Effects of meditation

A comparison of the effect of various meditation techniques on systolic blood pressure.[1]

In June, 2007 the United States National Center for Complementary and Integrative Health (NCCIH) published an independent, peer-reviewed, meta-analysis of the state of meditation research, conducted by researchers at the University of Alberta Evidence-based Practice Center. The report reviewed 813 studies involving five broad categories of meditation: mantra meditation, mindfulness meditation, yoga, T'ai chi, and Qigong, and included all studies on adults through September 2005, with a particular focus on research pertaining to hypertension, cardiovascular disease, and substance abuse. The report concluded:

Scientific research on meditation practices does not appear to have a common theoretical perspective and is characterized by poor methodological quality. Future research on meditation practices must be more rigorous in the design and execution of studies and in the analysis and reporting of results. (p. 6)

It noted that there is no theoretical explanation of health effects from meditation common to all meditation techniques.[1]

A version of this report subsequently published in the Journal of Alternative and Complementary Medicine in 2008 stated: "Most clinical trials on meditation practices are generally characterized by poor methodological quality with significant threats to validity in every major quality domain assessed." This was despite a statistically significant increase in quality of all reviewed meditation research, in general, over time between 1956 and 2005. Of the 400 clinical studies, 10% were found to be good quality. A call was made for rigorous study of meditation.[3] These authors also noted that this finding is not unique to the area of meditation research and that the quality of reporting is a frequent problem in other areas of complementary and alternative medicine (CAM) research and related therapy research domains.

Of more than 3,000 scientific studies that were found in a comprehensive search of 17 relevant databases, only about 4% had randomised controlled trials (RCTs), which are designed to exclude the placebo effect.[1]

In a 2013 meta-analysis, Awasthi argued that meditation is defined poorly and despite the research studies showing clinical efficacy, exact mechanisms of action remain unclear.[9] A 2017 commentary was similarly mixed,[5][6] with concerns including the particular characteristics of individuals who tend to participate in mindfulness and meditation research.[10]

A 2013 statement from the American Heart Association (AHA) evaluated the evidence for the effectiveness of TM as a treatment for hypertension as "unknown/unclear/uncertain or not well-established", and stated: "Because of many negative studies or mixed results and a paucity of available trials... other meditation techniques are not recommended in clinical practice to lower BP at this time."[11] According to the AHA, while there are promising results about the impact of meditation in reducing blood pressure and managing insomnia, depression and anxiety, it is not a replacement for healthy lifestyle changes and is not a substitute for effective medication.[12]

The term meditation encompasses a wide range of practices and interventions rooted in different traditions, but research literature has sometimes failed to adequately specify the nature of the particular meditation practice(s) being studied.[13] Different forms of meditation practice may yield different results depending on the factors being studied.[13]

The presence of a number of intertwined factors including the effects of meditation, the theoretical orientation of how meditation practices are taught, the cultural background of meditators, and generic group effects complicates the task of isolating the effects of meditation:[14]

Numerous studies have demonstrated the beneficial effects of a variety of meditation practices. It has been unclear to what extent these practices share neural correlates. Interestingly, a recent study compared electroencephalogram activity during a focused-attention and open monitoring meditation practice from practitioners of two Buddhist traditions. The researchers found that the differences between the two meditation traditions were more pronounced than the differences between the two types of meditation. These data are consistent with our findings that theoretical orientation of how a practice is taught strongly influences neural activity during these practices. However, the study used long-term practitioners from different cultures, which may have confounded the results.

In 2011, National Center for Complementary and Integrative Health (NCCIH) released findings from a study in which magnetic resonance images were taken of the brains of 16 participants 2 weeks before and after the participants joined the mindfulness meditation (MM) program by researchers from Massachusetts General Hospital, Bender Institute of Neuroimaging in Germany, and the University of Massachusetts Medical School. The researchers concluded:

... these findings may represent an underlying brain mechanism associated with mindfulness-based improvements in mental health.[36]

The analgesic effect of MM involves multiple brain mechanisms including the activation of the anterior cingulate cortex and the ventromedial prefrontal cortex.[37] In addition, brief periods of MM training increases the amount of grey matter in the hippocampus and parietal lobe.[38] Other neural changes resulting from MM may increase the efficiency of attentional control.[39]

Participation in MBSR programmes has been found to correlate with decreases in right basolateral amygdala gray matter density,[40] and increases in gray matter concentration within the left hippocampus.[41]

Mindfulness meditation also appears to bring about favorable structural changes in the brain, though more research needs to be done because most of these studies are small and have weak methodology.[42] One recent study found a significant cortical thickness increase in individuals who underwent a brief -8 weeks- MBSR training program and that this increase was coupled with a significant reduction of several psychological indices related to worry, state anxiety, depression.[43] Another study describes how mindfulness based interventions target neurocognitive mechanisms of addiction at the attention-appraisal-emotion interface.[24] A meta-analysis by Fox et al. (2014) using results from 21 brain imaging studies found consistent differences in the region of the prefrontal cortex and other brain regions associated with body awareness. In terms of effect size the mean effect was rated as moderate. (Cohen's d = 0.46) However the results should be interpreted with caution because funnel plots indicate that publication bias is an issue in meditation research.[42] A follow up by Fox et al. (2016) using 78 functional neuro-imaging studies suggests that different meditation styles are reliably associated with different brain activity. Activations in some brain regions are usually accompanied by deactivation in others. This finding suggests that meditation research must put emphasis on comparing practices from the same style of meditation, for example results from studies investigating focused attention methods cannot be compared to results from open monitoring approaches.[44]

Psychological and Buddhist conceptualisations of mindfulness both highlight awareness and attention training as key components, in which levels of mindfulness can be cultivated with practise of mindfulness meditation.[45][18] Focused attention meditation (FAM) and open monitoring meditation (OMM) are distinct types of mindfulness meditation; FAM refers to the practice of intently maintaining focus on one object, whereas OMM is the progression of general awareness of one's surroundings while regulating thoughts.[46][47]

Focused attention meditation is typically practiced first to increase the ability to enhance attentional stability, and awareness of mental states with the goal being to transition to open monitoring meditation practise that emphasizes the ability to monitor moment-by-moment changes in experience, without a focus of attention to maintain. Mindfulness meditation may lead to greater cognitive flexibility.[48]

In an active randomized controlled study completed in 2019, participants who practiced mindfulness meditation demonstrated a greater improvement in awareness and attention than participants in the active control condition.[18] Alpha wave neural oscillation power (which is normally associated with an alert resting state) has been shown to be increased by mindfulness in both healthy subjects and patients.[49]

Tasks of sustained attention relate to vigilance and the preparedness that aids completing a particular task goal. Psychological research into the relationship between mindfulness meditation and the sustained attention network have revealed the following:

• Mindfulness meditators have demonstrated superior performance when the stimulus to be detected in a task was unexpected, relative to when it was expected. This suggests that attention resources were more readily available in order to perform well in the task. This was despite not receiving a visual cue to aid performance. (Valentine & Sweet, 1999).
• In a continuous performance task[50] an association was found between higher dispositional mindfulness and more stable maintenance of sustained attention.
• In an EEG study, the Attentional blink effect was reduced, and P3b ERP amplitude decreased in a group of participants who completed a mindfulness retreat.[51] The incidence of reduced attentional blink effect relates to an increase in detectability of a second target. This may have been due to a greater ability to allocate attentional resources for detecting the second target, reflected in a reduced P3b amplitude.
• A greater degree of attentional resources may also be reflected in faster response times in task performance, as was found for participants with higher levels of mindfulness experience.[52]

• Selective attention as linked with the orientation network, is involved in selecting the relevant stimuli to attend to.
• Performance in the ability to limit attention to potentially sensory inputs (i.e. selective attention) was found to be higher following the completion of an 8-week MBSR course, compared to a one-month retreat and control group (with no mindfulness training).[52] The ANT task is a general applicable task designed to test the three attention networks, in which participants are required to determine the direction of a central arrow on a computer screen.[53] Efficiency in orienting that represent the capacity to selectively attend to stimuli was calculated by examining changes in the reaction time that accompanied cues indicating where the target occurred relative to the aid of no cues.
• Meditation experience was found to correlate negatively with reaction times on an Eriksen flanker task measuring responses to global and local figures. Similar findings have been observed for correlations between mindfulness experience in an orienting score of response times taken from Attention Network Task performance.[54]
• Participants who engaged in the Meditation Breath Attention Score exercise performed better on anagram tasks and reported greater focused attention on this task compared to those who did not undergo this exercise.[55]

• Executive control attention include functions of inhibiting the conscious processing of distracting information. In the context of mindful meditation, distracting information relates to attention grabbing mental events such as thoughts related to the future or past.[47]
• More than one study have reported findings of a reduced Stroop effect following mindfulness meditation training.[48][56][57] The Stroop effect indexes interference created by having words printed in colour that differ to the read semantic meaning e.g. green printed in red. However findings for this task are not consistently found.[58][59] For instance the MBSR may differ to how mindful one becomes relative to a person who is already high in trait mindfulness.[39]
• Using the Attention Network Task (a version of Eriksen flanker task [53]) it was found that error scores that indicate executive control performance were reduced in experienced meditators [52] and following a brief 5 session mindfulness training program.[56]
• A neuroimaging study supports behavioural research findings that higher levels of mindfulness are associated with greater proficiency to inhibit distracting information. As greater activation of the rostral anterior cingulate cortex (ACC) was shown for mindfulness meditators than matched controls.
• Participants with at least 6 years of experience meditating performed better on the Stroop Test compared to participants who had not had experience meditating.[60] The group of meditators also had lower reaction times during this test than the group of non-meditators.[60]
• Following a Stroop test, reduced amplitude of the P3 ERP component was found for a meditation group relative to control participants. This was taken to signify that mindfulness meditation improves executive control functions of attention. An increased amplitude in the N2 ERP component was also observed in the mindfulness meditation group, thought to reflect more efficient perceptual discrimination in earlier stages of perceptual processing.[61]

Research shows meditation practices lead to greater emotional regulation abilities. Mindfulness can help people become more aware of thoughts in the present moment, and this increased self-awareness leads to better processing and control over one's responses to surroundings or circumstances.[62][63]

Positive effects of this heightened awareness include a greater sense of empathy for others, an increase in positive patterns of thinking, and a reduction in anxiety.[63][62] Reductions in rumination also have been found following mindfulness meditation practice, contributing to the development of positive thinking and emotional well-being.

Emotional reactivity can be measured and reflected in brain regions related to the production of emotions.[64] It can also be reflected in tests of attentional performance, indexed in poorer performance in attention related tasks. The regulation of emotional reactivity as initiated by attentional control capacities can be taxing to performance, as attentional resources are limited.[65]

• Patients with social anxiety disorder (SAD) exhibited reduced amygdala activation in response to negative self-beliefs following an MBSR intervention program that involves mindfulness meditation practice.[66]
• The LPP ERP component indexes arousal and is larger in amplitude for emotionally salient stimuli relative to neutral.[67][68][69] Individuals higher in trait mindfulness showed lower LPP responses to high arousal unpleasant images. These findings suggest that individuals with higher trait mindfulness were better able to regulate emotional reactivity to emotionally evocative stimuli.[70]
• Participants who completed a 7-week mindfulness training program demonstrated a reduction in a measure of emotional interference (measured as slower responses times following the presentation of emotional relative to neutral pictures). This suggests a reduction in emotional interference.[71]
• Following a MBSR intervention, decreases in social anxiety symptom severity were found, as well as increases in bilateral parietal cortex neural correlates. This is thought to reflect the increased employment of inhibitory attentional control capacities to regulate emotions.[72][73]
• Participants who engaged in emotion-focus meditation and breathing meditation exhibited delayed emotional response to negatively valanced film stimuli compared to participants who did not engage in any type of meditation.[74]

It is debated as to whether top-down executive control regions such as the dorsolateral prefrontal cortex (DLPFC),[75] are required[73] or not[66] to inhibit reactivity of the amygdala activation related to the production of evoked emotional responses. Arguably an initial increase in activation of executive control regions developed during mindfulness training may lessen with increasing mindfulness expertise.[76]

Research has shown stress reduction benefits from mindfulness.[77][78][79] A 2019 study tested the effects of meditation on the psychological well-being, work stress, and blood pressure of employees working in the United Kingdom. One group of participants were instructed to meditate once a day using a mindfulness app on their smartphones, while the control group did not engage in meditation. Measurements of well-being, stress, and perceived workplace support were taken for both groups before the intervention and then again after 4 months. Based on self-report questionnaires, the participants who engaged in meditation showed a significant increase in psychological well-being and perceived workplace support. The meditators also reported a significant decrease in anxiety and stress levels.[79]

Other research shows decreased stress levels in people who engage in meditation after shorter periods of time as well. Evidence of significant stress reduction was found after only three weeks of meditation intervention.[18] Brief, daily meditation sessions can alter one's behavioral response to stressors, improving coping mechanisms and decreasing the adverse impact caused be stress.[80][81] A study from 2016 examined anxiety and emotional states of naive meditators before and after a 7-day meditation retreat in Thailand. Results displayed a significant reduction in perceived stress after this traditional Buddhist meditation retreat.[81]

Chronic insomnia is often associated with anxious hyperarousal and frustration over inability to sleep.[82] Mindfulness has been shown to reduce insomnia and improve sleep quality, although self-reported measures show larger effects than objective measures.[82][83]

A large part of mindfulness research is dependent on technology. As new technology continues to be developed, new imaging techniques will become useful in this field. Real-time fMRI might give immediate feedback and guide participants through the programs. It could also be used to more easily train and evaluate mental states during meditation itself.[84] The new technology in the upcoming years offers many new opportunities for the continued research.

Vipassana meditation is a component of Buddhist practice. Phra Taweepong Inwongsakul and Sampath Kumar from the University of Mysore have been studying the effects of this meditation on 120 students by measuring the associated increase of cortical thickness in the brain. The results of this study are inconclusive.[85][86] Vipassana meditation leads to more than just mindfulness, but has been found to reduce stress, increase well-being and self-kindness.[87] These effects were found to be most powerful short-term, but still had a relatively significant impact 6 months later. In a study conducted by Szekeres and Wertheim (2014), they found stress to be the category that seemed to have the most regression, but the others contained higher prevalence when compared to the participants' original scores that were given from before embarking on Vipassana meditation. Overall, according to self-reports, Vipassana can have short and long-term effects on an individual.

An essential component to the Vipassana mediation approach is the focus on awareness, referring to bodily sensations and psychological status. In a study conducted by Zeng et al. (2013), awareness was described as the acknowledgement of consciousness which is monitoring all aspects of the environment.[88] This definition differentiates the concept of awareness from mindfulness. The emphasis on awareness, and the way it assists in monitoring emotion, is unique to this meditative practice.

Sahaja yoga meditation is regarded as a mental silence meditation, and has been shown to correlate with particular brain[89][90] and brain wave[91][92][93] characteristics. One study has led to suggestions that Sahaja meditation involves 'switching off' irrelevant brain networks for the maintenance of focused internalized attention and inhibition of inappropriate information.[94] Sahaja meditators appear to benefit from lower depression[95] and scored above control group for emotional well-being and mental health measures on SF-36 ratings.[96][97][98]

A study comparing practitioners of Sahaja Yoga meditation with a group of non-meditators doing a simple relaxation exercise, measured a drop in skin temperature in the meditators compared to a rise in skin temperature in the non-meditators as they relaxed. The researchers noted that all other meditation studies that have observed skin temperature have recorded increases and none have recorded a decrease in skin temperature. This suggests that Sahaja Yoga meditation, being a mental silence approach, may differ both experientially and physiologically from simple relaxation.[93]

Kundalini yoga has proved to increase the prevention of cognitive decline and evaluate the response of biomarkers to treatment, thereby shedding light on the underlying mechanisms of the link between Kundalini Yoga and cognitive impairment. For the study, 81 participants aged 55 and older who had subjective memory complaints and met criteria for mild cognitive impairment, indicated by a total score of 0.5 on the Clinical Dementia Rating Scale. The results showed that at 12 weeks, both the yoga group showed significant improvements in recall memory and visual memory and showed significant sustained improvement in memory up to the 24-week follow-up, the yoga group showed significant improvement in verbal fluency and sustained significant improvements in executive functioning at week 24. In addition, the yoga cohort showed significant improvement in depressive symptoms, apathy, and resilience from emotional stress. This research was provided by Helen Lavretsky, M.D. and colleagues.[99] In another study, Kundalini Yoga did not show significant effectiveness in treating obsessive-compulsive disorders compared with Relaxation/Meditation.[100]

The first Transcendental Meditation (TM) research studies were conducted at UCLA and Harvard University and published in Science and the American Journal of Physiology in 1970 and 1971.[101] However, much research has been of poor quality,[1][100][102] including a high risk for bias due to the connection of researchers to the TM organization and the selection of subjects with a favorable opinion of TM.[103][104][105] Independent systematic reviews have not found health benefits for TM exceeding those of relaxation and health education.[1][100][104] A 2013 statement from the American Heart Association described the evidence supporting TM as a treatment for hypertension as Level IIB, meaning that TM "may be considered in clinical practice" but that its effectiveness is "unknown/unclear/uncertain or not well-established".

In another study, TM proved comparable with other kinds of relaxation therapies in reducing anxiety.[100] Practitioners of TM have demonstrated a one Hertz reduction in EEG alpha wave frequency relative to controls.[106]

The medial prefrontal and posterior cingulate cortices have been found to be relatively deactivated during meditation (experienced meditators using concentration, lovingkindness and choiceless awareness meditation). In addition experienced meditators were found to have stronger coupling between the posterior cingulate, dorsal anterior cingulate, and dorsolateral prefrontal cortices both when meditating and when not meditating.[107] Over time meditation can actually increase the integrity of both gray and white matter. The added amount of gray matter found in the brain stem after meditation improves communication between the cortex and all other areas within the brain.[108][109] Meditation often stimulates a large network of cortical regions including the frontal and parietal regions, lateral occipital lobe, the insular cortex, thalamic nuclei, basal ganglia, and the cerebellum region in the brain. These parts of the brain are connected with attention and the default network of the brain which is associated to day dreaming.[110]

In addition, both meditation and yoga have been found to have impacts on the brain, specifically the caudate. Here, there is greater connectivity to the caudate, as well as the interaction of basal ganglia cortico-thalamic feedback loops within meditation and yoga practice.[111] Further studies need to be conducted to show a stronger relationship between these areas of brain involvement with common results of yoga and meditation, (improved mental health and well-being).

One reason that mindfulness-based approaches could have the impact of decreased anxiety is a result of a decrease in activity with the amygdala, the area of the brain that is involved with the "fight or flight" response.[112] Another reason this treatment assists anxious individuals is its ability to reduce cortisol levels. This occurs as levels of glucocorticoids remain elevated and act as a force of resistance against cortisol.[112]

Biological Impact

Mindfulness-based stress reduction has been found to interact and regulate physiological factors such immune, metabolic, cardiovascular, and endocrine systems.[112]

Meditation has been shown to change grey matter concentrations and the precuneus.[113][41][114][42][40]

An eight-week MBSR course induced changes in gray matter concentrations.[41] Exploratory whole brain analyses identified significant increases in gray matter concentration in the PCC, TPJ, and the cerebellum. These results suggest that participation in MBSR is associated with changes in gray matter concentration in brain regions involved in learning and memory processes, emotion regulation, self-referential processing, and perspective taking. Studies have found that regular meditation practice increases the protein BDNF in the brain and improves cellular health, reduces the rate of aging within cells, and a reduction of grey matter decay in the brain making it possible for higher neuroplasticity over longer periods of time.[115] Meditation has been linked to higher levels of cognitive flexibility and a greater ability to recognize cognitive evaluations and functions.[116] Recent studies suggest that meditation can increase the amount of gray matter in the medulla oblongata located in the brain stem leading to decreased arousal when dealing with unpleasant situations and higher levels of activity in the higher cortical regions of the brain and insula.[108] Meditation has shown to increase activity in anterior cingulate cortex (ACC) and enhance communication from the anterior cingulate cortex to the rest of the brain resulting in a better ability to evaluate and resolve cognitive tasks.[117] Studies have shown that meditation actually increases the amount of white matter within the parts of the brain that assist in self regulation and behavior.[117]

Meditation has been found to decrease mind wandering and allows the brain to fully focus on challenging tasks for longer periods of time without getting distracted. This is due to an increased ability to reduce activity in the default mode network when focusing on a particular task.[118] Non directive forms of meditation where the meditator lets their mind wander freely can actually produce higher levels of activity in the default mode network when compared to a resting state or having the brain in a neutral place.[118][119] These Non directive forms of meditation allows the meditators to have better control over thoughts during everyday activities or when focusing on specific task due to a reduced frustration at the brains mind wandering process.[119] When given a specific task, meditation can allow quicker response to changing environmental stimuli. Meditation can allow the brain to decrease attention to unwanted responses of irrelevant environmental stimuli and a reduces the Stroop effect. Those who meditate have regularly demonstrated more control on what they focus their attention on while maintaining a mindful awareness on what is around them.[120]  Experienced meditators have been shown to have an increased ability when it comes to conflict monitoring[18] and find it easier to switch between competing stimuli.[121] Those who practice meditation experience an increase of attentional resources in the brain and steady meditation practice can lead to the reduction of the attentional blink due to a decreased mental exertion when identifying important stimuli.[121]

Studies have shown that meditation has both short-term and long-term effects on various perceptual faculties. In 1984 a study showed that meditators have a significantly lower detection threshold for light stimuli of short duration.[122] In 2000 a study of the perception of visual illusions by zen masters, novice meditators, and non-meditators showed statistically significant effects found for the Poggendorff Illusion but not for the Müller-Lyer Illusion. The zen masters experienced a statistically significant reduction in initial illusion (measured as error in millimeters) and a lower decrement in illusion for subsequent trials.[123] Tloczynski has described the theory of mechanism behind the changes in perception that accompany mindfulness meditation thus: "A person who meditates consequently perceives objects more as directly experienced stimuli and less as concepts… With the removal or minimization of cognitive stimuli and generally increasing awareness, meditation can therefore influence both the quality (accuracy) and quantity (detection) of perception."[123] Brown also points to this as a possible explanation of the phenomenon: "[the higher rate of detection of single light flashes] involves quieting some of the higher mental processes which normally obstruct the perception of subtle events." In other words, the practice may temporarily or permanently alter some of the top-down processing involved in filtering subtle events usually deemed noise by the perceptual filters.

Meditation enhances memory capacity specifically in the working memory and increases executive functioning by helping participants better understand what is happening moment for moment. Those who meditate regularly have demonstrated the ability to better process and distinguish important information from the working memory and store it into long-term memory with more accuracy than those who do not practice meditation techniques.[109] Meditation may be able to expand the amount of information that can be held with in working memory and by so doing is able to improve IQ scores and increase individual intelligence.[118] The encoding process for both audio and visual information has been shown to be more accurate and detailed when meditation is used.[121] Though there are limited studies on meditation's effects on long-term memory because of meditations ability to increase attentional awareness episodic long-term memory is believed to be more vivid and accurate for those who meditate regularly. Meditation has also shown to decrease memory complaints from those who suffer with Alzheimers disease which also suggests the benefits meditation could have on episodic long-term memory which is linked to Alzheimers.[124]

According to an article in Psychological Bulletin, EEG activity slows as a result of meditation.[125] The National Institutes of Health (NIH) has written, "It is thought that some types of meditation might work by reducing activity in the sympathetic nervous system and increasing activity in the parasympathetic nervous system," or equivalently, that meditation produces a reduction in arousal and increase in relaxation.

Herbert Benson, founder of the Mind-Body Medical Institute, which is affiliated with Harvard University and several Boston hospitals, reports that meditation induces a host of biochemical and physical changes in the body collectively referred to as the "relaxation response".[126] The relaxation response includes changes in metabolism, heart rate, respiration, blood pressure and brain chemistry. Benson and his team have also done clinical studies at Buddhist monasteries in the Himalayan Mountains.[127] Benson wrote The Relaxation Response to document the benefits of meditation, which in 1975 were not yet widely known.[128]

Although the most common modern characterization of Buddhist meditation is a 'relaxation' technique, both scientific studies and Buddhist textual sources proves meditation's arousing or wake-promoting effects.[129] Meditations aiming at improving meta-cognitive skills and compassion (e.g. loving-kindness meditation) are associated with physiological arousal, compared to breathing meditation.[130] Theravada (i.e.Vipassana) styles of meditation induce relaxation responses, while Vajrayana styles of meditation induce arousal responses.[131] Short term meditation training enables the voluntary activation of the Sympathetic Nervous System (SNS) results in epinephrine release.[132] When the SNS is activated, human body is turning into 'fight or flight' mode, whereas the PNS is termed the 'rest and digest' mode.[133] For example, when SNS is activated, heart rate, blood pressure, and respiration will be increased, and catecholamines will be produced, while heart rate variability and galvanic skin resistance will be decreased.[133] Therefore, Relaxing meditation seems to correspond to PNS dominance, and arousing meditation seems to correspond to SNS dominance.

Aging is a process accompanied by a decrease in brain weight and volume. This phenomenon can be explained by structural changes in the brain, namely, a loss of grey matter. Some studies over the last decade have implicated meditation as a protective factor against normal age-related brain atrophy.[134] The first direct evidence for this link emerged from a study investigating changes in the cortical thickness of meditators. The researchers found that regular meditation practice was able to reduce age-related thinning of the frontal cortex, though these findings were restricted to particular regions of the brain.[135] A similar study looked to further expand on this finding by including a behavioural component. Consistent with the previous study, meditators did not show the expected negative correlation between grey matter volume and age. In addition, the results for meditators on the behavioural test, measuring attentional performance, were comparable across all age groups.[136] This implies that meditation can potentially protect against age-related grey matter loss and age-related cognitive decline. Since then, more research has supported the notion that meditation serves as a neuroprotective factor that slows age-related brain atrophy.[134][137] Still, all studies have been cross sectional in design. Furthermore, these results merely describe associations and do not make causal inferences.[138] Further work using longitudinal and experimental designs may help solidify the causal link between meditation and grey matter loss. Since few studies have investigated this direct link, however insightful they may be, there is not sufficient evidence for a conclusive answer.

Research has also been conducted on the malleable determinants of cellular aging in an effort to understand human longevity. Researchers have stated, "We have reviewed data linking stress arousal and oxidative stress to telomere shortness. Meditative practices appear to improve the endocrine balance toward positive arousal (high DHEA, lower cortisol) and decrease oxidative stress. Thus, meditation practices may promote mitotic cell longevity both through decreasing stress hormones and oxidative stress and increasing hormones that may protect the telomere."[139][140]

Studies have shown meditators to have higher happiness than control groups, although this may be due to non-specific factors such as meditators having better general self-care.[141][142][96][95]

Positive relationships have been found between the volume of gray matter in the right precuneus area of the brain and both meditation and the subject's subjective happiness score.[143][113][41][114][42][40] A recent study found that participants who engaged in a body-scan meditation for about 20 minutes self-reported higher levels of happiness and decrease in anxiety compared to participants who just rested during the 20-minute time-span. These results suggest that an increase in awareness of one's body through meditation causes a state of selflessness and a feeling of connectedness. This result then leads to reports of positive emotions.[144]

A technique known as Mindfulness-Based Stress Reduction (MBSR) displays significant benefits for mental health and coping behaviors. Participants who had no prior experience with MBSR reported a significant increase in happiness after 8 weeks of MBSR practice. Focus on the present moment and increased awareness of one's thoughts can help monitor and reduce judgment or negative thoughts, causing a report of higher emotional well-being.[145] The MBSR program and evidence for its effectiveness is described in Jon Kabat-Zinn's book Full Catastrophe Living.[146]

The following is an official statement from the US government-run National Center for Complementary and Integrative Health:

"Meditation is considered to be safe for healthy people. There have been rare reports that meditation could cause or worsen symptoms in people who have certain psychiatric problems, but this question has not been fully researched. People with physical limitations may not be able to participate in certain meditative practices involving physical movement. Individuals with existing mental or physical health conditions should speak with their health care providers prior to starting a meditative practice and make their meditation instructor aware of their condition."[147]

Adverse effects have been reported,[148][149] and may, in some cases, be the result of "improper use of meditation".[150] The NIH advises prospective meditators to "ask about the training and experience of the meditation instructor… [they] are considering."[147]

As with any practice, meditation may also be used to avoid facing ongoing problems or emerging crises in the meditator's life. In such situations, it may instead be helpful to apply mindful attitudes acquired in meditation while actively engaging with current problems.[151][152] According to the NIH, meditation should not be used as a replacement for conventional health care or as a reason to postpone seeing a doctor.[147]

Meditation has been show to reduce pain perception.[153] An intervention known as mindfulness-based pain management (MBPM) has been subject to a range of studies demonstrating its effectiveness.[154][155]