According to a survey, Yoga in America, there are now almost 37 million yoga practitioners in the United States — up from just 20 million in 2012. And another 80 million people responded that intended to take up the practice for the first time in the near future.

When people were asked why they started doing yoga:

• 61 percent answered that they did it for improved flexibility

• 56 percent said for stress relief

• 49 percent said general fitness

• 49 percent said to improve overall health

• 44 percent said for physical fitness.

There’s no question that many people believe that yoga is good for them. But what does science tell us about its health benefits?

Dr. Dov Michaeli, M.D., Ph.D., starts his review of yoga health benefits by examining breathing. Science has demonstrated that breathing slowly and deeply has many physiological effects, he says. And we even understand to a large degree how it exerts some of its effects.

The brain is bathed in a liquid called cerebrospinal fluid (CSF). Significant CSF flow has been shown to occur exclusively with inspiration, in particular during forced deep breathing. On the other hand, breath-holding suppresses it.

“These results have unambiguously identified inspiration as the most important driving force for CSF flow in humans,” writes Michaeli.

Because CSF plays an important role in clearing toxins out of the brain, it follows that increased CSF flow related to yoga breathing will help the brain get rid of waste products.

The brain’s respiratory centers, located in the brainstem, are responsible for involuntary aspects of breathing. Examples include the response to changes in blood pH that suggest an accumulation of CO2, as well as increases in respiratory rate in response to a scary event (the “fight or flight response”).

These centers are also influenced by voluntary changes in breathing. Studies show that yoga deep breathing is associated with the appearance of theta waves in the brain. These waves are characteristic of deep relaxation and sleep states.

According to Michaeli, “Deep, slow breathing also affects the reward system of the brain and seems to un-clutter the areas that participate in rational thinking and decision making.”

You can read Dr. Michaeli’s full article, Proven Health Benefits of Yoga, on The Doctor Weighs In.