Heat Therapy and Cardiometabolic Health in Obese Women (CMH)

Traditional medical treatments are often based on research done exclusively in males, and recent research efforts in the physiology community have highlighted critical sex differences in disease presentation and progression. For example, the relative risk of fatal heart disease is 50% greater in obese, diabetic women as compared to their male counterparts, and women appear to respond differently to lifestyle interventions such as exercise compared with men. Chronic passive heat exposure (hot tub use) provides alternative or supplemental therapeutic potential for improving cardiovascular and metabolic health in obese women. In addition, passive heat exposure may offer specific cellular protection from stresses like a lack of blood flow (ischemia), which is the primary cause of fatal coronary heart disease. This study is investigating the possible cardiovascular and metabolic health benefits of chronic passive heat exposure, and whether regular hot tub use (3-4 days per week for 8-10 weeks) may reduce obese womens' cardiometabolic risk. The investigators are examining cardiovascular health through blood pressure, blood vessel stiffness, sympathetic ('fight or flight') activity, and responsiveness to stresses like increased or decreased blood flow. The investigators are also examining metabolic health through an oral glucose tolerance test and a subcutaneous fat biopsy. The goal of this research is to develop a therapy targeted toward the specific health needs and complications of obese women, in an effort to improve cardiovascular and metabolic health and provide therapeutic alternatives in this high-risk population.

Obesity, Polycystic Ovary Syndrome, Prehypertension, PreDiabetes, Cardiovascular Risk Factor, Metabolic Syndrome

heat therapy, blood pressure, oral glucose tolerance test, adipose tissue, muscle sympathetic nerve activity

Subjects were matched for age and BMI, then assigned to either a heat therapy intervention or time control (no intervention, just outcomes assessment at matched timepoints).

It was not possible to blind the subject or PI to treatment group, but all measures that were collected were analyzed offline by a blinded investigator.

Subjects assigned to heat therapy underwent 30 1-hour hot tub sessions over 8-10 weeks (3-4 per week). The hot tub was set to 40.5 Celsius, and core temperature and heart rate were monitored throughout each session.Subjects were instructed to not make any other dietary or lifestyle changes.Cardiovascular and metabolic health assessments were made Pre (0 heat sessions), mid (after 14-16 heat sessions, ~4-5 weeks), and post (after all 30 heat sessions; ~8-10 weeks).

Subjects were monitored at matched timepoints (start of study, 4-5 weeks, and 8-10 weeks) but not exposed to any intervention. Subjects were instructed to not make any dietary or lifestyle changes.

flow-mediated dilation of brachial artery, expressed as % change in diameter. A measure of endothelial function.

flow-mediated dilation of brachial artery, expressed as % change in diameter, following 20 minute ischemia-20 minute reperfusion. A measure of vascular tolerance to ischemia-reperfusion stress.

Adipose tissue sample analyzed for insulin signaling, markers of inflammation, and heat shock protein expression

Inclusion Criteria: Age 18-40 Body mass index (BMI) between 30-45 kg/m2. Willing to maintain consistent diet and activity patterns through the study Willing to refrain from food, physical activity, supplements, and medications as required before testing days Willing to refrain from blood donations over the course of the study Exclusion Criteria: overt cardiovascular disease or diabetes medications that affect blood vessel function (i.e. Spironolactone), insulin sensitivity (Metformin), or blood coagulation (i.e. Warfarin) Recent rectal, anal, or vaginal surgery pregnant, breastfeeding, or trying to conceive within 6 months.