Hot tubs may offer greater health benefits than saunas

Hot tubs and saunas can both soothe aching muscles and provide welcome warmth, but hot tubs might offer greater health benefits.

That's the takeaway from a new study done by researchers in the Bowerman Sports Science Center at the University of Oregon, which compared the physiological effects of soaking in a hot tub to sitting in a traditional dry heat sauna or a more modern far-infrared sauna.

By raising core body temperatures, soaking in hot water can help lower blood pressure, stimulate the immune system and, over time, improve the body's response to heat stress. Moreover, those effects can last beyond the minutes spent directly in heat treatment.

"We compared the most commonly utilized modalities of passive heating as they're used in everyday life and studied in scientific research," said study lead author Jessica Atencio, a doctoral student in the lab of Christopher Minson. "No studies have compared the acute responses between the three."

The results were published in June in the American Journal of Physiology.

Under the guidance of Minson, the Kenneth M. and Kenda H. Singer Endowed Professor of Human Physiology and director of the Bowerman Center, researchers monitored body temperature, blood pressure, heart rate, cardiac output (the amount of blood the heart pumps per minute) and immune cell populations and blood biomarkers of inflammation. Data were collected before, during and after subjects soaked in a hot tub and sat in traditional dry heat and far-infrared saunas.

The study looked at 10 men and 10 women who exercised regularly and ranged in age from 20 to 28 years old. The goal was to isolate the physiological responses to each heating method in a young, healthy population.

We saw that hot water immersion was the most impactful in increasing core body temperature, which is the main stimulus for these subsequent responses. Increasing body temperature causes an increase in blood flow, and just the force of blood moving across your vessels is beneficial for your vascular health."

Jessica Atencio, study lead author 

While the research team took blood samples from subjects after each kind of heat therapy, only hot-water immersion produced an inflammatory response as measured by the levels of inflammatory cytokines, a kind of immune signaling molecule, and immune cell populations.

Atencio and her team were not surprised by those results.

"Hot water immersion gives you the most robust changes in core temperature because you can't effectively dissipate heat as you can if you have contact with the air and you're sweating to cool the body," she said. "When you're submerged in water, the sweat mechanisms aren't efficient."

Minson has studied heat therapies for more than two decades. He has focused on how heat interacts with factors such as age, exercise and illness in men and women.

"There's no doubt in my mind that if people are willing to do some heat therapy, it's going to align with improved health, as long as it's done in moderation," Minson said. "If you repeat these stresses over time, our lab and many others have shown that they are consistent with improved health."

Regular exercise can provide benefits similar to and even better in some respects than those from heat therapy, he added, but individuals who are unable or unwilling to exercise may find that heat therapy provides an attractive option.

"It can be a very peaceful, sometimes religious, sometimes cultural and sometimes social experience," Minson said. "And I think those aspects contribute to the health benefits and are critically important."

"We want people to be smart and safe about it," he added. "We need to make sure that they are cleared by their physicians or others for heat therapy or for exercise, whether it's mild to moderate walking or jogging or strength training. Then they'll be fine to do heat therapy."

As a runner herself, Atencio knows people who like to combine heat therapy with exercise.

"We always say that exercise is the primary nonpharmacological treatment that people should be doing to promote health, but some people can't or just won't exercise," she said. "Heat therapy is good supplementation."