Soaking in the bathtub does more than wash away stress. Hot baths have been associated with a host of health benefits from easing muscle tension and improving sleep to boosting mood and burning calories. The latest research shows hot baths reduce inflammatory markers, decreasing the risk of cardiovascular disease.
The small study, published in Physiological Reports, asked participants to soak in a hot bath up to their necks for 60 minutes and discovered hot water immersion increased adrenaline, stress hormones and glucose concentrations similar to a bout of exercise.
HOT BATHS VERSUS EXERCISE
“Fasting glucose gives us a rough indication of how well we can process sugar in foods [and] exercise is a good strategy … to lower fasting glucose levels; we were interested to find out whether hot water immersion would be capable of doing the same,” explains study co-author Christof Leicht, PhD, senior lecturer in exercise physiology at Loughborough University in the United Kingdom. “Elevated glucose concentrations following hot water immersion are in line with some exercise studies.”
The research builds on previous studies that found connections between long, hot bath and heart-health benefits. In sedentary, overweight adults, soaking in a hot bath for 10 one-hour sessions over two weeks led to reduced blood pressure and inflammation that can contribute to heart disease, according to 2018 research. A 2016 study showed an association between hot baths and improved circulation and vascular function.
A large Japanese study followed 873 adults between the ages of 60–76 years old and found those who soaked in a hot bath (with temperatures over 105ºF) for at least 12 minutes, five times per week, had a lower risk of atherosclerosis or hardening of the arteries. The researchers called it a “useful lifestyle intervention to preserve cardiovascular function.”
While the benefits are clear, the mechanism is hard to pin down.
Leicht suspects the increase in stress hormones during hot water immersion can trigger inflammatory pathways that activate the immune system and tax the cardiovascular system, providing stimulus similar to exercise. Additionally, he says, “The body will attempt to regulate its temperature: vessels will be forced to work and divert blood toward the skin, increasing blood flow — hence the healthy color [of our skin] when we step out of the bath — and vessel health may benefit as a result.”
TOO GOOD TO BE TRUE?
Soaking in a hot bath might seem like a zero-stress way to improve heart health but Leicht warns there is one significant downside: The water temperatures must be quite hot to achieve benefits. In most studies, temperatures were at least 102ºF and participants soaked for up to an hour.
“[It] was very comfortable at the beginning, but, toward the end, this was a struggle for most,” he admits.
In other words, it might be similar to the feeling you get toward the end of a heart-pumping one-hour workout — but that’s the point.
THE BOTTOM LINE
Hot baths are not a replacement for heart-healthy habits such as maintaining a healthy weight, limiting sugar and salt, exercising regularly and prioritizing sleep and Leicht doesn’t advise skipping the gym for quality time with your rubber duck. But, for those who cannot exercise due to disabilities or injuries, a hot bath can be a good strategy to maintain heart health (and reap the other rewards that come with soaking in the tub).
“[A hot bath] won’t improve your fitness the same way exercise does,” Leicht adds. “If you’d like give it a try, add a hot bath or two per week or go to the sauna. You may find that it relaxes you, improves your sleep and your mental health.”