Seven warm immersions and two brain-related proteins

Some of the most interesting heat research right now is not about saunas at all. It is about warm water.

The study

Researchers at the University of Ottawa published this work in Experimental Physiology in 2026. It followed twelve habitually active men with a median age of 68.

For seven consecutive days, each man sat in water at about 40 °C for roughly 90 minutes. For the final hour, the team held core temperature near 38.5 °C.

What they measured

Blood levels of three proteins that researchers associate with healthy ageing:

• Irisin, released by muscle, often during exercise
• BDNF, brain-derived neurotrophic factor, which supports the growth and survival of nerve cells
• Klotho, a protein linked with ageing in animal research

What they found

After the week of warm water, resting irisin and BDNF were higher. Klotho did not change.

The authors suggest passive heat could be a way to support cellular resilience in people for whom exercise is limited.

What it does not show

Twelve men, one week, one group. There was no comparison group, and the study measured proteins in blood, not memory or thinking.

So this is not evidence that warm baths improve brain function. It is an early, interesting signal about what heat does in older bodies.

It is also a laboratory protocol. Holding core temperature at 38.5 °C for an hour was done with monitoring. Please do not try to replicate it at home.

Why we are paying attention

The same Ottawa group has shown that a week of this kind of warm water immersion helped older men shed heat more effectively during exercise in hot conditions. We will write about that before summer.

Our N-02 is an ice bath that also heats, up to 40 °C, the same water temperature used here. We think of the warm setting as a gentle, everyday option: shorter soaks, well hydrated, and out if you feel light-headed.

Free: The Norge Longevity Guide. Heat, cold and light after 50, with the evidence and the safety rules in one place. Get the guide.

Sources

1. Garrett et al., Seven days of warm-water immersion enhances resting irisin and BDNF, but not klotho, in older men, Experimental Physiology, 2026
2. Janetos et al., Short-Term Warm Water Immersion for Improving Whole-Body Heat Loss in Older Men, 2025

This article is general information, not medical advice. If you have a heart condition, low blood pressure or are pregnant, speak with your GP before using heat or cold.