Is it time to start recommending regular sauna bathing to improve heart health?
While a post-workout sauna can compound the benefits of exercise, the hormetic effects of heat therapy alone can produce significant gains for microvascular and endothelial function, no workout required.
“There’s enough evidence to say that regular sauna use improves cardiovascular health,” Matthew S. Ganio, PhD, a professor of exercise science at the University of Arkansas in Fayetteville, who studies thermoregulatory responses and cardiovascular health, said.
“The more they used it, the greater the reduction in cardiovascular events like heart attack. But you don’t need to be in there more than 20-30 minutes. That’s where it seemed to have the best effect,” Dr. Ganio said, adding that studies have shown a dose-response.
A prospective cohort study published in 2015 in JAMA Internal Medicine included 20 years of data on more than 2,300 Finnish men who regularly sauna bathed. The researchers found that among participants who sat in saunas more frequently, rates of death from heart disease and stroke were lower than among those who did so less often.
Cutaneous vasodilation
The body experiences several physiologic changes when exposed to heat therapy of any kind, including sauna, hot water submerging, shortwave diathermy, and heat wrapping. Many of these changes involve elements of the cardiovascular system, said Earric Lee, PhD, an exercise physiologist and postdoctoral researcher at the University of Jyväskylä in Finland, who has studied the effects of sauna on cardiovascular health.
The mechanisms by which heat therapy improves cardiovascular fitness have not been determined, as few studies of sauna bathing have been conducted to this degree. One driver appears to be cutaneous vasodilation. To cool the body when exposed to extreme external heat, cutaneous vessels dilate and push blood to the skin, which lowers body temperature, increases heart rate, and delivers oxygen to muscles in the limbs in a way similar to aerobic exercise.
Sauna bathing has similar effects on heart rate and cardiac output. Studies have shown it can improve the circulation of blood through the body, as well as vascular endothelial function, which is closely tied to vascular tone.
“Increased cardiac output is one of the physiologic reasons sauna is good for heart health,” Dr. Ganio said.
During a sauna session, cardiac output can increase by as much as 70% in relation to elevated heart rate. And while heart rate and cardiac output rise, stroke volume remains stable. As stroke volume increases, the effort that muscle must exert increases. When heart rate rises, stroke volume often falls, which subjects the heart to less of a workout and reduces the amount of oxygen and blood circulating throughout the body.
Heat therapy also temporarily increases blood pressure, but in a way similar to exercise, which supports better long-term heart health, said Christopher Minson, PhD, the Kenneth M. and Kenda H. Singer Endowed Professor of Human Physiology at the University of Oregon in Eugene.
A small study of 19 healthy adults that was published in Complementary Therapies in Medicine in 2019 found that blood pressure and heart rate rose during a 25-minute sauna session as they might during moderate exercise, equivalent to an exercise load of about 60-100 watts. These parameters then steadily decreased for 30 minutes after the sauna. An earlier study found that in the long term, blood pressure was lower after a sauna than before a sauna.