Researchers at Texas State University in San Marcos and the University of Texas at Austin found evidence of improvement in vascular health in middle-aged people who went to hot Bikram yoga classes three times per week for 12 weeks.
However, they found the same improvement in a middle-aged group that completed the same Bikram yoga program in a normal-temperature environment.
Bikram yoga is a system of yoga that takes its name from Bikram Choudhury, who started teaching it at his school in India more than 50 years ago. It is now taught by a worldwide network of affiliated teachers.
The system is based on 26 postures, or asanas, and two breathing exercises drawn from traditional hatha yoga. It is known as "hot yoga" because it requires that practice takes place at a room temperature of around 40°C and a relative humidity of 40–60 percent.
Heat not necessary for vascular improvement
The findings follow previous research in which the team found evidence that Bikram yoga can benefit vascular health in middle-aged adults.
"The new finding from this investigation," says first and corresponding study author Dr. Stacy D. Hunter, of the Department of Health and Human Performance at Texas State University, "was that the heated practice environment did not seem to play a role in eliciting improvements in vascular health with Bikram yoga."
The researchers assessed changes in vascular health using a noninvasive method called brachial artery flow-mediated dilation (FMD).
Changes in brachial artery FMD reflect changes in the linings of arteries that are linked to the development of heart disease.
If the measure rises, it can indicate delayed development of atherosclerosis, which is a condition wherein arteries narrow and get stiff due to plaque build-up. This can increase the risk of heart attack and stroke.
Three weekly Bikram classes for 12 weeks
The study participants, whose ages ranged between 40 and 60 years, were 52 "sedentary but apparently healthy adults."
They were all randomly assigned to one of three groups: a hot Bikram group; a normal-temperature Bikram group; or a non-practicing, or sedentary, group that did not participate in the classes to act as controls.
In the hot Bikram group, 19 participants completed 12 weeks of Bikram yoga classes held three times per week. The classes took place in rooms kept at 40.5°C.
In the normal-temperature Bikram group, 14 participants completed the same classes except that their rooms had a normal temperature of 23°C.
The instructions and sequence of the 26 yoga postures and breathing exercises were the same in both the hot and normal-temperature Bikram classes.
Vascular benefit from practicing asanas
The results showed that brachial artery FMD increased over the 12 weeks in both the hot and normal-temperature Bikram groups, whereas there was no change in the control group.
The researchers conclude that the vascular benefits of Bikram yoga seem to stem more from practicing the asanas and less from the heated environment.
They suggest that the findings are "of clinical significance given the increased propensity toward heat intolerance in aging adults."
The results also showed that body fat percentage reduced more in the hot yoga group than in the normal-temperature group.
However, the study authors note that this change was "relatively small and may not have had significant physiological impact."
"This is the first publication to date to show a beneficial effect of the [Bikram yoga] practice in the absence of the heat."
Dr. Stacy D. Hunter