Can a Hot Bath Improve Your Cardiovascular Health?

Exercise is one of the best things you can do for cardiovascular health. That isn't particularly controversial.

But there's another intervention getting considerably more attention lately: heat.

Saunas, hot baths, and other forms of heat therapy have been associated with improvements in cardiovascular function, and some of the physiological responses to heat look surprisingly similar to what happens during aerobic exercise. Blood vessels dilate, blood flow to the skin increases, the heart works harder, and the increased blood flow creates shear stress along the walls of your arteries.

That raises an interesting question.

Can repeatedly sitting in hot water actually produce some of the same vascular adaptations as exercise?

A new 2026 randomized controlled trial published in Experimental Physiology tested that question directly. Researchers compared 12 weeks of aerobic exercise, hot water immersion, or no intervention in inactive older adults with overweight or obesity.

The answer was more interesting than I expected.

Hot water immersion improved one important measure of blood vessel function, and the improvement was not statistically different from exercise.

But before anyone cancels their gym membership and orders a hot tub, there's quite a bit more to the story.

TLDR: Hot Water Improved Vascular Function, But It Didn't Replace Exercise

This was a small study, so I wouldn't use it to claim that hot baths are cardiovascular exercise. What it does show is that repeated heat exposure can create meaningful vascular adaptations, even without traditional exercise.

• The study included 31 inactive adults averaging 58 years old with an average BMI of 30.1.
• Participants completed either aerobic exercise, hot water immersion, or remained inactive for 12 weeks.
• Both exercise and hot water immersion were performed three times per week.
• Hot water immersion involved sitting in 40°C (104°F) water for up to 40 minutes.
• Exercise consisted of progressively harder stationary cycling for up to 40 minutes per session.
• Brachial artery flow mediated dilation increased by approximately 1.0 percentage point with exercise and 0.5 percentage point with hot water immersion.
• Both improvements were statistically significant compared with baseline, and the changes between exercise and hot water immersion were not significantly different.
• Exercise produced a broader effect, significantly improving femoral artery endothelial function, while hot water immersion did not.
• Neither intervention significantly improved resting blood pressure or arterial stiffness.
• The practical takeaway is that heat therapy may provide some cardiovascular benefits, particularly for people who have difficulty exercising, but it should not be considered a replacement for exercise.

Why Would Sitting in Hot Water Affect Your Cardiovascular System?

At first glance, sitting in a hot tub and riding a stationary bike don't seem particularly similar.

Your cardiovascular system sees things a little differently.

When body temperature rises, your body needs to get rid of that heat. Blood vessels near the skin dilate and blood flow is redirected toward the body's surface. That increased blood flow changes the forces acting against the inside walls of your arteries.

One of those forces is called shear stress.

Shear stress is essentially the frictional force created as blood flows along the inner lining of a blood vessel. Repeated increases in arterial blood flow and shear stress are believed to be an important signal that encourages blood vessels to adapt and become better at dilating.

Exercise creates this stimulus.

Interestingly, heat exposure can create it too.

The researchers point out that arterial blood flow and shear stress during heat exposure can resemble some of the changes observed during aerobic exercise. Hot water immersion also has the added effect of hydrostatic pressure from the water, which can increase venous return and cardiac filling.

So you're obviously not exercising while sitting in a hot tub.

But your cardiovascular system isn't exactly sitting around doing nothing either.

How the Study Worked

Researchers recruited inactive men and postmenopausal women who were generally between 45 and 70 years old and had overweight or obesity, often accompanied by at least one weight related health condition.

Of the 34 people randomized, 31 completed the study.

Their average age was 58 years, average BMI was 30.1 kg/m², and 22 of the 31 participants were women. Some participants also had conditions including high cholesterol and hypertension.

Participants were randomly assigned to one of three groups.

Eleven completed aerobic exercise.

Eleven completed hot water immersion.

Nine served as inactive controls.

The intervention lasted 12 weeks, with the exercise and hot water groups completing their respective protocols three times per week.

The diagram on page 4 of the paper makes the comparison particularly easy to visualize. Both intervention groups followed almost identical schedules, with three 40 minute sessions each week, while the control group continued its normal activities and diet.

That makes this an especially interesting head to head comparison.

What Did the Exercise Group Do?

The exercise group used stationary bikes.

During the first two weeks, participants exercised for 30 minutes at approximately 55 to 65% of maximum heart rate.

The program then progressively became harder.

During weeks three through six, intensity increased to 65 to 70% of maximum heart rate. During weeks seven through ten, it increased to 70 to 75%, and during the final two weeks participants reached approximately 75 to 85% of maximum heart rate.

Sessions eventually lasted 40 minutes, three times per week.

This wasn't an extreme exercise program.

It was basically a progressive moderate intensity aerobic training program that most people would recognize as a pretty reasonable cardiovascular workout.

What Did the Hot Water Group Do?

The hot water protocol was even simpler.

Participants came to the laboratory three times per week for 12 weeks and sat in water heated to 40°C, or 104°F.

During the first two weeks, sessions lasted 30 minutes. From weeks three through twelve, they increased to 40 minutes.

Participants were seated with the water reaching approximately the level of the xiphoid process, around the lower portion of the sternum, and their arms were submerged as well. Sessions were supervised by an exercise physiologist.

So we're talking about roughly:

40 minutes.

104°F water.

Three times per week.

Twelve weeks.

Not exactly a brutal training program.

Yet something changed.

Hot Water Improved Endothelial Function

The most interesting outcome involved flow mediated dilation, commonly abbreviated FMD.

FMD is a noninvasive method researchers use to assess endothelial function. The endothelium is the thin layer of cells lining the inside of your blood vessels, and its ability to respond appropriately to changes in blood flow is an important component of vascular health.

In this study, researchers measured FMD in both the brachial artery in the arm and femoral artery in the leg.

After 12 weeks, brachial artery FMD significantly improved in both intervention groups.

Exercise increased brachial FMD by approximately 1.0 percentage point.

Hot water immersion increased it by approximately 0.5 percentage point.

The control group essentially didn't change, decreasing by approximately 0.1 percentage point.

Here's the particularly interesting part.

The improvement produced by hot water immersion was not statistically different from the improvement produced by exercise.

That's a legitimate finding.

It's also one that needs to be interpreted carefully.

Does That Mean Hot Baths Are As Good As Exercise?

No.

And this is exactly where I can see this study getting turned into a ridiculous social media headline.

"Scientists Discover Hot Tubs Are Just As Good As Exercise."

That's not what the study showed.

Researchers measured several aspects of vascular function, and the results weren't identical between the two interventions.

Exercise significantly improved brachial artery FMD from baseline.

Hot water immersion significantly improved brachial artery FMD from baseline.

But when researchers looked at the femoral artery in the leg, only exercise produced a statistically significant improvement from baseline.

Exercise increased femoral FMD by approximately 1.5 percentage points.

Hot water immersion increased it by approximately 0.5 percentage point, but that change was not statistically significant.

The researchers interpreted this as evidence that exercise may create broader systemic vascular adaptations than hot water immersion.

That's a pretty important distinction.

Hot water produced a measurable vascular benefit.

Exercise produced a broader one.

Why Exercise May Have Done More

The researchers offer an interesting explanation for why exercise appeared to produce greater adaptation in the lower body.

Exercise doesn't provide just one physiological stimulus.

During aerobic exercise, muscles contract repeatedly, oxygen demand rises, cardiac output increases, blood flow changes throughout the body, and numerous signaling molecules are released.

The researchers note that exercise may stimulate circulating factors including heat shock proteins, vascular endothelial growth factor, and nitric oxide, all of which can contribute to vascular adaptation.

There's also an important difference in how the interventions progressed.

The exercise program became progressively more difficult. Participants eventually moved from 55 to 65% of maximum heart rate up to 75 to 85% of maximum heart rate.

The hot water remained at 40°C throughout the intervention. Only session duration increased.

The authors suggest that the lower limb arteries may require a stronger or progressively increasing stimulus to continue adapting.

In other words, your cardiovascular system may respond to progressive overload just like many other physiological systems do.

You can't exactly add another plate to the hot tub.

The Nitric Oxide Connection Is Particularly Interesting

There's another reason I'm interested in this research.

Nitric oxide plays an important role in how blood vessels dilate.

The endothelium releases nitric oxide in response to increased blood flow and shear stress. Nitric oxide then helps relax vascular smooth muscle, allowing the blood vessel to expand and accommodate greater blood flow.

The researchers discuss previous experiments in which heat or exercise increased shear stress in arteries. When researchers artificially prevented that increase in shear stress in one limb, the vascular adaptation was eliminated.

That provides pretty compelling evidence that the increased blood flow itself is an important part of the adaptation.

This is also why nitric oxide gets so much attention in exercise physiology.

The nitrate to nitrite to nitric oxide pathway is one reason dietary nitrate has become interesting for endurance performance and cardiovascular health. But this study highlights another side of the equation.

You can also stimulate vascular nitric oxide related signaling through behavior, including exercise and repeated heat exposure.

That's considerably more interesting to me than simply trying to solve everything with another supplement.

Hot Water Didn't Lower Blood Pressure

This result surprised me a little because heat therapy is frequently promoted as a way to lower blood pressure.

That didn't happen here.

Researchers measured systolic blood pressure, diastolic blood pressure, and mean arterial pressure before and after the intervention.

There were no significant intervention effects showing that either exercise or hot water immersion reduced resting blood pressure compared with the other groups.

That's worth highlighting because it demonstrates why we need to be careful about turning a plausible mechanism into a guaranteed outcome.

Heat causes blood vessels to dilate acutely.

That doesn't automatically mean twelve weeks of hot baths will meaningfully lower resting blood pressure.

In this study, it didn't.

Arterial Stiffness Didn't Improve Either

Researchers also measured pulse wave velocity, or PWV, which is commonly used as a measure of arterial stiffness.

Again, there was no significant improvement with either exercise or hot water immersion.

The authors discuss several possible reasons.

Previous research suggests arterial stiffness may be more likely to improve in people who begin with relatively stiff arteries or after higher intensity exercise interventions. The participants in this study may simply not have had enough baseline arterial stiffness for a large change to occur.

This is another reason the headline shouldn't be:

"Hot baths improve every marker of cardiovascular health."

They didn't.

The strongest finding was specifically related to endothelial function.

Why Endothelial Function Matters

Your arteries aren't just passive pipes carrying blood around your body.

The endothelium lining those arteries actively regulates vascular tone, blood flow, inflammation, clotting, and other aspects of cardiovascular function.

Healthy arteries need to be able to dilate when tissues require additional blood flow.

Flow mediated dilation gives researchers a way to evaluate that ability.

The authors concluded that the increases in FMD observed in the study were consistent with improvements in endothelium dependent vasodilation, rather than changes in the responsiveness of the smooth muscle surrounding the blood vessels.

That's an important distinction because it suggests repeated heat exposure may actually change how the vascular endothelium responds to increased blood flow.

The hot water wasn't simply making blood vessels temporarily wider while participants were sitting in it. The researchers were measuring vascular function several days after the final session.

In fact, post intervention testing was performed three to five days after the final exercise or hot water session specifically to minimize the influence of acute effects.

That makes the result considerably more interesting.

Heat Therapy May Be Especially Useful When Exercise Is Difficult

This may be the most practical application of the study.

Some older adults simply can't perform enough exercise to create a meaningful cardiovascular training stimulus.

Joint pain, obesity, mobility limitations, cardiovascular disease, neurological conditions, or poor exercise tolerance can make traditional aerobic training difficult.

The researchers specifically designed this study with that problem in mind.

They concluded that hot water immersion may represent a safe and feasible intervention for people with overweight or obesity who have reduced mobility or difficulty adhering to traditional exercise programs.

That's a much more useful way to think about heat therapy.

Not:

"What can I do instead of exercising?"

But:

"What additional cardiovascular stimulus can we provide when exercise is difficult or limited?"

Those are completely different questions.

Exercise Still Wins

I want to make this especially clear because I can already imagine how this research could get marketed.

Hot water immersion improved one measure of vascular function.

That's interesting.

But aerobic exercise improves far more than vascular endothelial function.

Exercise can improve aerobic capacity, mitochondrial function, glucose regulation, insulin sensitivity, muscle function, physical capacity, body composition, mental health, and numerous other physiological systems.

The authors themselves make this point directly.

Exercise remains fundamental for broader vascular adaptations and overall health improvements.

A hot bath doesn't improve your VO2 max because you sat there sweating.

It doesn't strengthen your legs.

It doesn't improve running economy.

It doesn't replace the mechanical and metabolic stimulus of moving your body.

Heat can complement exercise. It doesn't duplicate it.

Could Heat Be Useful in Addition to Exercise?

This study didn't test that question.

Participants performed either aerobic exercise or hot water immersion. There wasn't a group that did both.

So we can't use this paper to say that combining exercise and hot water would have produced greater vascular improvements.

However, from a practical standpoint, that's probably the more interesting question for healthy active people.

If you're already exercising regularly, the goal shouldn't be to replace a training session with a hot bath because one vascular measurement improved similarly in a small clinical study.

The more interesting possibility is whether repeated heat exposure could provide an additional cardiovascular or heat adaptation stimulus on top of training.

This particular study can't answer that.

And I wouldn't pretend that it does.

What About Sauna?

This study used hot water immersion, not sauna.

That's important.

The participants sat in 40°C water with much of the body submerged, including the arms. Water transfers heat to the body much more efficiently than air, and immersion also creates hydrostatic pressure that influences venous return and cardiovascular function.

That means you can't simply translate:

40 minutes in 104°F water

into:

40 minutes in a sauna at some arbitrary temperature.

Both are forms of heat therapy, but they're different physiological interventions.

There is separate research examining sauna exposure and cardiovascular health, but this study specifically tells us about hot water immersion.

That distinction matters.

Don't Turn 104°F Into 110°F Because More Must Be Better

There's another predictable mistake people make whenever they see research like this.

If 104°F worked, 106°F must work better.

And if 106°F works better, why not 110°F?

That's not how this works.

The intervention researchers actually studied was 40°C, or 104°F, for up to 40 minutes under supervision.

There is no evidence from this experiment that making the water hotter would improve the vascular response.

There is, however, a pretty obvious reason not to keep increasing temperature: heat stress can cause dizziness, dehydration, drops in blood pressure, and potentially fainting.

The researchers specifically mention the risk of postural hypotension and falls in older populations and recommend supervision for higher risk and clinical populations.

More heat isn't automatically more health.

The Study Was Small

There are some important limitations here.

Only 31 participants completed the study, with just 11 people in the exercise group, 11 in the hot water group, and nine controls.

That's not a large randomized trial.

The participants were also a specific population: inactive older adults with overweight or obesity. We shouldn't automatically assume the same magnitude of improvement would occur in a healthy 25 year old endurance athlete.

Someone who already exercises regularly may have considerably better baseline endothelial function and therefore less room to improve.

The researchers also acknowledge that the exercise and heat interventions didn't progress in exactly the same way. Exercise intensity progressively increased, while water temperature remained constant and only session duration changed.

Finally, this was a 12 week study.

It tells us something about short term vascular adaptations. It doesn't tell us whether the benefits continue increasing over years or whether hot water immersion ultimately reduces heart attacks, strokes, or cardiovascular mortality.

Those are much bigger questions.

What I Would Actually Take From This Study

If you're physically capable of exercising, exercise should still be the foundation.

That's not particularly close.

But I also wouldn't dismiss heat therapy as nothing more than relaxation.

This study adds to a growing body of evidence suggesting that repeated passive heat exposure can provide a legitimate cardiovascular stimulus.

If someone has difficulty exercising because of mobility limitations, joint problems, obesity, or poor exercise tolerance, hot water immersion may provide a way to stimulate vascular function while gradually working toward greater physical activity.

For active people, I think the more interesting role is potentially as an adjunct to exercise, rather than a substitute for it.

And if you wanted to replicate the intervention that was actually studied, it was pretty simple:

104°F water.

Approximately 40 minutes.

Three times per week.

For 12 weeks.

Just remember that this is the protocol researchers tested. It isn't a universal prescription, and people with cardiovascular disease, blood pressure problems, medications affecting blood pressure, or other medical conditions should be particularly careful with prolonged heat exposure.

The Bottom Line

Can sitting in hot water improve cardiovascular health?

Apparently, at least in some ways, yes.

In this randomized controlled trial, inactive older adults with overweight or obesity completed either aerobic exercise, hot water immersion, or no intervention for 12 weeks.

Both exercise and hot water immersion significantly improved brachial artery endothelial function.

Exercise improved brachial FMD by approximately 1.0 percentage point, while hot water immersion improved it by approximately 0.5 percentage point, and the difference between those improvements was not statistically significant.

But exercise also significantly improved femoral artery endothelial function, while hot water immersion did not. Neither intervention produced clear improvements in resting blood pressure or arterial stiffness.

So no, sitting in a hot tub isn't the same as riding a bike.

But repeatedly exposing your body to heat isn't physiologically meaningless either.

Heat increases blood flow. Increased blood flow increases shear stress. Repeated shear stress can stimulate the blood vessels to adapt.

That's real physiology, and this study provides some pretty interesting evidence that those adaptations can occur after something as simple as sitting in hot water three times per week.

Just don't use it as an excuse to stop exercising.

The hot tub can help your arteries. It still won't do your cardio for you.

Reference:

Costa JG, Locatelli JC, Wigati KW, Naylor LH, Jones H, Haynes A, Green DJ. Comparison of exercise training and repeated hot water immersion on vascular function in overweight older adults. Experimental Physiology. 2026. doi:10.1113/EP094115.