Matthew J. MaleyID, Andrew P. HuntID, Ian B. Stewart, Steve H. Faulkner, Geoffrey M. Minett.
Institute of Health and Biomedical Innovation, School of Exercise and Nutrition Sciences, Queensland
University of Technology, Brisbane, Australia.
Department of Sport and Exercise Science, University of Portsmouth, Portsmouth, United Kingdom.
Department of Engineering, School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom
Objective: Passive heating (PH) has begun to gain research attention as an alternative therapy for cardio-metabolic diseases. Whether PH improves glycemic control in diabetic and non-diabetic individuals is unknown. This study aims to review and conduct a meta-analysis of published literature relating to PH and glycemic control.
Methods: Electronic data sources, PubMed, Embase and Web of Science from inception to July 2018 were searched for randomized controlled trials (RCT) studying the effect of PH on glycemic control in diabetic or non-diabetic individuals. To measure the treatment effect, standardized mean differences (SMD) with 95% confidence intervals (CI) were calculated.
Results: Fourteen articles were included in the meta-analysis. Following a glucose load, glucose concentration was greater during PH in non-diabetic (SMD 0.75, 95% CI 1.02 to 0.48, P < 0.001) and diabetic individuals (SMD 0.27, 95% CI 0.52 to 0.02, P = 0.030). In non-diabetic individuals, glycaemic control did not differ between PH and control only (SMD 0.11, 95% CI 0.44 to -0.22, P > 0.050) and a glucose challenge given within 24 hours post-heating (SMD 0.30, 95% CI 0.62 to -0.02, P > 0.050).
Conclusion: PH preceded by a glucose load results in acute glucose intolerance in non-diabetic and diabetic individuals. However, heating a non-diabetic individual without a glucose load appears not to affect glycemic control. Likewise, a glucose challenge given within 24 hours of a single-bout of heating does not affect glucose tolerance in non-diabetic individuals. Despite the promise PH may hold, no short-term benefit to glucose tolerance is observed in non-diabetic individuals. More research is needed to elucidate whether this alternative therapy benefits diabetic individuals.
Frequent passive heating (PH), often referred to as Waon therapy, hot-tub therapy or thermal therapy, may provide health benefits for those who are in diseased and non-diseased states. Chronic use of Finnish saunas (80 ̊C– 100 ̊C air, < 20% relative humidity) is associated with a reduced risk of dementia, stroke, respiratory disease, hypertension, fatal cardiovascular and all-cause mortality event. The mechanisms responsible for how PH maintains. health in those free of disease and improves health in diseased conditions are not completely clear. Current evidence suggests PH elicits improvements in shear patterns (increase in ante-grade shear), microvascular function (endothelial-dependent), lipid profiles, reduced arterial stiffness and blood pressure, as well as reduced heart rate and deep body temperature during heat stress; responses that are also evident, albeit to a greater extent, following regular physical activity.