Yoga can be traced back to ancient India, and though research is limited, studies suggest it is safe for most people and may have multiple benefits, including easing chronic low-back pain and improving some heart disease risk factors. But even less is known about hot yoga, a more recent form of the mind-body practice. Hot yoga is performed in a room heated to between 80 degrees and 105 degrees Fahrenheit and may be more physically rigorous than regular yoga, making practitioners susceptible to dehydration and muscle injuries, said Casey Mace, an assistant professor of public health at Central Washington University in Ellensburg, Wash.
“People may assume the warnings and benefits and possible risks are the same for all types of yoga, and that’s simply not true,” said Dr. Mace, who has studied hot yoga. Her research found that hot yoga practitioners reported benefits like greater flexibility and improvements in mood, fitness and stamina, but that over half had experienced dizziness, lightheadedness, nausea or dehydration.
“There may be a misconception that these feelings are normal, but they’re not,” she said. “If people are feeling dizzy or have headaches or feel weak or fatigued, it may be related to fluid loss. They should take a break, cool down and get hydrated. Proper hydration is key.”
Still, Dr. Mace said, “Hot yoga is generally safe, and the side effects we’re seeing are generally mild,” though as with any kind of yoga, the practice does have risks. Doctors in Chicago reported this summer on a case involving a healthy 35-year-old woman who went into cardiac arrest induced by heat stroke during a hot yoga class. The woman survived.
Muscle and joint injuries may be more common with hot yoga because the heat makes people feel more limber than they actually are, and they may overdo it, but data on injuries is also limited, said Carol Ewing Garber, a professor of movement science and kinesiology at Teachers College, Columbia University, and past president of American College of Sports Medicine. “You have to be a bit cautious when you look at studies, because they are conducted with high-quality, well-trained yoga teachers under the best of circumstances,” Dr. Garber said. “The reality is that out in the real world, there is a lot of variability across instructors in terms of their training.”
Research on one form of hot yoga, Bikram yoga, suggests it improves balance, lower body strength and range of motion for both the upper and lower body, and might even help improve arterial stiffness and metabolic measures like glucose tolerance and cholesterol levels, as well as bone density and perceived stress. But the Australian researchers who reviewed the literature — including one who is a co-owner of a Bikram yoga studio — noted that only one randomized controlled trial, the kind considered the gold standard in medicine, had been conducted, and that most studies did not track adverse events and included only healthy adults.
If you have low blood pressure or a pre-existing health condition, consult with a doctor before trying hot yoga. If you have adverse reactions to heat, are prone to heat stroke or dehydration or have a medical reason to avoid being in a hot tub or sauna, you may want to stick with regular yoga. If you are doing a hot yoga class, make sure you’re well hydrated by drinking a lot of water before, during and after class.
“If you’re sweating profusely, it’s very difficult to replenish that fluid,” Dr. Garber said, and many people aren’t good at “recognizing the early signs of heat illness.” These include thirst, profuse sweating, dizziness or headaches, weakness, muscle cramps and nausea or vomiting.