Judge Eleni Derke cuts an imposing figure, shrouded in her black robe and seated behind the elevated wood-paneled bench in the county courthouse in Jacksonville, Florida. From the jury box and lawyers’ tables, you can’t see what else she’s wearing: wildly patterned yoga pants.

More than 25 years ago, Derke discovered yoga. She was suffering from the searing abdominal pain of Crohn’s disease. Her doctor recommended surgery. Hoping to avoid it, she went to see a cousin who was a yoga master. He taught her the upside-down poses known as inversions. They are said to clear the body of toxins, though there’s no scientific evidence to support the claim. Derke’s symptoms quickly subsided. “Yoga saved my life.”

She trained as a yoga instructor, and if it’s not too hot, she holds free monthly classes on the courthouse lawn. When lawyers drone on at trial, she will order a break and lead jurors in standing stretches and breathing exercises. But she’s best known in legal circles as the judge who sentences offenders to take yoga behind bars.

Derke handles misdemeanors, such as shoplifting, minor drug possession, and driving under the influence, punishable by up to a year in jail. Offenders can cut their time by 40 percent or more if they take a weekly program called Yoga 4 Change. She sees yoga as a way to quiet self-defeating chatter in the mind and quell rage, fear, anguish, and compulsions that drive bad behavior.

“Once you let go,” she said, “you make room for the positive things.” Her colleagues, though, didn’t buy it at first. “Come on, yoga?”

Many offenders had a similar reaction. “I thought it was really weird,” said Cecil Reddick, an inmate at Jacksonville’s Montgomery Correctional Center.

An evaluation of the program in three Jacksonville facilities found that after six weeks, participants reported significant improvements in sleep, overall health, and the ability to manage anger and anxiety. At least two more county judges now offer the yoga option.

Some offenders choose to do their full sentence rather than try yoga, but Reddick grabbed the get-out-of-jail-quick offer from one of Derke’s colleagues. He was surprised by how much the classes relaxed him, soothed his sore back, and stirred a sensation he’d never felt: “Serenity.”

Yoga, a spiritual practice that began in India, has extended its limbs widely. In the United States, it’s held up as a fitness regimen, a path to transformation or enlightenment, and a treatment for so much that ails us—from addiction, headaches, and hearing loss to post-traumatic stress disorder, heart disease, and yes, Crohn’s.

More than 14 percent of U.S. adults used yoga for health reasons in 2017, up from 9.5 percent five years earlier, a government survey found. Since 2018, Harvard Medical School students have studied it as part of a required course on building resilience. Parents tote infants to Itsy Bitsy Yoga, which purports to improve a baby’s sleep, digestion, and brain development.

Validating health claims for yoga is difficult. Most studies involve too few participants to be conclusive, in large part because yoga does not generally attract big government grants or have an industry like drugmakers to finance research.

Sat Bir Singh Khalsa, a yoga instructor, Harvard neuroscientist, and expert on the science of yoga, acknowledges the research has a long way to go. “But I would say we have demonstrated our credibility.” Khalsa has investigated yoga for insomnia, PTSD, anxiety, and chronic stress, where he’s seen the most compelling evidence of yoga’s benefits.

Stress plays a major role in many illnesses that kill us. It also drives unhealthy eating, poor sleep, alcohol and drug misuse, and other bad habits. “Modern medicine really sucks at preventing chronic disease,” he said.

Khalsa, who took up kundalini yoga in 1971, told me with excitement that epigenetics and neuroimaging are revealing how the body and brain interact—and unraveling the mysteries of yoga’s power. In other words, the benefits aren’t just in a devotee’s mind.

Researchers in Norway analyzed blood from 10 volunteers before and after two-hour sessions of a yoga practice with rhythmic breathing and saw significantly increased gene activity in circulating immune cells. Scientists at UCLA studying breast cancer survivors discovered yoga decreased the expression of genes involved in inflammation, believed to be a root of many complex diseases.

Scientists at the National Institutes of Health found that longtime yoga practitioners don’t display the usual age-related declines in the brain’s gray matter. Yogis also had larger volume in several brain regions, including the hippocampus, critical to memory and emotional regulation, and the precuneus and posterior cingulate cortex, involved in attention and self-awareness.

Studies like these bring scientific legitimacy, but they’re not why the ancient discipline has caught on in a frazzled, fast-paced society. “Yoga is a strategy for making people basically happy and able to cope with modern life,” Khalsa said.

This may be the moment to admit that yoga stressed me out. I went on the recommendation of a physical therapist who had healed my injured shoulder after others had failed. When he spoke, I dutifully listened. In the 2.4-square-mile New York City suburb where I live, yoga is abundantly available in storefront studios, community recreation rooms, the continuing education program, and the chain health club. I started there, accompanied by my husband. Classes were packed. People jostled for space like subway commuters. Supple spandex-clad bodies bent, curled, and twisted in ways that defied me. It felt like one more competitive arena where I didn’t measure up. I took refuge in restorative yoga, where I seemed as adept as anyone at splaying across comfortable bolsters and trying not to snore. Meanwhile, my husband learned to stand on his head.

I’m not the only one to have a hard time reconciling the yoga scene with the potential of a serious practice. “I would get feedback that my playlist wasn’t cool enough,” said teacher Olivia Mead. “I thought, I cannot handle this anymore. I didn’t become a yoga instructor to wear cute shorts. I actually wanted to make a difference.”

Mead founded Yoga for First Responders. The nonprofit has brought yoga to police departments, fire stations, and training academies from Los Angeles to Thunder Bay, Ontario. Classes tailor the traditional yoga elements—physical postures, breath regulation, deep relaxation, and meditation—to help people endure the challenges of putting their lives on the line.

“The whole goal is to harness the mind,” she said, “not to touch your toes.”

Nineteen women wearing identical inmate T-shirts and pants took their spots on mismatched yoga mats arranged in a U-shape in a cramped room at Jacksonville’s Montgomery Correctional Center. Two uniformed officers stood watch over me; one of them, Sgt. Rhonda Warren, held an iPad and videoed my interviews.

It seemed an unlikely setting to release stress, not to mention harness the mind. Kathryn Thomas, a former Navy aviator who founded the nonprofit Yoga 4 Change, led the women through deep inhales and exhales, and then the fluid series of poses known as the sun salutation. Gradually, a sense of calm became palpable.

Most inmates weren’t required to come. Some signed up, as Melissa Bruce told me, “basically to have something to do.” Many wanted a break from the tension and clamor of living among inmates, an hour to sink into oneself. If they hadn’t all achieved enlightenment or transformation, at least a dozen told me they’d learned skills to help them survive another day. Philieza Lopano said she used the breathing exercises and gentle stretches during lockdowns to relieve anxiety.

Watching each woman stretch and fold and blow out her breath in loud, unembarrassed whooshes, it occurred to me that I might have fared better in yoga if I’d focused less on other people and more on myself, without judgment. After the women filed out of the room, I mentioned to Warren that I would try yoga again.

“I know,” she said, nodding slowly. “Me too.”