Hot Tubs Improve A1c, BMI, and Blood Pressure in Type 2 Diabetes

Frequent hot tub bathing had a positive impact on glycemia, blood pressure, and body weight in patients…

Hot Tubs Improve A1c, BMI, and Blood Pressure in Type 2 Diabetes

Frequent hot tub bathing had a positive impact on glycemia, blood pressure, and body weight in patients with type 2 diabetes, in the first real-world study to analyze the effect of this type of heat therapy in such individuals.

“The data from our analysis showed that the frequency of hot tub bathing could have beneficial influences on diabetic control, hypertension, and obesity even after adjusting for confounding factors,” Hisayuki Katsuyama, MD, told Medscape Medical News.

Katsuyama presented the findings as a poster at the virtual European Association for the Study of Diabetes (EASD) Annual Meeting 2020. The study aimed to explore the real-world influence of habitual hot tub bathing on the control of type 2 diabetes and other cardiovascular risk factors.

“Heat therapy, shown here with hot tub bathing, can be one effective therapeutic option for type 2 diabetes in daily life. An alternative form of heat exposure might be nutrition therapy and exercise,” noted Katsuyama, from Kohnodai Hospital, Ichikawa, Chiba, Japan.

But Lucy Chambers, PhD, head of research communications at Diabetes UK, was not so enthusiastic about the results.

“While this research suggests there might a link between taking regular hot baths and better health in people with type 2 diabetes, it raises more far more questions than it answers,” she said.

“It could be that people who bathe more frequently have a healthier lifestyle in general — perhaps they are more physically active — we just don’t know from the limited data collected.”

“It is not possible to say from this research whether bathing can benefit your physical health,” she noted in a statement from Diabetes UK.

Large Study in Over 1000 Participants

Prior to the current study, there were no large studies looking at the effects of hot tub bathing on metabolic parameters in patients with diabetes.

One cohort study in Finland revealed that frequency of sauna bathing was inversely associated with fatal cardiovascular events in middle-aged adults (BMC Med. 2018;16:219). And a prior small before-and-after study in patients with diabetes showed a significant reduction in fasting glucose and A1c (N Engl J Med. 1999;341:924-925), Katsuyama noted.

Most homes in Japan, where bathing is a traditional and common practice, have hot tubs, which prompted the researchers’ idea for a real-world study, he explained.

Katsuyama and colleagues studied the frequency of hot-tub bathing using a self-reported questionnaire completed by 1297 patients with type 2 diabetes who regularly visited Kohnodai Hospital over 6 months.

They took anthropometric measurements and used blood test results to analyze associations between hot tub use and different variables. Patients were divided into three groups according to frequency of bathing: group 1, ≥ 4 baths/week; group 2, 1-<4 baths/week; and group 3, < 1 bath/week.

Mean age was 67 years, weight was 67 kg, BMI was 25.9 kg/m2, and A1c was 7.2%. There were more men than women (713/584).

Most participants, 693, were in group 1 (≥ 4 baths/week), 415 were in group 2 (1-< 4 baths/week); and 189 were in group 3 (< 1 bath/week).

The mean frequency of bathing was 4.2 times/week and mean duration of bathing was 16 minutes.

Body weight, BMI, waist circumference, diastolic blood pressure, and A1c were all significantly better in group 1 (most frequent bathing) compared with group 3 (least frequent bathing) (Table).

Table. Effects of Frequency of Hot Tub Bathing on Metabolic Parameters

Metabolic parameter

Group 1
≥ 4 baths/week

Group 2
1- <4 baths/week
Group 3
< 1 bath/week
P value
Body weight, kg 66.2 67.1 70.0 .026
BMI, kg/m2 25.5 26.0 26.7 .025
Waist circumference, cm 92 94 101 .012
Diastolic BP, mm Hg 73 75 77 .001
A1c, % 7.10 7.20 7.36 .012

BP = blood pressure


Is Heat Stimulation Responsible for Beneficial Effects?

Katsuyama pointed out that animal studies have suggested heat stimulation might improve insulin sensitivity and enhance energy expenditure, an effect also observed during exercise.

“I expect that patients can benefit in a similar way with heat therapy,” he added, noting that hot tub bathing might be particularly beneficial for patients who cannot exercise.

“It would probably [also] be beneficial for the prevention of diabetes,” and potentially, diabetes complications, he said. Indeed, “cohort studies have shown the possibilities that heat therapy could prevent cardiovascular diseases.”

Katsuyama pointed out that a key strength of the study was the relatively large number of participants compared with previous studies.

But there were also limitations due to the nature of the cross-sectional study, which “means we cannot guarantee causality, and secondly, various confounding factors, such as diet and other life habits, could influence the results.”

“A well-designed prospective study will be needed to confirm the beneficial effects of the heat therapy,” he concluded. 

EASD 2020. Presented September 22, 2020. Abstract 342.

Katsuyama has reported no relevant financial relationships.

For more diabetes and endocrinology news, follow us on Twitter and Facebook.