Meditation-based therapies for stress, anxiety and depression have been making a comeback since the 1990s. Mindfulness meditation, in particular, has so thoroughly infiltrated mainstream psychiatry that mindfulness-based approaches have been called the "Third Wave of Behavior Therapies." At this point, there isn't too much question about whether mindfulness meditation is helpful for distress. The main focus for researchers now is why and how it works, and through what mechanism.
Does meditation improve depression by improving sleep? Being a clinical psychologist with an interest in both depression and sleep, I have spent the last several years investigating whether meditation-related improvements might be mediated by improvements in sleep. The idea seemed obvious: Poor sleep is a symptom of depression and it is also a risk factor for developing depression or relapsing. Meditation techniques, including mindfulness, have been found to calm the sympathetic nervous system's "fight or flight response" and decrease worry and rumination -- all the things that interfere with good sleep. But does meditation improve sleep? My first thought was "of course!"
Like any good American, I went online and Googled "Meditation + Sleep" and came up with nearly six million hits, the majority praising the sleep-promoting effects of meditation ("Meditation, a natural sleep aid") and selling meditation-based sleep products ("Achieve a better night's sleep with meditation techniques") -- many from medical professionals ("Sleeplessness? M.D. offers self-help tips and sleep meditation CD").
Based on the internet, it looks like meditation is great for sleep. Time to take a closer look at the scientific research...
How to Evaluate the Claims: Not All Research Is Equal
There are two general types of meditation studies: cross-sectional studies and longitudinal studies. Cross-sectional studies compare experienced meditators with non-meditators and are good place to start, but they can have hidden confounds that can obscure firm conclusions.
For example, if you compared a group of regular exercisers to non-exercisers and found that they were healthier, it would be easy to conclude that exercise makes you healthy. But what is not known is whether the exercisers also eat healthier diets, smoke or drink less or if the non-exercisers had a pre-existing health problem that prevented them from exercising.
The same problem applies to cross-sectional studies of meditators; it is unknown if the meditators were happier, less stressed or better sleepers before they started meditating, or whether they engage more in other health-promoting behaviors. Because of this, researchers put more value in longitudinal studies that measure sleep before and after learning meditation in people who have never meditated before.
It's also important that the longitudinal study is a "randomized controlled trial," or RCT, where half of the subjects are randomly allocated to the meditation group and the other half don't meditate. This helps control for effects that are based on expectancy (hope of trying something new) or increased familiarity with the measures over time.
A Review of the Science Comes up Lacking
When I followed up the enthusiastic Google claims on the scientific research database Medline, the evidence was less compelling. Only a handful of longitudinal studies had investigated the effects of mindfulness meditation on sleep. Nearly all the studies found an improvement in self-reported sleep following meditation, but when a control group was added, the meditation group didn't improve more than the control condition, which was usually a wait-list.
What was even more discouraging about the existing research was that they relied on self reports -- either a general rating of sleep quality, or an average of daily diaries. None of the studies used what is considered the "Gold Standard" of sleep research, the polysomnographic sleep study, which measures brainwaves (EEG), eye-movements and muscle tone overnight in a laboratory.
The next step was obvious: Do a longitudinal randomized control trial with laboratory-based polysomnographic sleep measures in a depressed population with sleep complaints. Twenty-six medication-free individuals with a history of depression were randomized into either an eight week mindfulness meditation program called "Mindfulness-based Cognitive Therapy" or a wait-list control condition. All participants underwent in-lab sleep recordings before and after the treatment condition and filled out daily sleep diaries.
Meditation and Sleep Diaries Equally Beneficial for Self-Reported Sleep
According to sleep diaries, self-reported sleep improved following mindfulness meditation, just like in the other studies. But again, when compared to the control group, the effect disappeared. Filling out daily sleep diaries (but not meditating) was just as beneficial for sleep as meditation. When the act of measurement changes what is measured, we call that the "Hawthorne Effect." In this case, increased attention to daily sleep habits may have changed the participants' perception of their sleep quality or subtly encouraged them to adapt healthier sleep schedules. Thus, confirming previous studies, it does not appear that mindfulness meditation is especially good for improving (self-reported) sleep.
Results from the Sleep Lab
Even though the meditators said they were sleeping better, results from laboratory-based sleep and brain recordings told a different story. Contrary to our hypotheses that meditation would improve and deepen sleep, we found that meditation was associated with several indices of increased wakefulness and decreased sleep propensity, including more awakenings and stage one sleep (a lighter stage of sleep) and less stage three and four or "slow-wave sleep" (a deeper stage of sleep) compared to controls.
Even more compelling was the dose-response relationship between meditation practice amount and increases in wakefulness: the more one meditated, the more awake one's brain became.
Paradox and Promise
Before we jump to the conclusion that meditation makes sleep worse, it is important to mention that the increased wakefulness in the brain was associated with improvements in depression. The people who meditated the most (at least 30 minutes per day) had more wakeful brains and were less depressed, but also reported sleeping better. Interestingly, this paradoxical pattern of improvements in self-reported sleep and mood with a corresponding increase in brain wakefulness is also seen in depressed patients who respond positively to SSRI's like Prozac.
Like most research, these findings provoke many more questions than they answer, but it's important not to speculate and to stick to the original question: Does meditation improve sleep? Our results, along with other longitudinal studies -- which have only examined mindfulness meditation and not other techniques -- do not support the widespread claims that meditation promotes better, deeper sleep. Much more research is needed. The take home message is that sometimes popular enthusiasm outpaces scientific research, and consumers should be as educated as possible about how to evaluate the evidence.
Tip: Always go to the original source: A detailed scientific report of this study can be found here.