Researchers say a hot bath can help reduce inflammation and control blood sugar. But it’s not a substitute for exercise.

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A hot bath can help release anti-inflammatory chemicals in the body. Getty Images

You likely think of a relaxing bubble bath as the antidote to a stressful day.

It certainly can be that.

But new research suggests a long, hot bath may be as helpful to you as a gentle workout session, too.

British researchers report that hot-water immersion — that is, a long sit in a hot-water bath — may help reduce inflammation and control blood sugar levels in much the same way exercise does.

This is especially helpful for people who are unable to exercise or meet the weekly physical activity recommendations.

However, before you turn on your faucet and drop in a dissolving bath bomb, you should understand the limitations of these findings.

Role of inflammation in health

Inflammation after exercise, such as sore muscles and redness, is to be expected.

During brief physical stress, levels of inflammatory markers rise.

These markers signal the production of another inflammatory chemical called interleukin.

After this initial increase in inflammation, your body produces an extended release of anti-inflammatory chemicals. These substances combat the high levels of inflammation caused by the exercise.

This is a natural, normal process: Brief inflammation is followed by prolonged anti-inflammation.

However, when the anti-inflammatory process isn’t robust enough, your body may be left with chronic, low-grade inflammation.

This type of inflammation isn’t healthy. In fact, it may contribute to a number of health conditions, including obesity and diabetes.

Exercise can combat the inflammation, but not everyone is able to exercise. Or they may not be able to exercise at levels adequate enough to reap the anti-inflammatory rewards.

In recent years, research has shown that raising body temperatures can also influence the body’s inflammatory response.

What’s more, research suggests this same spike in body temperature may increase the production of nitric oxide. This substance in your blood can help improve blood flow and transport glucose throughout your body.

What’s been unclear, however, is if exercise alternatives, such as sitting in a hot tub of water, can produce the same low-grade inflammation and healthy anti-inflammation responses.

What the researchers found

For this test, researchers recruited 10 overweight and sedentary men.

The participants were divided into two groups. Both groups sat in an 80°F (27°C) room for 15 minutes.

Then, the first group of volunteers participated in an immersion bath in 102°F (39°C) water up to their necks for one hour.

The second group sat in a room at ambient temperature for the same amount of time.

In 15-minute intervals, researchers took measurements of each participant’s blood pressure, heart rate, and core temperature.

Blood samples were taken before the tests, immediately after the test, and in a follow-up session two hours after the test.

The researchers took blood samples from each of the men at these points in the study so they could examine the markers for inflammation, blood sugar, and insulin levels.

Three days after the first test, the participants returned and reversed roles.

The single hot-water immersion session did produce some positive effects.

Namely, it caused the levels of interleukin (the inflammatory chemical) to rise and increased the level of nitric oxide in the blood.

The rise in nitric oxide can cause blood vessels to relax, which can lower blood pressure. Nitric oxide is also thought to improve glucose intake by your body’s tissues.

For the final stage of the test, the participants returned to complete 10 hot-water immersion sessions in 14 days. The first five sessions were 45 minutes long. The final five were 60 minutes.

Blood samples taken after the two-week treatment period saw even greater results.

Fasting blood sugar and insulin levels were down, as were levels of low-grade inflammation.

These effects are similar to the impact exercise has on your body’s inflammation and glucose levels.

In other words, the hot-water immersion sessions were similarly beneficial as exercise in these men.

“Our study shows that even a single session induces a rise in markers that may positively affect health if repeated over two weeks,” Christof Leicht, PhD, MSc, one of the study’s authors and a lecturer in exercise physiology at Loughborough University in the United Kingdom, told Healthline. “It appears to be similar to exercise. One exercise session won’t do much to fitness or health, but repeated sessions show the desired effect.”

Exercise, hot water, and health

Heat and water therapies, such as saunas and hot baths, have been an area of scientific research for many years.

A 2016 study found that heat therapy can improve circulation and vascular function. This may reduce blood pressure and stiffening of the blood vessels.

Decades of research says that hot baths may improve sleep quality, too.

Your body’s core temperature rises while you’re sitting in a hot bath or sauna. Once you’re out of the hot environment, the slow temperature drop signals your body that it’s time for rest.

This may help you fall asleep and stay asleep.

Indeed, heat therapy’s perceived benefits makes it a target for people looking for alternative therapies.

Its relatively low cost and limited risks of possible side effects makes heat therapy a point of interest for many people looking for relief from a variety of health conditions.

This latest study, which was published in the Journal of Applied Physiology, outlines the impact heat therapy can have on inflammation markers and fasting blood sugar in your body.

Can baths replace gym time?

Leicht and his colleagues don’t go that far in their proposals.

“We do not suggest to replace exercise sessions with hot baths, as exercise has a multitude of proven positive effects, some of which are unlikely to be achieved when taking a bath at home,” Leicht said.

He cites an improvement in endurance and strength, social interactions, and the psychological benefits of exercising outside as reasons not to forego your treadmill time for a sit in a hot bath.

He does, however, suggest you supplement your workout routine with a hot bath for extra benefits.

“We would encourage people to top up their current exercise days with a hot bath or two,” Leicht told Healthline. “This especially applies to people who are restricted to adhere to recommended exercise guidelines.”

Nicky Kirk, DC, MSc, a chiropractic sports physician, also says a hot-water bath isn’t a good replacement for cardio and weight-bearing exercises.

Kirk says the benefits of exercise go beyond anti-inflammatory responses. They include decreased stroke risk, improved ability to think, decreased likelihood and severity of depression, lowered diabetes risk, and decreased risk of bone fracture.

A bath may not be this effective.

“The additional benefits of physical activity or exercise can include decreased risk of falling, decreased onset of dementia, improved joint health, and decreased risk of cancer,” Kirk told Healthline. “By immersing in water, we are losing the effects of weight-bearing on the joints and bones, the activity of the muscle pump which aids in venous return, strength and resilience of the heart as well as the musculoskeletal system.”

The men that participated in the study reported discomfort during the immersion sessions. This discomfort may be the result of the high temperature or the length of time they were required to sit in the hot water and remain immersed up to their neck.

These requirements may make adopting this type of alternative treatment difficult.

That’s why Leicht and his fellow researchers may look at research in the future that uses shorter immersion periods and lower water temperatures.

The bottom line

The results of this study indicate that hot-water baths may be beneficial for people who are sedentary or unable to exercise.

“If individuals are in a situation where their health is compromised and they are physically unable to participate in physical activity, hot-water immersion could be a useful modality to decrease some of the risk factors associated with obesity and inactivity,” Kirk said.

But for people who can exercise, this study isn’t permission to skip the gym and hit the hot tub.

Instead, you can use hot-water baths to supplement your workouts and possibly prolong your body’s natural inflammatory response.