Hot water and blood pressure...a study reveals the size of the connection

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After a busy day at work, we may only need some relief from warm water, but the body may gain more than that. As fatigue subsides, tiny blood vessels under the skin expand, more blood flows through them, and blood pressure may also decrease.

In a recent study, researchers observed this effect after participants spent half an hour in hot water. Blood pressure decreased to a greater extent than after riding a stationary bike for the same period.

The study, published in the European Journal of Applied Physiology, included 25 overweight or obese adults, aged between 45 and 70, who engaged in less than 150 minutes of structured exercise per week.

Tiny blood vessels under the skin play an essential role in regulating body temperature, supplying tissues with oxygen and nutrients and helping to eliminate waste. When the body temperature rises, these vessels expand, and more blood flows near the surface of the skin, which helps dissipate heat.

While exercise contributes to improving the functions of blood vessels and their inner lining, the effect of exposure to heat without exerting physical effort still requires further research, especially in elderly people who are overweight or obese.

Based on this, the researchers sought to compare the microvascular response to hot water with their response to moderate exercise, and monitor the accompanying changes in blood pressure.

Participants had two sessions in random order, separated by at least 72 hours. In one, they sat in 40°C hot water for 30 minutes. The other involved riding a stationary bike for the same amount of time, bringing the pulse to between 60 and 70 percent of the maximum heart rate.

The participants' resting blood pressure did not exceed 140/90 mmHg, while the heart rate did not exceed 100 beats per minute.

To know the effect of each activity, the researchers tracked blood pressure, pulse, and body temperature. They also used an imaging technique known as optical coherence tomography, which allows the tiny blood vessels under the skin of the forearm to be seen without surgical intervention, to determine how wide they are, the speed of blood, and the amount of blood flowing through them.

The results showed that sitting in hot water decreased systolic pressure by an average of 6 millimeters of mercury, and diastolic pressure by about 10 millimeters.

In contrast, the changes after cycling were smaller; The upper number rose by one millimeter of mercury, while the lower number decreased by two millimeters.

In addition, the team observed greater expansion of microvessels and an increase in blood flow after sitting in hot water. It is likely that this response is directly related to the effect of heating the skin, in addition to an increase in body temperature.

However, the trial measured the immediate effect of a single session of each activity, and did not prove that the pressure reduction would persist or achieve similar benefits with repeated bathing. Also, the two sessions were equal in duration, but they differed in the amount of thermal impact on the body.

Therefore, the results open the way to study hot water immersion as a possible means of supporting physical activity programs, especially for people who find it difficult to exercise, without considering it an alternative or a proven treatment for high blood pressure.

The researchers stressed the need for more studies to determine the feasibility of this approach, and whether the immediate changes they observed could translate into sustainable benefits for vascular health.