The Problem: People With Large Amounts of Body Fat are More Likely to Get Chronic Diseases

You probably remember the last time you were ill: a sore throat, a bad cough, inability to eat as much as normal, and maybe you could not even go to school. Your symptoms, however, probably ended after a few days, leaving you feeling completely fine. You can thank your immune system for your recovery, since it fired up quickly and got rid of the things in your body that made you ill. With chronic diseases, on the other hand, people are ill for a much longer time–sometimes even their whole lives.

One example of a chronic disease that many people in countries, such as the United States and the United Kingdom suffer from is called type 2 diabetes mellitus, which we will just call diabetes 2. Diabetes 2 is a condition in which people have difficulty processing the sugar in the foods they eat. As a result, the concentration of sugar in the blood can get out of control and cause all sorts of damage. The reasons that people get this condition are not completely clear, but one of the causes may be something called chronic inflammation. This is the long-term overactivation of the immune system. In contrast to the immune system acting like a brief and intense fire to help get rid of a virus in your body when you have a cold, chronic inflammation can be compared to a small campfire that somebody forgot to put out and that keeps on glowing. Chronic inflammation can impair the way organs and tissue process the sugar in foods. Because fat cells in the body contain a lot of over-active immune cells that help to keep the immune campfire glowing, people with high amounts of body fat have a greater chance of getting chronic inflammation. Scientists have suggested that this may be one of the reasons people with more body fat are also more likely to get diabetes 2 [1].

The Good News: Exercise May Help to Reduce Chronic Inflammation

Luckily, there are ways to put out the immune campfire and reduce chronic inflammation. Although there are pills that may help, exercise is a much cheaper and more fun way of keeping the immune system in check. Indeed, people who exercise have better-balanced, and thus less over-active, immune systems compared with people who never exercise. In addition, studies in which participants complete an exercise program have found that these participants have better-balanced immune systems after the program [2]. Thus, exercise may help to reduce chronic inflammation and therefore also reduce the risk for diseases like diabetes 2.

But how does exercise do this? It is still uncertain, since there is still a lot we do not know about the human body, but part of the healthy effect of exercise may come from a substances that are produced by the body each time you exercise. When you exercise, your body does not only kick a ball or run around the track–your liver, kidneys, muscles, and brain also produce a lot of these healthy substances. There is one important thing to know about these substances: they might reduce the over-activity of the immune system [3], somewhat like fire-fighters that put out the glowing campfires in people with chronic inflammation. Although we measured a few different sorts of fire-fighting substances, the one we focus on here is called interleukin-6 (IL-6).

Another Problem: What if People are not Able to Exercise?

So, maybe it sounds easy: we just tell everybody to exercise and the fire-fighters in the blood make sure that people do not get chronic inflammation. But what if your body does not allow you to exercise? Elderly people, for example, sometimes do not have the strength to ride a bicycle or to go for a walk. In other people, disabilities can prevent them from doing exercise. For these people, it is difficult to increase the numbers of fire-fighters by exercising. So, to keep these people healthy, we need an alternative to exercise that stimulates production of the healthy fire-fighting substances.

Researchers from around the world are working on different alternatives for people unable to exercise. For example, there are machines that can use electrical stimulation to help people with paralyzed legs to cycle. Other researchers have found that your body temperature increases when you exercise. Even more interesting is that, when you exercise in the heat (temperature between ~25 and 35°C), your body produces a larger amount of fire-fighters than when you exercise in colder weather (below ~25°C) [4]. So, getting warm may be important for your body to produce these fire-fighters. If getting warm is indeed important, would that mean that warming people up in the absence of exercise could improve their health? Could we place people in hot water to increase the amount of fire-fighting substance and reduce their risk for diabetes 2?

A Potential Alternative: Testing the Effects of Hot Baths on Health

To test the idea that hot baths might substitute for exercise, we asked 10 male adults with a bit too much body fat to take part in the study. An overview of this study can be seen in Figure 1. To investigate the short-term effects of hot baths, the participants sat in water of 39°C for 1 h. Before and after that hour, we took blood samples to measure the amount of the fire-fighting substance.

After the short-term part of the study, participants participated in the long-term part. For this, they took 10 hot baths within 2 weeks. To study whether these 10 hot baths improved the health of our participants, we took blood samples and measured their blood pressure at the start and at the end of the 2 weeks. We measured the amount of sugar in the blood sample. A reduction in blood sugar is generally believed to reduce the risk of getting diabetes 2, and a reduction in blood pressure reduces the risk of getting another chronic disease called cardiovascular disease.

Study Results: Hot Baths May Improve Health!

The most important findings of the study are shown in Figure 2. Even one hot bath increased the concentration of the fire-fighting substance IL-6 in the blood. Since we would like to improve people's health for longer than 1 day, the long-term study results are even more important. In the long-term study, we found that, after 10 hot baths within 2 weeks, participants' blood sugar concentrations were lower than they were at the start of the study. Their blood pressure readings were also reduced at the end of the 2-weeks study period.

The Interpretation: What do These Results Mean?

The short-term increase in the blood concentration of the fire-fighting substance IL-6, the reduction in blood sugar concentration, and the lowering of blood pressure after the long-term part of the study are promising findings for the use of hot baths as an alternative to exercise. It is, however, important to realize that we still need to know a little bit more before we can advise hot baths for people who are unable to exercise. For example, the long-term part of the study consisted of a lot of hot baths in only 2 weeks' time. Most people are probably too busy with other things, like work, to take this many baths. In the future, we would like to test whether taking fewer baths per week, but over a longer duration, like several months, also improves health. Also, we have only investigated the effects of hot baths in men, and it would be interesting to find out whether baths can also improve health in women.

Another thing to consider is that a bath of 39°C for 1 h makes you feel really, really, warm. Although a hot bath sounds relaxing, feeling that warm can be unpleasant. As a result, people may stop taking hot baths after only 1 week, if they do not like them. To make sure that people keep taking hot baths after their first week, we should come up with ways that these baths can become more pleasant and enjoyable.

The Conclusion: Should We All Take Hot Baths?

The results of this study are encouraging for the use of hot baths as an alternative for people that cannot exercise. However, before we advise hot baths in such situations, there is still a lot to find out. Maybe one day we will be able to say to these people, “A hot bath a day keeps the doctor away!”

Glossary

Type 2 Diabetes Mellitus: ↑ Type 2 diabetes mellitus is a condition in which people have difficulty processing the sugar in the foods they eat. When not treated, this can damage for example your blood vessels.

Chronic Inflammation: ↑ This is the long-term overactivation of the immune system and can increase the risk for chronic diseases.

Cardiovascular Disease: ↑ A collection of diseases affecting the heart and blood vessels. In the most severe cases it can prevent blood going to the brain or even cause the heart to stop beating.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.