A rise in body temperature, sweat and heart rate — these physical responses are the most common signs of a strenuous aerobic workout. But these same physiological reactions are also strikingly similar to the ones you experience soaking in a hot bath.
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That's what the authors of a December 2020 review published in the Journal of Applied Physiology concluded. They also discovered that regular hot baths could offer many of the same health benefits as moderate-intensity exercise.
In fact, one small study in the review found that two months of cycling (three times a week for 30 minutes) compared to the same number of time-matched warm baths produced comparable improvements in cardiorespiratory fitness and vascular health in young sedentary male adults.
But does that really mean you can skip your spin class for some time in the tub and still reap the same benefits? Here, John Higgins, MD, a sports cardiologist with McGovern Medical School at UTHealth in Houston, assesses the benefits of a hot bath — and their limits — versus exercise.
5 Hot Bath Benefits
When compared to moderate-intensity exercise, regular hot baths have many of the same health pluses.
1. They Improve Blood Flow and Blood Pressure
It's well documented that exercise has protective effects on vascular health. But research also points to similar advantages of hot baths.
For example, a June 2016 study in The Journal of Physiology found that eight weeks of regular hot baths helped reduce arterial stiffness and reduced blood pressure in young sedentary adults.
"Hot baths increase blood flow not only to skin but also to other vital organs," Dr. Higgins says. This boost in blood flow promotes the production of more nitric oxide, which keeps the blood vessel walls smooth and prevents inflammation and plaque build-up, he explains.
The increased dilation of blood vessels also leads to a lowering in blood pressure, Dr. Higgins adds.
2. They Increase Your Heart Rate
Just like a brisk jog, stepping into a hot bath will raise your heart rate.
Here's why: A steamy bath causes the blood vessels to dilate and lowers your blood pressure. Consequently, "your heart rate speeds up to compensate," Dr. Higgins says.
Indeed, the same review in the Journal of Applied Physiology found that passive heating (such as taking a hot bath) can increase heart rate between 20 to 40 beats per minute. Still, it's worth noting that this effect is substantially milder compared to the rise that occurs during moderate-intensity exercise.
3. They May Help Reduce Inflammation
Exercise can help curb chronic low-grade inflammation — which drives many diseases — and there's some evidence that regular hot baths can have a similar benefit.
Hot bathing can decrease inflammatory markers, which may reduce your risk of cardiovascular morbidity and mortality by as much as 25 percent, Dr. Higgins says. But the long-term effects of hot baths on inflammation aren't certain and more research is needed.
4. They Promote Better Blood Sugar Levels
Research has found that just three weeks of daily hot bathing can improve blood glucose levels in people with type 2 diabetes, Dr. Higgins says.
For instance, a July 2015 study in Current Opinion in Clinical Nutrition and Metabolic Care found that heat therapy, such as using a sauna or hot tub, shows some promise in treating type 2 diabetes.
The extreme heat can cause your blood vessels to dilate, which makes your body absorb insulin more quickly and as a result, lower blood sugar levels, according to the Centers for Disease Control and Prevention.
5. They Can Help Boost Mood
Anyone who's ever experienced a runner's high or the feel-good rush of post-workout endorphins can confirm — exercise can boost your mood.
Apparently, so can a hot soak. Warm baths may reduce stress hormones and help balance serotonin levels, which play a role in regulating mood, according to the Cleveland Clinic.
In addition, some research shows that bathing in hot water (104 degrees Fahrenheit) for a half-hour can help decrease depression symptoms, per the Cleveland Clinic.
3 Limits of Hot Baths
While hot baths may mimic some of the health benefits of exercise, there are certain things they simply can't do. Here are a few:
1. They Don’t Build Muscle, Strength or Bone Density
Exercise puts force on a muscle, leading to muscle damage and subsequent repair and growth (as well as increased bone density), Dr. Higgins says.
But you can't build lean muscle and sturdy bones or make strength gains by relaxing in a hot bath. "To build and strengthen muscles, you have to use them," Dr. Higgins says.
2. They Don’t Enhance Endurance
Though a hot bath can raise heart rate temporarily, it can't help you sustain physical activity for an extended period. In other words, it won't support your stamina.
To improve your endurance, you must increase the distance, time or difficulty of an exercise, and this does not happen with a hot bath, Dr. Higgins says.
3. They Don’t Support Weight Loss
While working out can be part of a healthy weight loss (or weight management) strategy, a steamy soak in the tub won't foster fat loss or lower your BMI.
Case in point: The same Journal of Applied Physiology review found that eight weeks of moderate-intensity cycling reduced body weight whereas hot baths did not. That may be because aerobic exercise burns more than 10 times the calories as passive heating.
When to Take a Hot Bath for the Best Benefits
The best time to reap the benefits of a hot bath is right after a workout, Dr. Higgins says. Thirty minutes in the tub can soothe sore muscles and support muscle recovery and growth.
That's because hot baths improve blood flow, which helps repair and rebuild muscle fibers and reduce inflammation, Dr. Higgins says.
For an even greater bang for your bath buck, add Epsom salts, which can help loosen muscles and alleviate pain, per the Cleveland Clinic. Three hundred grams should do the trick.
For the optimal hot bath benefits, aim to take a hot bath four times weekly and soak for 30 to 60 minutes, Dr. Higgins says.
While there are many benefits of taking a hot bath, they can also dry out your skin. To avoid this, don’t soak in steamy water every day. And try these tips:
- Use a hydrating soap.
- Limit your lathering to your face, underarms and groin.
- Moisturize as soon as possible to lock in the moisture.
So, Can Hot Baths Replace Exercise?
"The best way to think about a hot bath is (pardon the pun) like a watered-down version of exercise," Dr. Higgins says. With a hot bath, you get some of the vascular benefits of exercise, but not the major cardiorespiratory or cardiometabolic gains of moving your body.
So, if you only have 30 minutes in your schedule, going for a jog or taking an aerobics class will always be better than 30 minutes of lying in a hot tub, Dr. Higgins says.
In other words, hot baths should not be used as a substitute for exercise but rather as a complement to your regular workout regimen.
- Cleveland Clinic: “4 Reasons to Take a Bath”
- Journal of Applied Physiology: “The health benefits of passive heating and aerobic exercise: To what extent do the mechanisms overlap?”
- Centers for Disease Control and Prevention:"10 Surprising Things That Can Spike Your Blood Sugar"
- The Journal of Physiology: "Passive Heat Therapy Improves Endothelial Function, Arterial Stiffness and Blood Pressure in Sedentary Humans"
- Current Opinion in Clinical Nutrition and Metabolic Care: "Heat Shock Proteins and Heat Therapy for Type 2 Diabetes"