Taking a nice, hot bath might be good for more than just your mental state. The passive heating from taking a bath—meaning not generated through exercise—can burn some calories, too.
In a study published in the journal Temperature, Loughborough University researchers found that hot baths can lower blood sugar, burn calories, and have an anti-inflammatory effect similar to what’s seen after exercise, as study co-author Steve Faulkner writes in The Conversation (as spotted by Town&Country).
The researchers had 14 men take a hot bath (104°F) for an hour, or do one hour of cycling, raising their core body temperatures around 1.8°F in both conditions. They measured how many calories the men burned during that hour and measured their blood sugar over the next 24 hours.
While cycling did burn more calories, as you might expect, bathing did have significant benefits. That hour-long soak burned about 140 calories—similar to what you’d see if you took a 30-minute walk. The men's blood sugar levels were about the same in both conditions, but just after eating, peak blood sugar values were about 10 percent lower for the bathers than for the cyclists. The bathers’ bodies showed an anti-inflammatory response similar to that associated with exercise, too, which can help protect against infection. All this indicates that raising your body temperature is good for you, whether you do it by running or by taking a long, hot soak.
The study only examined 14 men, making its findings far from definitive. However, people have sworn by the restorative nature of sauna-ing for centuries, and there has been some other modern science to back the idea up. One 20-year study of 2000 Finnish men found that those who spent time in a sauna every day were less likely to die from heart problems than those who only visited a sauna once a week. (Despite some concern over people with heart problems using saunas, scientific reviews have found the practice to be generally safe.) Previous studies have also found that passive heating from saunas and baths raises levels of nitric oxide, which reduces blood pressure, and can reduce dependence on insulin for type 2 diabetics.
So go ahead, treat yourself to that bath. It’s for your health. Just make sure it's nice and hot.