Heat, cold, and circulation
When you get hot, your body pushes blood toward your skin to cool off. Researchers are testing whether doing that on purpose trains your blood vessels.
The short version
- Heat makes blood vessels widen and heart rate rise, a bit like light exercise.
- Finnish men who used a sauna 4 to 7 times a week had far fewer sudden cardiac deaths than once-a-week users.
- Cold water studies are small. Cold shock can be risky for people with heart disease.
What heat does to blood flow
When your core temperature rises, vessels near the skin open wide, heart rate climbs, and blood flow increases across the body. That faster flow triggers the vessel lining to make nitric oxide, the same signal exercise produces.
The Finnish sauna study
Researchers followed 2,315 middle-aged Finnish men for about 20 years. Compared with once a week, men who used a sauna 4 to 7 times a week had a 63% lower risk of sudden cardiac death. Sessions longer than 19 minutes were also linked to lower risk. This is observational, so it shows a link. Men who sauna often may differ in other ways.
A hot tub trial
A small University of Oregon trial put 10 sedentary young adults in 40.5°C (105°F) water for an hour, 4 to 5 times a week, for 8 weeks. Their flow-mediated dilation (a measure of how well arteries widen) nearly doubled, from 5.6% to 10.9%, and their arteries got less stiff. A comparison group in cooler water saw no change.
Cold: less evidence, more caution
Cold water makes surface vessels tighten sharply and blood pressure jump. Studies on regular cold plunges and circulation are small and mixed so far. The sudden shock of cold water can be dangerous for people with heart disease.
Who should check first
If you have heart disease, low blood pressure, are pregnant, or take medicines that affect blood pressure, ask your doctor before using a sauna or hot tub regularly. Skip alcohol before and stay hydrated.
Sources
Educational information, not medical advice. Read our medical disclaimer.