Hot tubs can improve insulin effectiveness, heart health and lower blood pressure in people with type 2 diabetes, research from the University of Portsmouth has found.

The small-scale study involved immersing 14 participants with type 2 diabetes in 40°C water for one hour, eight to 10 times within a two-week period.

Results from the study were split into two separate papers, which have been published in the Journal of Thermal Biology and the American Journal of Physiology.

It's the first study of its kind to show that participants experienced improved insulin sensitivity, which means the insulin they produced worked better after repeated immersion. Glucose levels didn't change, but insulin levels were lower.

Dr. Ant Shepherd, corresponding author on the research from the University's School of Psychology, Sport and Health Sciences, said, "People with diabetes have high levels of sugar, which is what characterises the disease. What we want to do as scientists is to lower those sugar levels.

"There are ways in which we can do this, such as diet and exercise, or prescribing drugs. But although these treatments are effective, there can be barriers, which means other treatments are urgently needed.

"While research on hot water therapy is still limited, this study has clearly found that being immersed in a hot tub made the participants' bodies more sensitive to insulin.

"The pancreas is like a battery; you can only produce so much insulin and at some stage—particularly in those with type 2 diabetes—it will run out. If we can make people more insulin sensitive, producing less, it's far better for the pancreas long-term."

The study took place in a controlled laboratory setting where researchers could monitor the participants' deep body temperature, as well as blood pressure and heart rate every 15 minutes, to ensure safety.

The researchers aimed for participants to reach a target inner body temperature of 38.5 to 39°C, while immersed up to their collar bones.

Lead author, Dr. Thomas James, said, "We also found that participants were burning less calories during the study, which means they were more efficient at rest. This might sound bad, but if their bodies are more efficient at rest, it likely means we've improved their ability to cope with physical activity like walking up the stairs and playing with grandchildren.

"And the hope is that if they're finding low intensity exercise easier, they might be encouraged to do more."

The hot tub treatment was also found to make the heart work easier and lower blood pressure.

Thomas added, "The exposure to hot temperatures made the body work better, but not just while the participants were sitting in a hot tub—we also saw the heart having to work less hard days after they'd been immersed."

The reason for this is when the body is exposed to heat, it has to adapt by lowering our resting body temperature. The body achieves this by reducing the amount of energy we burn at rest. When we use less energy, we also need less oxygen to be delivered around the body by the heart.

"This means the heart doesn't have to work as hard to keep the body supplied with enough oxygen," explained Thomas.

"And when the heart is pumping less blood around the body, it also reduces the pressure inside our blood vessels. It's a bit like when you turn down the water flow from a hosepipe, the pressure inside the hose decreases.

"While further research is needed, this study highlights an exciting possibility for managing type 2 diabetes with innovative heat therapy. We hope these findings could potentially extend to improved well-being, improved blood sugar control and better heart health for individuals with the disease."

As the study had a limited sample size, more comprehensive research with a larger participant group is required to fully grasp the broader implications of hot tub therapy on diabetes management.