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Claim that hot baths can substitute for exercise lacks evidence

Can't exercise? A hot bath may help improve inflammation, metabolism, study suggests

Our Review Summary

Take a look at the headline and subheading of this news release, because the former is very misleading, and the latter comes closer to the truth:

Headline: ‘Can’t exercise? A hot bath may help improve inflammation, metabolism, study suggest’

Sub-head: ‘Hot-water immersion improved inflammatory markers and blood sugar in overweight men’

The subheading is a fairly good summary of the study.

But the “Can’t exercise? …” headline promises much more than this small study can support. The research question?  How does hot water immersion —  that is, ten 1-hour soaks at 102ºF over two weeks  — affect metabolic and inflammatory biomarkers in the blood of 10 overweight and sedentary men. The answer? Some mild, transient changes were noted that could theoretically be beneficial.


Why This Matters

Just because exercise has been shown to transiently increase inflammatory markers and decrease blood sugar, and hot water immersion does the same thing, doesn’t mean that the latter might substitute for the former.

Furthermore, the research into the relationship between inflammation and sugar/insulin levels is mostly in rodents, and extrapolating these benefits to humans is unrealistic.

Yes, exercise can temporarily trigger an anti-inflammatory response at the molecular level, as well as decrease sugar/insulin levels. This study suggests repeated, lengthy hot water immersion can do the same thing in 10 overweight men. But that hardly means the two interventions are comparable in any way, or that these blood changes have any meaningful or sustainable clinical benefits.


Does the news release adequately discuss the costs of the intervention?

Not Applicable

Cost isn’t really applicable here;  but it’s important to point out that probably the best way to access a hot water source that consistently stays around 102ºF would be a hot tub, and that would involve cost for most people.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

This is a major weakness of the release. We’re told that hot water immersion (60 minutes, daily at 102ºF) elevated levels of:

  • Inflammatory marker, IL-6, which in turn “activates the release of anti-inflammatory substances to combat unhealthily high levels of inflammation.”
  • Nitric oxide … “a substance that aids in blood flow and helps carry glucose throughout the body.”

This is nebulous, if not unhelpful language, that suggests (unquantified) benefits that are hard to make sense of. Furthermore, it’s mentioned 10 soaks over 14 days led to:

“a reduction of fasting blood sugar and insulin levels as well as improved low-grade inflammation at rest.”

Both diabetics and non-diabetics alike would appropriately ask, “really? By how much? For how long?” But that information is not provided.

Nor is any context provided for readers wondering how changes in metabolic and inflammatory biomarkers translate into noticeable or measurable clinical effects that matter to them.

Does the news release adequately explain/quantify the harms of the intervention?

Not Satisfactory

Harms are not mentioned.

Anyone who owns a hot tub, or uses a public bath, is likely familiar with warnings regarding who might want to consult their physician before using one.

Prolonged exposure to hot water can lead to increased heart rate, decreased blood pressure, and dehydration … all of which may be ill-advised for some heart patients and pregnant women.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

The study was extremely small (10 volunteers), short (2 weeks), and because the subjects were only men who were obese or inactive, probably not applicable to the general public. This wasn’t mentioned.

Nor is it mentioned that most of the existing research on the relationship between inflammatory biomarkers and glucose/insulin levels — which is strongly touted in this release — is based on animal models.

That should have been clarified since the headline of this news release suggests human benefits. That’s speculative at best, and at worst misleading.

Does the news release commit disease-mongering?

Not Satisfactory

No overt disease mongering but there’s an inappropriate and baseless implication that those who are unable to exercise — or are obese or sedentary — have problems with blood sugar or ‘inflammation’; and that those two problems are likely related. That’s just not the case and misleading enough to warrant an unsatisfactory rating here.

Does the news release identify funding sources & disclose conflicts of interest?

Not Satisfactory

Funding is not mentioned.

A review of the published article doesn’t suggest conflicts of interest among the researchers.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

Alternatives to what?

If the gist of this release is that overweight and sedentary men can’t exercise (and hot water immersion might be a good replacement), then this news release never should have been published because the premise and conclusion are both erroneous.

But if the gist is that there ARE people — such as those who are frail, disabled, or paralyzed — who might benefit from an intervention that offers the benefits from exercise they can’t do, then this news release is misleading.

Because all this study shows is that hot water immersion changes some metabolic and inflammatory biomarkers. Yes, exercise can do that too, but the real benefits and sustainability of these blood changes remain unproven.

Does the news release establish the true novelty of the approach?

Not Satisfactory

The exact results of this small human study are new but many researchers have been working on theories and rodent studies regarding heat therapy and chronic inflammatory diseases. Much of this was summarized by Ely et al in 2017 in the journal Temperature, “Meta-inflammation and cardiometabolic disease in obesity: Can heat therapy help?

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?

Not Satisfactory

The headline is both unjustified and inappropriate. First of all, most people don’t bathe for one-hour straight in a bath locked in at 102º F.

Second, a study of 10 men over 2 weeks can’t draw any conclusions regarding inflammation and metabolism.

Finally,  what’s inappropriate here is that there are plenty of people physically incapable of conventional exercise; why lead with the enticement of “Can’t exercise?” when the referenced study offers no proof that the hot water immersion offers the benefits of exercise?

Total Score: 0 of 8 Satisfactory


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