in the body.
It is not a reason to treat a sauna session as a workout substitute, and it says nothing about what regular sauna use does over months or years.
Methods and limitations
What the researchers did
Twenty-five healthy young adults (13 men, 12 women) sat in a heated chamber at 73°C and, on a separate day, in a room-temperature control, each for 30 minutes. Because each person did both conditions, they served as their own comparison.
Researchers tracked heart rate and blood pressure throughout, and in a smaller subgroup of 13 participants took blood samples to measure a heat shock protein called HSP72, a marker of cellular stress response.
This was a single, acute exposure in a lab setting, not a study of sauna use over weeks or months.
How much can this tell us?
The crossover design, each person compared with themselves, is a real strength for a small study. But 25 people, or as few as 13 for the blood measurements, is not enough to say how reliable or lasting these changes are.
A rise in heart rate and a fall in blood pressure during heat exposure are expected, well-documented thermoregulatory responses, not evidence of a specific health benefit.
A one-off change in a stress protein after a single session says nothing about what happens with repeated sauna use over time, and the wide variability here means the average number should be read cautiously.
What makes it useful
- Crossover design: each person is compared with their own control session
- Includes both men and women
- Directly measured a heat shock protein, not just self-reported feeling
What limits it
- Small sample: 25 for cardiovascular measures, only 13 for the blood/HSP72 measurements
- A single 30-minute session, so it tells us nothing about repeated or long-term use
- The HSP72 change varied so much between people that the average is uncertain
- Young, healthy participants only
Where this study fits
Where this study fits
We score claims, not single studies. This one is part of the evidence for:
Your heart rate rises and blood pressure dips in the sauna. Well supported
High certaintyLarge effectBody signals
Heat switches on protective proteins in your cells. Some support
Low certaintyMedium effectBody signals
Read the original
Iguchi M, Littmann AE, Chang SH, et al. Heat stress and cardiovascular, hormonal, and heat shock proteins in humans. J Athl Train. 2012;47(2):184-190.