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Are hot tubs or saunas better? Sunday Morning
The study, published in the American Journal of Physiology , compared three forms of passive heat therapy: hot water immersion, traditional dry saunas and far infrared saunas.
Twenty healthy adults took part, undergoing sessions in 40.5C hot water, an 80C traditional sauna, and a far infrared sauna heated between 45C and 65C. Researchers monitored changes in body temperature, heart rate, blood pressure and immune responses.
Hot water immersion produced the strongest physiological response, Atencio said.
“Hot tubs may be more useful for eliciting beneficial adaptations. We’re suggesting that hot tubs may be the best, most robust modality for health.”
Researchers found hot water immersion was the only heating method to trigger a measurable immune response. Participants also recorded the biggest increases in core body temperature and cardiac output.
Atencio said the benefits came from how the body responds to heat.
Why baths beat saunas
Atencio said water transferred heat through the body much more effectively than hot air.
“You can’t sweat as effectively. So, you can’t actually release that heat as effectively as you would if your skin was exposed to air,” she said.
“The conduction of water is, I think, 24 times that of air.”
This meant those in the hot water sessions during the study heated up faster and stayed hotter longer than those in either sauna group.
By comparison, the infrared sauna produced “very minimal changes in core temperature”, despite being marketed as a deeper form of heat therapy.
Researchers cautioned passive heat therapy was not risk-free.
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‘Exercise in a bath’
Researchers say one of the most interesting findings is that passive heat therapy may mimic some of the body’s responses to exercise.
“And what’s good about that is an inflammatory response is met with an anti-inflammatory response.”
“A lot of chronic diseases are associated with chronic inflammation.”
How hot for how long?
A study led by researchers at the University of Oregon found hot water immersion triggered stronger cardiovascular and immune responses than both traditional and infrared saunas, suggesting a simple soak offers surprisingly powerful health benefits.
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The study used water heated to 40.5C for 45 minutes – conditions Atencio described as “quite stressful and quite long”.
But she said shorter sessions could still help.
“I think if you can get in the hot tub for 30 minutes … when you’re feeling like you’re sweating, really you feel like your heart rate’s increasing, your body’s trying to work against a stressor.”
For people without hot tubs, she said ordinary baths could still provide benefits, although they cooled more quickly.
“Even if it’s 10 to 15 minutes every day, there can still be some… beneficial adaptations that occur.”
Not for everyone
Researchers cautioned that passive heat therapy was not risk-free.
Atencio said people with serious cardiovascular conditions should speak to a doctor before trying prolonged hot water immersion.
“If you start to feel lightheaded or woozy of any sort, definitely get out of the heat,” she said. “Definitely make sure you’re drinking water while you’re there.”
She said the findings were promising, but the science around heat therapy was still developing.
Still, for New Zealanders reaching for the hot tap this winter, the research offers another reason to stay in the bath a little longer.
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