Thirty hot-water sessions left blood pressure unchanged in untreated hypertension
In this 2025 Journal of Applied Physiology trial, 41 adults with untreated high blood pressure got either hot-water immersion or aerobic exercise, and neither brought their pressure down.
The paper
No effect of either heat therapy or aerobic exercise training on blood pressure in adults with untreated hypertension: a randomized clinical trial
Kaiser BW, Comrada LN, Gibson BM, Reed EL, et al.. Journal of Applied Physiology, 2025;138(6):1600-1614.
See the study at a glance
- Design
- Randomized trial of heat therapy against exercise
- People
- 41 adults
- Who they were
- The participants were middle-aged adults in Oregon whose high blood pressure wasn't being treated.
- What they did
- Both groups had 30 supervised sessions over 8–10 weeks. The heat group sat in 40°C water up to mid-chest for 45 minutes, and a fan came on if core temperature passed 38.5°C. The exercise group cycled.
- How long
- 8–10 weeks
These numbers came out of it
134 → 134
Heat therapy left 24-hour systolic blood pressure (the top number, in mmHg) exactly where it started.
139 → 140
With exercise training, 24-hour systolic pressure barely moved.
81 → 81
24-hour diastolic pressure (the bottom number) stayed put with heat therapy.
The researchers did this
The Oregon team expected heat therapy to lower blood pressure more than exercise. They randomly assigned 41 adults with untreated hypertension to 30 sessions of either hot-water immersion or supervised cycling over eight to ten weeks.Source 1 · Randomized trialNo effect of either heat therapy or aerobic exercise training on blood pressure in adults with untreated hypertension: a randomized clinical trialKaiser BW, Comrada LN, Gibson BM, et al.. Journal of Applied Physiology, 2025.Read the paper ↗PubMed ↗
Each heat session was 45 minutes in 40°C water up to mid-chest, and a fan came on if core temperature went above 38.5°C. The main outcomes were blood pressure in the clinic and blood pressure over 24 hours on a portable monitor.Source 1 · Randomized trialNo effect of either heat therapy or aerobic exercise training on blood pressure in adults with untreated hypertension: a randomized clinical trialKaiser BW, Comrada LN, Gibson BM, et al.. Journal of Applied Physiology, 2025.Read the paper ↗PubMed ↗
Neither treatment moved blood pressure. Twenty-four-hour systolic pressure was 134 mmHg before and after heat, and it went from 139 to 140 with exercise. Diastolic and clinic readings stayed flat too, and the groups ended up alike on artery stiffness and kidney markers.Source 1 · Randomized trialNo effect of either heat therapy or aerobic exercise training on blood pressure in adults with untreated hypertension: a randomized clinical trialKaiser BW, Comrada LN, Gibson BM, et al.. Journal of Applied Physiology, 2025.Read the paper ↗PubMed ↗
The study can't tell you these things
- There was no untreated control group, so the trial compares two treatments that both came up empty.
- The heat was hot-water immersion. In a head-to-head test, a traditional sauna raised core temperature less than hot water did.Source 2 · Crossover trialComparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalitiesAtencio JK, Reed EL, Wiedenfeld Needham K, et al.. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2025.Read the paper ↗PubMed ↗
- Participants knew which treatment they'd been given.
- A trial of 41 people could have missed a small effect.
People quote it like this
The result cuts against the idea that heat works like a blood pressure treatment. It comes from the same Oregon lab that reported large vascular gains in sedentary young adults in an earlier hot-water study.Source 3 · Clinical trialPassive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humansBrunt VE, Howard MJ, Francisco MA, et al.. The Journal of Physiology, 2016.Read the paper ↗PubMed ↗
We cited these sources
- 01Kaiser BW, Comrada LN, Gibson BM, Reed EL, Abbotts KSS, Larson EA, et al.. No effect of either heat therapy or aerobic exercise training on blood pressure in adults with untreated hypertension: a randomized clinical trial. Journal of Applied Physiology. 2025;138(6):1600-1614. doi:10.1152/japplphysiol.00959.2024 PMID 40407037
- 02Atencio JK, Reed EL, Wiedenfeld Needham K, Lucernoni KM, Comrada LN, Halliwill JR, et al.. Comparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalities. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. 2025;329(1):R20-R35. doi:10.1152/ajpregu.00012.2025 PMID 40332494
- 03Brunt VE, Howard MJ, Francisco MA, Ely BR, Minson CT. Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans. The Journal of Physiology. 2016;594(18):5329-5342. doi:10.1113/JP272453 PMID 27270841