Do Hot Baths Sharpen the Ageing Brain?
Twelve older adults took hour-long 40 °C soaks for six weeks. Two thinking tests improved, but the main memory test did not.
In one paragraph
A small trial asked whether repeated hot baths improve thinking in healthy older adults. Twelve people (average age 69.2) soaked in 40 °C water for 60 minutes, two to three times a week for 6 weeks. Logical reasoning rose from 22.48 to 25.31 correct responses per minute and a simple memory test from 67.92 to 73.96, but the planned main memory test did not change (53 vs 55). With no control group and only 12 people, practice effects cannot be ruled out, so the evidence is limited.
How did researchers test hot baths on the ageing brain?
Researchers in the UK recruited healthy adults aged 55 or over without heart, metabolic or neurological disease. Of 19 recruited, 12 completed the study; their average age was 69.2 and 8 were women.
For 6 weeks, participants had two to three sessions a week of immersion to just below the shoulders in 40 °C water for 60 minutes. Core (rectal) temperature was held at 38.5–39.0 °C by lifting people partly out of the water or back in. On average they completed 16 ± 2 sessions.
Before, right after and 3 h after the first and final sessions, participants did computerised tests of reaction time, logical reasoning and working memory (the 1-back and the harder 2-back, where each item is compared with the one shown two steps earlier). A forehead light sensor tracked oxygen in the front of the brain. Neck artery blood flow, a week of sleep from a wrist tracker, and blood markers linked to Alzheimer's disease were measured before and after the 6 weeks.
Did hot water immersion improve memory and reasoning?
The planned primary outcome, 2-back working memory right after bathing, did not change between the first and final sessions (53 vs 55 correct responses per minute, P = 0.321).
Two secondary tests did improve. Logical reasoning rose from 22.48 to 25.31 correct responses per minute (P = 0.02), and the simpler 1-back memory test from 67.92 to 73.96 (P = 0.026). Reaction time did not improve.
The proposed explanation, more oxygen reaching the brain, was not supported. Straight after a bath, brain oxygenation fell briefly and returned to baseline 3 h later, while a single bath gave a short-term gain on the 2-back test.
Other measures did not change: neck artery blood flow (769 vs 697 mL per minute), sleep efficiency (75.2% vs 76.2%), and blood amyloid and tau levels.
Should older adults take hot baths for brain health?
The study is a first careful look at repeated whole-body hot water immersion and thinking in older adults, and it reports a small, mixed signal rather than a clear benefit. A fair reading is that it supports running a proper trial with a comparison group, not a change of routine. It is not medical advice.
Safety deserves attention. Four participants fainted during the trial, two of them in the hot water, and the authors stress that a supervised laboratory does not reflect the risks of bathing at home.
On dementia, the blood markers linked to Alzheimer's disease did not change. The authors suggest 6 weeks may be too short to affect them, and note that neither exercise nor hot baths may be suitable ways to lower these markers.
What are the limits of the hot bath and cognition study?
Read before you quote it
The study has important limits:
- No control group. Without people who did the same tests but skipped the baths, gains from practice cannot be ruled out.
- Small and underpowered. Only 12 people completed it, and the secondary tests, where the gains appeared, had no power calculation.
- Unscreened participants. No one was screened for mild cognitive impairment, and education levels were not recorded.
- Safety outside the lab. Four participants fainted, and the results do not cover everyday settings.
- Funding. The study was part-funded by SPATEX and the British and Irish Spa and Hot Tub Association; the authors declare no conflict of interest.
The study does not show that hot baths prevent dementia or Alzheimer's disease, that they improve sleep or blood flow to the brain, or that long hot baths at home are safe for older adults.
- It does not show that hot baths prevent dementia or Alzheimer's disease; blood markers linked to them did not change.
- It does not show that hot baths improve sleep or blood flow to the brain, or explain how the test scores improved.
- It does not show that hot baths at home are safe for older adults.
- There was no control group, so the gains could partly reflect people getting better at the tests with practice.
- Only 12 people completed the study, and the secondary outcomes, where the gains appeared, had no power calculation.
- Participants were not screened for mild cognitive impairment, and no data on education were collected.
- Four participants fainted during the trial, two of them while in the hot water, and the authors say the lab results do not cover safety risks in everyday settings.
Takeaways
- saysAfter six weeks of hour-long hot baths, logical reasoning and a simple memory test improved, but the main memory test the study was built around did not.
- saysBrain oxygen dipped right after bathing and came back within three hours, so the gains weren't explained by more oxygen.
- saysWith only twelve people and no control group, getting better at the tests through practice can't be ruled out.
- explainsA learning effect is when scores rise simply because people have practised the tests, which is why a comparison group matters.
- interpretsA fair reading is that hot baths are worth a larger controlled trial, not a change of routine.
Ask the paper
In PaperSays you can ask this paper anything, by text or by saying “Hey Aiden”. Three questions listeners asked:
Do hot baths improve memory in older adults?
In this small study, a simple memory test improved but the main, harder memory test did not change after 6 weeks. Hear the full answer in the app →
Can hot baths lower the risk of Alzheimer's disease?
This study found no change in blood amyloid or tau after 6 weeks, so it cannot say that. Ask in the app →
Are long hot baths safe for older people?
Four participants fainted even in a supervised lab, and the results do not cover safety at home. Ask in the app →
Briefing reviewed by an editor before publication. The paper belongs to its authors; this page summarises it and links to the original. Paper licence: CC BY 4.0. Corrections: support@papersays.com.