A study recently published in the journal Experimental Psychology reveals that it's the yoga, not the "hot" part that is of benefit. Specifically focusing on Bikram hot yoga practice, researcher Stacy Hunter, an assistant professor in the department of health and human performance at Texas State University says: "It’s definitely showing benefits to the 26-posture sequence (practiced in a Birkam session). It just doesn’t seem like the heat is necessary in terms of improving heart health.”
In the study, 52 healthy but previously sedentary adults were assigned to a group: 19 people went to three hot Bikram yoga classes per week, while 14 took the exact same classes in a 73-degree room. A control group of 19 people didn’t do any yoga at all. After 12 weeks, the researchers assessed everyone’s vascular health by looking at changes in endothelial function, or the ability of blood vessels to dilate in response to increased blood flow. Both yoga groups saw changes that indicated a lower risk of heart disease, while the control group did not.
The heat of "hot" yoga did not appear to be responsible for any of the yoga benefit. In fact, previous research has indicated that the high heat and humidity may be detrimental as it raises the body's internal temperature to unsafe levels.