Cold acclimation and brown fat: what 10 days changed
A small trial had adults spend hours in mild cold daily for 10 days. Brown-fat activity rose, but the exposure was far more than a typical cold plunge.
The short version
In this small study, 17 lean adults spent six hours a day for 10 days in a room kept at a mild 14-15°C, well short of shivering cold. Afterwards, PET scans showed more active brown fat and a bigger rise in heat production without shivering, and people said they felt warmer and more comfortable in the cold. No new brown fat appeared; existing brown fat simply became more active. There was no separate control group, each person was compared with their own earlier scan, and the daily exposure was far longer than a typical short cold shower or plunge.
Keep in mind
The exposure was six hours a day for 10 days, far more than a typical cold shower or plunge, and there was no separate control group.
What they found
After 10 days, brown-fat activity and non-shivering heat production both increased. There were no differences between men and women in brown fat before or after.
No new brown fat appeared in other fat tissue (no “browning” of white fat); the existing brown fat simply became more active. People also reported feeling warmer, more comfortable in the cold, and less inclined to shiver.
What this means for your practice
This shows that the body’s brown fat can adapt within days under sustained, hours-long mild-cold exposure. It does not tell us what a brief cold shower or plunge does to brown fat.
This does not establish a cold-exposure routine to follow. In KUUME, cold water is always your own choice, never a default.
Methods and limitations
What the researchers did
Seventeen lean adults (eight men, nine women) spent six hours a day, for 10 days in a row, in a room kept at a mild 14-15°C: cool enough to trigger the body’s non-shivering heat production, but not cold enough to cause shivering.
Researchers used PET/CT scans, the standard way to see brown-fat activity, before and after the 10 days, during a separate cold test.
There was no separate group that skipped the cold acclimation; each person’s scans were compared with their own scans from before the study.
How much can this tell us?
Comparing each person with their own earlier scan is a reasonable design for this kind of physiology study, but without a separate no-exposure control group, some of the change could reflect factors other than the cold itself.
Six hours a day for 10 consecutive days is far more cold exposure than most people get from a shower or a short plunge. This study cannot tell us whether brief, daily cold exposure would produce a similar change.
A rise in brown-fat activity is a physiological finding. It is not, by itself, a measured or lasting health benefit.
What makes it useful
- PET/CT imaging, a reliable way to see brown-fat activity
- Included both men and women, with no sex difference found
- Directly tested a “browning of white fat” claim and did not find it
What limits it
- Small (17 people) and no separate control group
- Six hours a day for 10 days is far more than a typical cold plunge
- A brown-fat change is not a measured health outcome
Where this study fits
Where this study fits
We score claims, not single studies. This one is part of the evidence for:
Cold plunges speed up your metabolism. Early signal
Very low certaintySize not reportedBody signals
Read the original
van der Lans AAJJ, Hoeks J, Brans B, et al. Cold acclimation recruits human brown fat and increases nonshivering thermogenesis. J Clin Invest. 2013;123(8):3395-3403.
DOI 10.1172/JCI68993 · PubMed 23867626