Fifteen years ago, a handful of poorly constructed, clearly biased studies purported to show that prayer was a legitimate medical tool. Americans fell for it. It's hard to resist something we want to believe.
Today, people want to believe that yoga will solve their problems. More than 200 studies were published about the health benefits of yoga last year. Yoga is supposed to cure everything from low back pain to short attention span.
We should, as a nation, revisit the "prayer as medicine" craze annually to remind us of the credulous depths we have plumbed. In 1988, the Southern Medical Journal published a study that asked "born again" Christians to pray for only half of participating patients in a coronary care unit. The study reported that those patients achieved better outcomes than the prayer-deprived. "Prayer to the Judeo-Christian God has a beneficial therapeutic effect," the authors concluded.
Similar studies followed. A 1999 paper in the highly regarded Archives of Internal Medicine claimed that prayer "may be an effective adjunct to standard medical care."
That article caught the attention of skeptical scientists, who decried the absurdity of its methodology. The families and friends of patients in the nonprayer groups probably prayed for them, too, making it impossible to separate the control group from the test group. Does it matter how much time a patient is prayed for or to which God his prayers are directed?
The statistical analysis was also deeply flawed. The prayer group only won out in two of 35 outcomes measures, which is about what you'd expect from random chance. The authors, however, chose to focus on a small number of obscure cardiac outcomes to support their conclusions.
In 2006, a well-constructed study published in the American Heart Journal finally proved that praying to God confers no medical benefit. God's medical career was over. But he left a void in the discussion of medicine, and yoga has filled it. Studies come out on a near weekly basis trumpeting its benefits. Yoga for diabetes. Yoga for high blood pressure. Yoga for cancer. Yoga for slow reactions.
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The yoga studies, however, contain myriad methodological problems, some of which are similar to those that plagued prayer research.
First, what is yoga? That's not a zen koan, but an honest question. In a real, practical sense, medical researchers have to agree on the elements essential to yoga practice before they can test it as a therapy. Is deep breathing or stretching the source of therapeutic benefit? Or maybe it's simple exercise, which wouldn't exactly be news.
In addition, yoga, like prayer, can't be dosed in milligrams. How much yoga do you need to do, and for how long, to achieve a benefit? There's also significant individual variation at play. Some people breathe more deeply, hold poses for longer, and meditate "better" (I assume) than others. That's going to muddy the statistics.
Control and blinding are also problematic. When you test a pill for heart disease, you give some people the pill and others a placebo (or an existing medication). Patients can't tell which group they're in. It's not easy to convince someone that they've been doing yoga for six weeks when they haven't, so the placebo effect is always a problem. And in a surprising number of yoga studies, the researchers aren't blinded, either, raising the risk of a second form of bias.
Take a look at systematic review articles and meta-analyses — studies that aggregate other studies — and you'll see where the miraculous yoga cure really stands.
A systematic review on the treatment of asthma with yoga was published in the Journal of Asthma in 2011. It found that the methodology of the underlying studies was "mostly poor," due to problems with blinding and randomization. In the only study included in the review that offered a credible placebo control — a non-yogic stretching regimen — yoga offered no benefit.
A 2013 review paper on yoga for hypertension complained that the "methodological quality of the included trials was evaluated as generally low," and therefore "a definite conclusion about the efficacy and safety of yoga on (hypertension) cannot be drawn."
To be fair, the folks who review existing studies occasionally do conclude that yoga may have modest benefits for sufferers of some afflictions, but they almost always include a laundry list of gripes about methodology and offer the weakest possible recommendation.
Why haven't you already heard about all of these anti-yoga studies? They have no constituency, and therefore don't interest the media much. When the Journal of Clinical Oncology reported recently that yoga improves quality of life in breast cancer patients came out recently, hundreds of stories trumpeted the news in the mainstream media. Yet it's difficult to find any mention of the review articles discussed above that question the efficacy of yogic practice as a health-care tool.
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This doesn't mean you shouldn't do yoga. By all means, do yoga, pray and eat lemons, if those things bring you contentment. Do yoga especially if it's your preferred form of exercise — exercise is a health intervention supported by thousands of clinical trials. But recognize the "yoga as medicine" craze for what it is: an indicator of the zeitgeist, not a scientific discovery.