Book review: ‘The Science of Yoga: The Risks and the Rewards’


Who knew yoga could be so dangerous? Or is the risk overblown?

A woman falls asleep in seated forward fold and damages both sciatic nerves. A man sits on his heels for hours (over a period of days or weeks) and deadens nerves in his lower legs. A woman practices Kapalbhati — forceful exhaling — and collapses a lung. A woman attempting the wheel — essentially, making the body arc like a croquet wicket — balances on her head, bends her neck backward and suffers a stroke.

Author William J. Broad, a yogi since 1970 and the chief science writer for the New York Times, remains devoted to the practice. He has much to say about yoga’s benefits to mind and body, its ability to relieve depression and improve one’s sex life. He details yoga’s history, its charlatans and the occasional sexual predator.

But his chapter on bizarre injuries will get the most attention. By my count, he cites six cases from medical literature dating to 1973 and alludes to more. He describes anecdotal cases and his own excruciating back injury.


His six examples from medical journals include three strokes — one linked to shoulder stand, one to headstand and one to the wheel. Broad explains the risk cogently: Yoga postures that include “extreme bending of the neck” can cause a clot in the vertebral arteries, triggering a rare type of stroke that tends to strike young, healthy people.

How great is the risk? When he tries to quantify yoga injuries, the most common seem to be orthopedic: lower back, shoulder, knee and neck. Not that those aren’t painful, as Broad himself can attest.

“My research has prompted me to change my own routine,” Broad writes. “I have deemphasized or dropped certain poses, added others, and in general now handle yoga with much greater care.”

I get that. Since reading this book, I’ve been congratulating myself on avoiding shoulder stand, a pose I detest. (Broad outlines a way to make it safer by using blankets – a traditional Iyengar method. This doesn’t work for everyone, however.) And an Ashtanga version of headstand puts weight on the forearms rather than the head. Broad mentions this method but not its lineage.

Yoga is not risk-free but strokes seem to be exceedingly rare. The truth is, injuries happen in any human activity — running, playing tennis, even getting out of bed. Staying sedentary carries risks too, including heart disease. In the six years I’ve practiced yoga, my worst injury came as I walked home: I stepped in a hole, fell flat on my face, broke a couple of teeth and bit my lip clean through.

Forget freaky injuries, however: Modern urbanites’ true terror is gaining weight. Broad finds that yoga does not raise metabolism; in fact it lowers it. Nor does yoga improve physical conditioning like aerobic exercise. (But more vigorous forms of yoga, such as vinyasa flow, might do better. Yoga studies are themselves rare, since drug companies have no reason to pay for them.)


Lowering metabolism sounds like a bad thing, but it contributes toward a major benefit of yoga: boosting moods. What Broad calls the best study on yoga and physical conditioning stumbled upon that angle.

The experiment at Duke University Medical Center, published in 1989, included about 100 people: a control group, a group that used stationary bicycles and a group of yogis. After four months, the bicyclists had improved their conditioning and the yogis had not — but they believed they had.

The yogis “reported enhanced sleep, energy, health, endurance and flexibility,” Broad writes. “They described how they experienced a wide range of social benefits, including better sex lives, social lives and family relationships. ... They had better moods, self-confidence and life satisfaction.”

Two later studies by scientists from Boston University School of Medicine, Harvard Medical School and McLean psychiatric hospital showed that yoga boosted brain levels of the neurotransmitter gamma-aminobutyric acid. Low GABA levels have been linked to depression.

As for sex, Broad finds that yoga raises testosterone levels and lowers the level of cortisol, a stress hormone. Another yoga practice, rapid breathing, can boost arousal. You don’t need pills or twin bathtubs.

Some practioners think of yoga as a path to enlightenment. This book can be enlightening for yogis and nonyogis alike.