 "Can hot water baths mimic exercise? Study says they might do better")
Hot water baths may be better for your heart and immunity than saunas, new research suggests.
Scientists from the University of Oregon found that immersing the body in hot water improves blood flow, lowers blood pressure, and activates immune responses more effectively than sitting in a traditional or far-infrared sauna.
The study, titled Comparison of Thermoregulatory, Cardiovascular, and Immune Responses to Different Passive Heat Therapy Modalities and published in the American Journal of Physiology, indicates that regular hot-water immersion could offer some of the same health benefits as exercise by raising core body temperature, enhancing blood flow, and stimulating immune activity.
According to the scientists, hot water transfers heat more efficiently than air, making it harder for the body to cool down. When submerged up to the chest, the body can’t rely on sweating to shed excess heat, forcing it to adapt in other ways.
This thermoregulatory stress boosts blood circulation, expands blood vessels, and strengthens cardiovascular function. In the study, participants’ core temperatures rose by about 1.1 degrees Celsius in hot water, by 0.4 degrees Celsius in a traditional sauna, and by no significant change in a far-infrared sauna.
The study authors explained that increasing body temperature causes an increase in blood flow, and just the force of blood moving across vessels benefits vascular health.
What health effects did researchers observe?
The study involved 20 healthy adults (10 men and 10 women, aged 20–28). They alternated between three heat therapies:
- Hot water immersion: 45 minutes at 40.5 degrees Celsius
- Traditional sauna: three rounds of 10 minutes at 80 degrees Celsius, with short cooling breaks
- Far-infrared sauna: 45 minutes at 45–65 degrees Celsius
Hot water immersion produced the strongest cardiovascular and immune responses:
- Heart rate increased by 39 beats per minute on average
- Cardiac output (blood pumped per minute) rose by 3.7 L/min
- Blood pressure dropped by about 14 mmHg
- Immune markers such as interleukin-6 (IL-6), natural killer (NK) cells, and CD8+ T cells increased—effects typically seen after moderate exercise
Can heat therapy really mimic exercise?
The study suggests it can. The cardiovascular load of hot water immersion, like elevated heart rate, dilated blood vessels, and increased circulation, is comparable to what happens during a brisk walk or light jog.
This makes heat therapy a promising option for people who cannot exercise due to injury, age, or chronic illness. While it’s not a substitute for movement, it can supplement fitness or serve as an entry point to improving heart and metabolic health.
The researchers noted that only hot water immersion activated the immune system. It raised IL-6, a signalling molecule that spikes during exercise to trigger anti-inflammatory responses later. Participants also saw increases in natural killer cells, which fight infections, and cytotoxic T cells, key players in immune defence.
This “mini fever” effect, where the body warms itself and boosts immune surveillance, may explain why regular sauna or bath users report fewer colds and better recovery after exertion.
Who should avoid hot water therapy?
According to the study, heat therapy is generally safe for healthy individuals when done moderately. However, it may not suit those with:
- Heart disease
- Pregnancy
- Uncontrolled high blood pressure
The researchers stressed that hydration is crucial during heat therapy. Participants in the study drank water freely during the sessions. Overheating can cause dizziness or fatigue, so sessions should be kept short (20–45 minutes) and always followed by cooling down. For more health updates, follow #HealthWithBS
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