Since then, according to a 2015 review by Australian researchers, a few studies of healthy young adults have suggested that hot yoga may be good for the heart. That review turned up evidence that arterial stiffness decreased in one small group of young adults and that insulin resistance declined among a small group of older participants who did Bikram yoga. In a 2011 study of 51 adults, people reported less stress after doing Bikram classes for eight weeks.
People who like hot yoga say they feel better after doing it, though the benefits they report vary among people, who have differing motivations for taking the classes. Among 700 people whom Mace Firebaugh has surveyed in an ongoing study, 48 percent say that hot yoga improves their mood. Forty-seven percent report better flexibility, 34 percent feel less anxiety and 33 percent report clearer skin. Some have reported negative effects such as nausea, dizziness and dehydration, but those symptoms are usually mild.
The survey found another intriguing result: 43 percent of participants reported losing weight as a result of doing hot yoga, but that linkage might be a coincidence. Studies have yet to connect hot yoga with weight loss, the 2015 review found. And as sweaty as a hot-yoga session can be, it may not burn as many calories as people think.
In a 2014 study of 19 experienced Bikram practitioners during a single 90-minute session, Tracy and colleagues found that men burned an average of about 460 calories and women burned about 330. It’s about the same number of calories you’d burn during a brisk walk for the same amount of time, Tracy says. And even though that’s about 50 percent more than what people burn in a typical yoga class, it was much less than what people thought they had burned. (Heart rates peaked above 150 beats per minute during the toughest parts of class — a sign more of the body’s response to heat than of a boost in calorie-burning.)
Even as research begins to point to some potential pluses of hot yoga, it’s not clear whether heat has anything to do with those benefits. Studies on other types of yoga have shown good outcomes, too, including improvements in heart health, range of motion and balance.
Heat’s effects on the body, meanwhile, are complicated. Exercising in the heat carries risks, including heatstroke and dehydration. But emerging evidence, including a long-term study published last year by Finnish researchers, suggests that regular sauna use can lower blood pressure and reduce the risk of heart disease. A 2016 review found that raising body temperature might ease symptoms of depression. And applying heat directly to muscles can increase range of motion.
Whether hot yoga is dangerous remains a contentious question. There have been a few alarming incidents reported during and after hot yoga classes, including the 2016 case of a 35-year-old woman who experienced sudden cardiac arrest during a session.
And a 2015 study reported that people’s core temperatures during Bikram classes could rise above 104 degrees. But that research was flawed, says Tracy, whose 2014 study showed a maximum core temperate of 101.6, with an average rise to 100.3. The danger zone, he says, begins at 102 degrees.
Tracy recommends lying down if you feel lightheaded during a class and giving your body several sessions to acclimate to the heat.
“My big piece of advice for people who want to try hot yoga is to take it slowly,” Tracy says. “If you don’t feel right, take it easy. If a yoga instructor starts yelling at you, remember you’re a human being. You’re not being held hostage.”
People with pre-existing conditions — such as cardiovascular disease, back pain, asthma and diabetes — should consult a doctor before beginning a hot yoga practice, adds Mace Firebaugh. Her own low blood pressure, she suspects, explains why hot yoga doesn’t suit her.
Pregnancy is another time to be cautious, she says. In her survey, she found that nearly a quarter of women who had been pregnant continued practicing hot yoga during their pregnancies. But increased core temperatures in a pregnant mom can be dangerous to a fetus.
“In general, hot yoga is likely safe, and the risks are minimal and mild,” Mace Firebaugh says. “If you love it, do it. If it doesn’t work for you, there’s probably going to be another type of yoga that is going to be fine. Hot yoga might not be for everybody.”