Welcome toShow Me the Evidence,where we go beyond the frenzy of daily headlines to take a deeper look at the state of science around the most pressing health questions of the day.

First period, 8:45 am, a circle of high school students sits so quietly that all you can hear is the whirl of computer fans.

Todays lesson: attention to breathing.

Just notice your breath, says the instructor, Satyani McPherson, where it manifests in the body and the abdomen. ... And whatever is appearing, just allow it to be there.

A student walks in late, and the door slams. No one moves. Eyes are closed. Fourteen chests rise and fall.

****

The juniors and seniors in this international baccalaureate class at Eastern Senior High School in Washington, DC, are stressed out. I asked Raven Wright, a senior, to list all the things she has deal with in a given day. Be on time. Homework. Applications. Scholarship essays. Two jobs: Chipotle and Macys. Mentoring a younger student. Driving lessons. Exhausting.

Once a week for a semester, as part of their IB philosophy class Theory of Knowledge, Wright and her classmates take a break from classwork to meditate. Eastern is one of hundreds of K-12 schools many of them in urban areas, attended mainly by minority students who qualify for free school lunch in the US participating in an unconventional, informal experiment in training students to become more focused and less reactive.

Anecdotally, the students at Eastern love it. Mindfulness is gonna stay with me for the rest of my life, Alayza Mitchel, a student who struggles with the autoimmune disease lupus, says. Especially with the fact of me being a lupus patient and always having to hear news about how it is going to affect me. With mindfulness, she says she can just take a moment to process feelings.

Teachers and administrators at schools like Eastern have welcomed it too. They see mindfulness as a powerful new skill to offer students, not just to manage stress but also to keep them from acting out.

The companies and foundations largely responsible for introducing mindfulness programing into schools tout its psychological benefits such as reduced stress and increased attention. And they say the evidence for mindfulness is based on decades of scientific research.

But research quality is not the same as quantity. And considering that more and more US schools are embracing it, I decided to take a look through the literature: What does the science actually say about mindfulness in kids?

I read more than a dozen studies including systematic meta-reviews, which account for thousands of other papers analyzing the best available research on mindfulness (in both students and adults) and talked to researchers and advocates involved in the work. I asked these experts what questions and concerns parents should have when they hear mindfulness is coming to their schools. (Scroll down for those questions.)

The short of it: The relatively few studies we have on mindfulness in schools suggest a generally positive effect on decreasing anxiety and increasing cognitive performance. But the hype around mindfulness also seems to be outpacing the science, especially when it comes to teaching these practices to children.

Mindfulness is about noticing. Noticing your breathing. Noticing how your emotions manifest in your body. The essence of mindfulness is just tolerating experiencing sensations that come into your body, other than trying to get [them] to stop immediately, Jeff Bostic, a child and adolescent psychiatrist at Georgetown University, says. The one fundamental concept thats shared by all the branches [of mindfulness practice] is the awareness that you accept sensations ... and that you can make sense of what triggered them.

You can think of mindfulness as state of mind, an ability, and a practice. It can be traced all the way back to the early teachings of Buddhism (though its not exclusive to Buddhism). And it has an immediate intuitive appeal in a world thats more distracting and fast-moving than ever before.

Mindfulness is now taught in hospitals and Silicon Valley corporate seminars, and is popular on the TED circuit. More than 14 million people have downloaded the Headspace app for its simple 10-minute meditation exercises. Theres an entire academic journal, Mindfulness, devoted to its study.

There are spiritual, philosophical, and cultural dimensions to this movement, for sure. But researchers from fields ranging from neuroscience to psychiatry have been fascinated by it too. According to Bostic, mindfulness attenuates the more evolutionarily primitive areas of our brains the amygdala, the brain stem, etc. the areas that provoke us to fight, be frightened, or flee, and turn up activation in our frontal lobes, the reasoning center.

Mindfulness is thought to have wide-ranging effects, from lessening depressive symptoms to reducing anxiety and helping to deal with chronic pain and trauma. There are studies that find mindfulness reduces the levels of the stress hormone cortisol. Neuroimaging studies have shown increases of brain matter density in regions linked to learning and memory (though we cant always assume more brain matter equals better). And some behavioral studies find increases in working memory and decreases in mind wandering.

Whats less well understood is how effective it is as an intervention in other words, if you want to use it to change mental health or behavior.

Video from our trips to Eastern High School in Washington, DC.

In the 1970s, Jon Kabat-Zinn, a molecular biologist at University of Massachusetts and practitioner of Zen Buddhist mediation, began developing a mindfulness program for adults in clinical settings. He called it mindfulness-based stress reduction (MBSR), and designed an eight-week course to teach participants how to deal with the pain and stress of chronic illness thats still very popular today.

Throughout the 80s and 90s, mindfulness continued to grow as a complement to traditional medicine and pain management. And it started to make its way into schools in ad hoc, idiosyncratic ways, says Oren J. Sofer, senior program manager at Mindful Schools, which provides mindfulness training instruction for educators. Theres still no formal, national accreditation for mindfulness instruction in schools. But it's become a bit more centralized.

Today mindfulness enters schools through several routes. There are regional-based nonprofits like Minds Incorporated in the DC area that offer mindfulness instruction (sometimes free of charge) to local schools. There are national organizations such as Mindful Schools, which has trained around 14,000 educators and professionals who work with youth in mindfulness instruction (the starter course costs $125). And its being written into textbooks from publishers like Scholastic.

Some schools are even trying it as an alternative approach to discipline.

At Robert Coleman Elementary in Baltimore, students are sent to a Mindful Moment room in lieu of traditional detention. When students enter the room decked out with tie-dye tablecloths and purple beanbags staff from a nonprofit called the Holistic Life Foundation ask students to explain what happened. Then they practice breathing or yoga with the students though sometimes they just play a game. School officials have told reporters the mindful moment room has helped reduce the number of suspensions.

Mindfulness clearly has attracted a lot of buzz. Were almost getting to the point now where the efficacy is taking for granted, said Timothy Caulfield, who studies health and public policy at the University of Alberta and is skeptical of the research.

So to really know if mindfulness training works for kids, for adults, for anyone we need to zoom out a bit and look at the sum of the research we have.

When researchers want to evaluate an intervention like mindfulness, here are the main questions they ask:

1) Does days or weeks of mindfulness instruction lead to any reductions in psychological stress?

2) Is mindfulness any more effective than other stress reduction therapies?

3) Does it work in the school setting?

4) If it does work, why?

5) Is the research high quality, well controlled, and free of bias?

Lets start with the first question.

In 2014, JAMA Internal Medicine published an exhaustive systematic review on mindfulness studies that looked at measures of psychological stress and well-being. In all, the studies included 3,500 adult participants. The analysis included studies that used mindfulness-based stress reduction, transcendental mediation, or mantra-based techniques, and tracked participants on a variety of outcomes like anxiety, depression, and stress scores.

One of the biggest criticism of mindfulness that I kept encountering in reporting: Its all kind of vague.

The results of the JAMA meta-review were generally positive. These programs seem to slightly move the needle on anxiety and depressive symptoms to a degree comparable with what would be expected from the use of an antidepressant in a primary care population, the study concluded.

But heres a caveat: The analysis found that mindfulness was no more effective than other wellness interventions like exercise, muscle relaxation, or cognitive behavioral therapy.

This is a glass-half-empty or half-full type of finding. On one hand, it could mean mindfulness training is as effective as these other treatments. On the other hand, it doesnt show that its magical, said Caulfield.

Overall, at this point in time, the quantity and quality of evidence on mindfulness practices is pretty weak. The JAMA study authors started out with a huge stack of 18,000-plus citations on mindfulness in the literature. But only 47 of those studies had a methodology strong enough to be included in the trial.

The modest benefit found in the study ... begs the question of why, in the absence of strong scientifically vetted evidence, meditation in particularly and complementary measures in general have become so popular, especially among the influential and well educated, Allan Goroll, a professor of medicine at Harvard, wrote in a commentary published alongside the JAMA paper.

So if you want to see the effectiveness of mediation, youd compare people who received instruction for a few weeks with those who did not. Right? The problem is that you cant have the control group do nothing. What if the benefit of being in a mindfulness program is derived from spending time in a classroom setting? Or just paying attention to an instructor?

These variables are really hard to control for, but researchers try by having the control groups engage in some other activity like educational programming, which takes the same amount of time and relative level of engagement. Other studies use active controls, where participants do exercise, undergo massage, or do some other type of therapy where theres an expectation of getting better.

But even with these controls, its still hard to control for peoples expectations. Its not like a clinical drug trial where the control and experimental groups are taking an identical-looking pill. In these studies, people know what group theyve been sorted into. It could be that people who get sorted into mindfulness groups expect greater improvements and are then likely to tell their evaluators they improved. (These studies largely rely on participant self-reports in their data collection.)

"If it is being presented as a worldview, or almost as a philosophy ... thats one thing. But the problem is that it is increasingly being framed as an intervention.

There's nothing wrong with placebo effects except that they often aren't enduring, says James Coyne, emeritus professor of psychology in psychiatry at the University of Pennsylvania (and a vociferous critic of psychological research methods).

The mindfulness literature also suffers from other methodological limitations. Studies vary greatly in the populations of their subject pools the JAMA review included studies on alcoholics, asthma sufferers, and people who have a constant ringing in their ears as well as in the dosage of the treatment (how long and how often participants train), and in the type and quality of the instructions. Which makes it hard to understand if mindfulness gains in one group will generalize to another. There are a lot of variables at play.

A recent PLOS One study found evidence that the whole field of mindfulness studies suffers from publication bias that is, a tendency for only positive results to be reported, leaving contradictory evidence collecting dust in researchers file drawers.

The PLOS authors McGill University psychologists did a systematic review of the literature, finding 124 randomized controlled studies on mindfulness. Ninety percent of the studies showed positive results, which is a lot higher than youd expect given the small sample sizes used in the mindfulness studies. (The percentage of positive results should, according to their calculations, be closer to 65 percent.)

The authors also took a look at mindfulness studies whose methods were registered before the trials began. (Preregistration is now seen as a research best practice, as it limits researchers ability to skew conclusions after the data comes in.) They found 21 registered trials, but only eight of these locked-in study designs yielded publishable results. That suggests that many studies that go unregistered and do not find positive results are simply forgotten.

Im not against mindfulness, Brett Thombs, an author of the study, told Nature. I think that we need to have honestly and completely reported evidence to figure out for whom it works and how much.

(A note: Mindfulness research is hardly the only field of psychological study that suffers from publication bias. Researchers throughout social and biomedical sciences are amid a revolution to demand more rigorous data collection procedures.)

Okay. The JAMA analysis only covered research on adult subjects. What about research on kids? It seemed from my time at Eastern High School that the kids were benefiting from the instruction, at least anecdotally.

Yarnetta Leonard, 17, an Eastern student, says the mindfulness class is helping her manage sad and angry feelings. After the woman who was raising her in southern Virginia died, Leonard was forced to move to DC to live with her biological mother. Coming here, being in a space where I can just think instead of retaliate and be mad and be sad I can think of my actions and do better for myself, she says.

High schools like Eastern where the kids are mostly of color and qualify for free school lunch are commonly targeted for mindfulness interventions. And increasingly, theres high-quality research on whether mindfulness programs can help.

Over the past few years, Erica Sibinga, pediatrician who was one of the co-authors on the JAMA study, and her colleagues at Johns Hopkins, have been conducting well-controlled trials of using mindfulness in some of Baltimores poorest public schools, which would have a lot to gain from a program that reliably reduces stress.

Thats because the chronic stress of growing up poor puts kids at a disadvantage for long-term well-being. Its thought that chronic stress from poverty, from violence, from lack of good nutrition activates cellular pathways that make our bodies more prone to inflammation and less able to fight off infections. Some studies suggest people who grow up poor are even more susceptible to the common cold later in life. If were able to provide youth with tools that may reduce the negative impact of trauma that may potentially have long lasting effects, Sibinga says.

What is not answered is whether the true contribution is the mindfulness practice itself.

She and her colleagues recently conducted a randomized clinical trial with 300 fifth- to eighth-graders in two Baltimore city schools. Half the students got mindfulness instruction for 12 weeks. The other half got 12 weeks of health education, and were the studys controls. Sibinga and her colleagues tried hard to match the instructors for both the health class and the mindfulness class in terms of engagement and skill level. They tried to make the health class engaging and exciting.

Here, mindfulness seemed to move the needle. On depression, [students] moved from the borderline concerning levels to the normal level, Sibinga explains. Does that mean each kid in the intervention group has moved? No, it doesnt. But the average has moved. The study found similar improvements in anxiety levels, self-hostility, coping, and post-traumatic symptoms.

Again, thats only one study. I only found two recent systematic reviews on the use of mindfulness and meditation practices in schools. Like the JAMA study with adults, they generally find positive results, but note methodological flaws in the literature.

A 2014 review published in Frontiers in Psychology found, across 24 studies (11 which had not been published in peer-reviewed journals), that mindfulness improved measures of cognitive performance but had less of an impact on stress and coping.

What we see from the data, people who suffer, whether they are kids or whether they are adults, they profit the most, say Harald Walach, a psychologist who studies complementary medicine in Germany and who was co-author of that review. They are at a low point, and from the low point it is always going upward. If you have kids with real emotional problems, you would likely see a larger effect than if you have normal kids who are doing well at school and have a good family background.

A second 2014 meta-analysis published in Education Psychological Review looked at 15 studies of school meditation programs (which included transcendental mediation as well as mindfulness), and found school based meditation is beneficial in the majority of cases, but the majority of effects of mediation upon student outcomes are small.

Because mindfulness sessions are composed of a grab bag of activities concentrating on breathing, concentrating on sounds, group discussions of the mind-body connection its hard to know what, exactly, the mechanism for these positive changes is, and if that mechanism is unique to mindfulness.

What is not answered is whether the true contribution is the mindfulness practice itself, Walach says. The effect could be from just taking time out from the normal classroom schedule, or taking part in a group activity, or being taught by an inspired teacher. Or do you need all of that together that, we dont know, because it hasnt been studied very well, he says.

And thats one of the biggest criticism of mindfulness that I kept encountering in reporting: Its all kind of vague. Mindfulness a collection of disparate concentration activities targets broad regions in the brain and broadly helps people on a number of things.

It may look like its all over the place , Sibinga admits. But it may be whats changing is upstream of all of those things. By upstream, shes talking about overall systemic changes in the brain or in patterns of thinking. The uncertainties dont scare her away from the research. We know our whole body and brain and mind function together, she says. But we dont know exactly how. Im fascinating by that question. It makes me think we need to explore it further.

She hopes more schools that are inviting in mindfulness training will also invite in those from the research community to study it.

Nothing is for everyone. The same goes for mindfulness.

Though the researchers and studies I consulted agree that its basically harmless, I asked Sibinga, the pediatrician, if there are any cases where kids shouldnt be involved with mindfulness programs. The cases are rare, but she says schizophrenics and people suffering from other thought disorders are not advised to seek out mindfulness training, as it may not be helpful to be mindful about thoughts or delusions that dont have any basis in reality.

The other contraindication is for people who have suffered a severe recent trauma. Their ability to compartmentalize and wall that [trauma] off is closely related to their ability to cope, she says. Mindfulness can be an invitation to tear down those mental walls too soon. (And thats why its important, she says, for mindfulness instructors and students to be well trained, and to look out for these vulnerable youth.)

Do we as adults and educators in society have a responsibility to teach children to be self-aware? You dont need a research study answer that question.

Researchers have also been looking into potential negative effects of mindfulness. One 2015 study in Psychological Science found that 15 minutes of mindfulness instruction made study participants (college undergrads) more susceptible to forming false memories.

In the case of this study, the participants were shown a list of words like garbage, waste, can, refuse, and sewage. Participants who did mindfulness training were more likely to misremember reading the word trash, which is similar to those words but didnt actually appear on the list.

Why? The authors guess when you turn your thoughts inward during meditation, you may be more likely to mix up reality with imaginative assumptions. Mindfulness meditation appears to reduce reality-monitoring accuracy, the authors of the paper concluded. (Its unclear how practically significant misremembering one word on a list is for classroom instruction. Perhaps if students are daydreaming, Brent Wilson, the UC San Diego psychological researcher who led the study, says, theyll have trouble telling if a thought came from the daydream or the teacher.)

And then, finally, some people just dont enjoy introspection, especially when it comes to negative emotions. It is not uncommon for participants in mindfulness interventions to report various unpleasant reactions, such as agitation, anxiety, discomfort, or confusion, during formal mindfulness training exercises, a 2016 review of the state of the field reported. (Though dealing with tough emotions is a core feature of the therapy, not a bug.)

The state of the evidence here is frustrating. Overall, theres evidence that suggests mindfulness has a positive effect for kids on anxiety and cognitive measures. But the research isnt clear on why, whom its most beneficial for (a recent small study found mindfulness training may work better in women), or whether the effect is specific to mindfulness instruction.

There's a lot we still have to learn about what we're doing, Tish Jennings, a professor of education at the University of Virginia, says. Shes generally in favor of mindfulness, and has used it with teachers to help them cope with the stress of their demanding jobs. But she cautions that theres still a lot we dont know.

Such as: How long do the effects last? And in what populations? Whats developmentally appropriate for kids of different ages? What types of meditations are more effective than others?

Often those of us who are developing these programs, we combine a lot of these [meditation] activities, because we're not exactly sure which one is going to work for what person, she says. Because the other thing we don't know is [whether] some people might benefit more from one kind of activity than another.

Mindfulness is an interesting and experimental approach to providing kids with a way to reduce stress. But its not a home run.

Its okay to keep an open mind about this stuff; we just need to be really careful not to hype the potential benefits associate with it, Caulfield says. It would be great if something as simple and straightforward as mindfulness really did have all these incredible benefits, but were not there yet. When it comes to programs touting mental health benefits for youth, he says, we should demand a high bar of evidence.

Oren J Sofer, the senior program manager at Mindful Schools, disagrees with skeptics thinking that its too soon to bring mindfulness meditation into schools. You can overstate the research and make claims that havent been validated, but saying that its experimental I believe is understating the research, he says. I think its important to research this stuff, but at the same time, I think its important to have common sense. Do we as adults and educators in society have a responsibility to teach children to be self-aware? You dont need a research study answer that question.

Throughout my conversations, I had a lingering question: Does mindfulness need to have a scientifically approved psychological benefit for it to be useful or interesting for students? Its not just a psychological technique. Its a philosophy: a way of approaching life. At Eastern High School, teacher Rebecca Milner welcomed it into her classroom because it complemented the curricula she teaches Eastern philosophy in her course. A little stress reduction is an added benefit.

We dont demand humanities instruction have double-blind placebo strength evidence before teachers assign students to read Hamlet. Teachers assign Hamlet because its a great piece of literature that invites students to think about the characters, history, and the English language. Hamlet is taught because it is interesting to think about Hamlet. Mindfulness could be something similar: a toolset for a new, interesting way of thinking about the body, mind, and our emotions.

If it is being presented as a worldview, or almost as a philosophy or an approach to relaxing, thats one thing, Caulfield says. But the problem is that it is increasingly being framed as an intervention. If theyre making claims about specific clinical benefits, I do think we need research to support it. Or present it as experimental or possibly beneficial.

But heres the thing: Mindfulness instructors also like to avoid telling students about the religious and philosophical roots of these practices. And so they lean on the science in their pitches. We deal with [the religious issues] by being transparent and bringing in the science, says Bruce Gill, executive director of Minds Inc., the DC nonprofit that provided the mindfulness programming for Eastern High School. (To the organizations credit, the website does caution that much research is still to be done. And Gill was sure to point out the bulk of formal research has been done with adults.)

Should these open questions prevent further research efforts in schools? No. Not at all. If mindfulness is truly useful in reducing stress in children and adolescents, we should know that. There needs to be more high-quality research like Sibingas to better understand how this affects kids. (Theres a large randomized controlled study underway in 76 UK schools involving around 6,000 students, which should help.)

So parents should be mindful and ask some questions when mindfulness training comes to their school district. The experts I talked to suggested a few:

At the very least, Sibinga says, this research is a recognition is that children really need balance in their school day, and the notion of teaching for the test and trying to cram full the day with only academic work is limited.

If the benefit of mindfulness is simply taking time out of a busy school day, and just remembering to breathe, thats not such a bad thing.

Byrd Pinkerton and Liz Scheltens contributed reporting.

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