Meta-analysis of the Effect of Yogic Techniques on Melatonin Levels: Implications for Sleep Health

Abstract

Yoga has gained attention as a potential intervention for improving various aspects of health, including sleep quality. Melatonin, a hormone involved in regulating the sleep–wake cycle, has been suggested to play a key role in mediating the effects of yoga on sleep. However, the impact of yoga on melatonin levels remains unclear. The current meta-analysis aimed to evaluate the effect of yoga on melatonin levels based on existing studies. A systematic literature search was conducted to identify studies investigating the impact of yoga on melatonin levels. Five eligible studies were included, comprising a total of 196 observations. The standardized mean difference (SMD) was calculated as the effect size measure. The current meta-analysis was performed using a random-effects model to estimate the pooled SMD, along with 95% confidence intervals (CIs) in R software (version 4.3.2). Heterogeneity across studies was assessed using the I² statistics. Totally five studies were included in the current meta-analysis. The meta-analysis revealed a moderate certainty of evidence on the role of yogic techniques on melatonin levels, with a pooled SMD of 0.37 (95% – CI: [0.09; 0.66]). This meta-analysis provides evidence supporting the regular practice of yoga, including meditation and mantra chanting, in enhancing the melatonin levels. This increase in melatonin may contribute to improved sleep quality. These results underscore the potential of yoga as a nonpharmacological approach for enhancing sleep health and overall well-being. Further research is needed to elucidate the underlying mechanisms and optimal practices for incorporating yoga into sleep management strategies.

Introduction

Yoga, an ancient practice originating from India, encompasses physical postures, breath control, meditation, and philosophical principles aimed at achieving harmony between the body and mind.[1] Over the years, yoga has gained popularity worldwide as a holistic approach to promoting health and well-being.[2] In addition to its well-documented benefits for physical fitness and stress reduction, yoga has been increasingly recognized for its potential therapeutic effects on sleep quality.[3] Sleep is essential for overall health and functioning, yet many individuals experience disturbances in sleep patterns, ranging from difficulty falling asleep to frequent awakenings during the night.[4] Poor sleep quality not only impairs daytime functioning but also increases the risk of various health problems, including cardiovascular disease, obesity, and mental health disorders.[5] Consequently, there is growing interest in identifying effective interventions for improving sleep quality, particularly nonpharmacological approaches that minimize the potential for adverse side effects.[6,7]

Melatonin, often referred to as the “sleep hormone,” plays a crucial role in regulating the sleep–wake cycle[8] secreted by the pineal gland in response to darkness, melatonin helps synchronize the body’s internal clock and promotes the onset of sleep.[9] Given its role in sleep regulation, melatonin has been a target for interventions aimed at improving sleep quality. Several studies have suggested that yoga may influence melatonin levels; however, the findings have been inconsistent.[10]

While some studies have reported increases in melatonin levels following yoga practice, others have found no significant changes or even decreases.[11] The variability in findings may be attributed to differences in study designs, participant characteristics, yoga interventions, and methods of assessing melatonin levels. To clarify the impact of yoga on melatonin levels, a comprehensive synthesis of existing evidence is warranted.

Therefore, the current systematic review and meta-analysis aimed to evaluate the effect of yoga on melatonin levels by synthesizing data from published studies. By providing a quantitative summary of the available evidence, the current study seeks to elucidate the potential of yoga as a nonpharmacological intervention for enhancing sleep quality through its effects on melatonin levels.

Methods

The current systematic review and meta-analysis was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The current review protocol was registered in the International Prospective Register for Systematic Reviews (PROSPERO) under the registration number CRD42024544791 (Available from: https://www.crd.york.ac.uk/PROSPERO/view/CRD42024544791).

Literature search strategy

A systematic literature search was conducted to identify relevant studies examining the impact of yoga on melatonin levels. Electronic databases, including PubMed/Medline, Scopus, PsycINFO, and the Cochrane Library, were searched from inception to April 2024. The search strategy included combinations of keywords related to yoga (“yoga,” “yogic,” “yogic practices”) and melatonin (“melatonin,” “sleep hormone,” “pineal gland”). In addition, reference lists of the relevant articles and reviews were manually screened to identify the additional studies.

Study selection criteria

Inclusion criteria

All the articles entitled as original research papers published in peer-reviewed journals were taken. Studies that investigated the effects of yoga practice on melatonin levels, on human participants of any age or health status with results that reported quantitative data on melatonin levels before and after yoga intervention or compared melatonin levels between yoga practitioners and nonpractitioners written in English language were included.

Exclusion criteria

Studies that integrated yoga with other treatment modalities, such as pharmacological interventions, physiotherapy, or structured exercise programs, were excluded. To ensure a clear distinction, only studies where yogic techniques (asanas, meditation, and pranayama) were the sole intervention were considered.

Data extraction

Two independent reviewers (SV and YV) screened the titles and abstracts of the identified articles to determine their eligibility for full-text review. Any discrepancies were resolved through discussion and consensus with a third reviewer (SY). Full-text articles that met the inclusion criteria were retrieved and assessed for data extraction.

The following information was extracted from each study: author (s), publication year, study design, participant characteristics (e.g., age, sex, and health status), details of the yoga intervention (e.g., type of yoga, duration, and frequency), methods used to assess melatonin levels, and quantitative data on melatonin levels before and after the yoga intervention. The data extraction process was conducted systematically. In cases where the studies had missing data, such as absent standard deviations (SDs), appropriate statistical methods were applied. When possible, missing data were imputed using established guidelines (e.g., estimating SDs from confidence intervals (CIs) or interquartile ranges). However, if essential data could not be obtained or reliably estimated, the study was excluded from the meta-analysis.

Quality assessment

The methodological quality of the included studies was evaluated using the Newcastle–Ottawa Scale (NOS) for nonrandomized controlled trials (RCTs) and the Cochrane risk of bias tool for RCTs. The NOS assesses the quality of nonrandomized studies based on selection, comparability, and outcome criteria, with a maximum score of 9 points indicating the highest quality. For RCTs, domains such as random sequence generation, allocation concealment, blinding of participants and personnel, incomplete outcome data, selective reporting, and other biases were assessed.

Data synthesis and analysis

The primary outcome measure was the change in melatonin levels following yoga intervention, expressed as the standardized mean difference (SMD) between pre- and postintervention values. When available, data on mean melatonin levels and SDs were extracted for both pre- and postintervention time points. If SDs were not reported, they were calculated from standard errors, CIs, or other available data. Meta-analysis was performed using a random-effects model to estimate the pooled SMD and 95% CIs in R software (version 4.3.2; R Foundation for Statistical Computing, Vienna, Austria). Heterogeneity across studies was assessed using the I² statistic and the Q test. Subgroup analyses based on the type of study (RCT vs. non-RCT) were conducted. The certainty of evidence was assessed by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach using GRADEPro.

Results

Literature selection

The systematic literature search yielded a total of 30 articles after removing duplicates. Following title and abstract screening five articles that met the inclusion criteria were selected for full-text review and were included in the qualitative synthesis. After assessing the full-text articles, five studies were deemed eligible for the meta-analysis [Figure 1].

Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram

Basic characteristics of the included studies

Five studies were included in the current meta-analysis. The main characteristics of the included studies are shown in Table 1. Both RCTs[12,13] and non-RCTs[14,15,16] were included in the study, all of which were published in English between 2000 and 2023. Among the five studies, one was conducted in Australia,[12] one in India,[13] one in Norway,[14] one in Taiwan,[15] and one in Sri Lanka.[16] The age of the participants ranged from 18 to 70 years. The sample sizes varied, with the largest being 58 participants and the smallest being 14. Of the five studies, four utilized only meditation as the intervention,[12,14,15,16] while one study incorporated yogic asanas, pranayama, and meditation.[13] Melatonin levels were measured in participants who practiced meditation for durations ranging from 30 min to 3 years. The outcome measures were assessed using radioimmunoassay. Plasma samples were used in three studies,[12,13,14] a saliva sample was used in the study by Thambyrajah et al.,[15] and a serum sample was used in the study by Solberg et al.[16] to evaluate melatonin levels.

Table 1.

The main details of the included studies

Author (year)	Country	Age (years)	Sample size	Study design	Intervention for the experimental group	Intervention for the control group	Outcome measurements	Result
Tooley et al. (2000)[12]	Australia	Mean age 38.82	Total=14 meditators, Experimental group=7 Control group=7	RCT	Meditation for 30 min at one night	Quiet sitting	Plasma melatonin levels were assayed using a radioimmunoassay	Meditation affect plasma melatonin levels
Harinath et al. (2004)[13]	India	25–35	Total=30 healthy men Experimental group=15 Control group=15	RCT	Yogic asanas (postures) for 45 min and pranayama for 15 min during the morning, whereas during the evening hours these subjects performed preparatory yogic postures for 15 min, pranayama for 15 min, and meditation for 30 min daily, for 3 months	Flexibility exercises, slow running and played games	Circulatory levels of melatonin were estimated in 1 mL of plasma using double-antibody radioimmunoassay based on the Kennaway G280 antimelatonin antibody kits from Buhlmann Labs, Postfach, Switzerland	Yogic practices can be used as psychophysiologic stimuli to increase endogenous secretion of melatonin
Solberg et al. (2004)[16]	Norway	Mean age 46	Total=54 advanced male meditators, Experimental group=26 Control group=28	Non-RCT	Meditation had practiced for 30 min for twice in a day by advanced meditators	Quiet rest	The extract was subjected to melatonin measurement using the Buhlman EIA (Allschwill 1, Switzerland)	The findings suggest that advanced meditators have higher melatonin levels than nonmeditators
Hui Liou et al. (2010)[14]	Taiwan	29–64	Total=40 regular meditators, Experimental group=20 Control group=20	Non-RCT	Chinese original quiet sitting (type of traditional Chinese meditation) was practiced for 90 min for 2 days by advanced meditation practitioners	Quiet rest	Melatonin levels were obtained using saliva collection tubes (Salivette, Sarstedt Inc., Rommelsdorf, Germany) and analyzed with competitive enzyme-linked immunoassay (direct saliva melatonin ELISA kit; Buhlmann Laboratories, Schonenbuch, Switzerland)	Chinese original quiet sitting can be used as a psychophysiological stimulus to increase endogenous secretion of melatonin
Thambyrajah et al. (2023)[15]	Sri Lanka	Above 18	Total=58 long-term meditators Experimental group 29 Control group=29	Comparative cross-sectional study	Long-term Vipassana meditators had practiced meditation at least 1 week cumulatively in formal sessions of meditation (retreat or temple based) and 6 h per week for the last 3 years	The control group received no treatment	Melatonin levels were analyzed in the serum samples using an enzymatic immunoassay kit (Melatonin ELISA, LDN, Nordhorn, Germany)	The findings indicate elevated melatonin levels in the long-term meditators

RCT: Randomized controlled trial, EIA: Enzyme immunoassay, ELISA: Enzyme-linked immunosorbent assay, LDN: Labor diagnostika nord

Risk of bias of the included studies

Two[12,13] of five included studies, which were RCTs, showed some concerns of bias in randomization process, deviation from the intended interventions, and bias in the outcome assessment [Figure 2]. Whereas, three[14,15,16] non-RCTs quality assessed using NOS in selection, comparison, and outcome revealed low risk of bias [Table 2].

Figure 2.

Risk of bias assessment for randomized controlled trials

Table 2.

Risk of bias assessment for nonrandomized controlled trials

Author and year	Selection	Comparability	Outcome	Total	Risk assessment (high <7 or low ≥7)
Solberg, 2004[16]	4	2	2	8	Low
Chien-Hui Liou, 2010[14]	4	2	2	8	Low
Thambyrajah, 2023[15]	4	2	2	8	Low

Meta-analysis of primary outcome

The meta-analysis included the data from five studies with a total of 196 observations, assessing the SMD to evaluate the effect of the intervention. The pooled effect yoga practices on melatonin levels shown in Figure 3. Under the random-effects model, the pooled SMD was 0.37 (95% CI: 0.09–0.66), indicating moderate effect of yogic techniques on the melatonin level. Whereas, subgroup analysis based on the study type showed very low certainty (0.28 [95% CI: 0.31–0.88]) for RCTs and moderate certainty (0.40 [95% CI: 0.08–0.72]) for non-RCTs. Certainty of evidence is shown in Table 3.

Figure 3.

Pooled effect yoga practices on melatonin levels. CI: Confidence interval, SMD: Standardized mean difference, RCT: Randomized controlled trial

Table 3.

Certainty of evidence

Certainty assessment							Number of patients		Effect		Certainty	Importance
Number of studies	Study design	Risk of bias	Inconsistency	Indirectness	Imprecision	Other considerations	Yogic technique	Placebo	Relative (95% CI)	Absolute (95% CI)
Yogic techniques for improving melatonin levels
5	Randomized trialsa	Seriousb	Not serious	Not seriousc	Not serious	None	97	99	-	SMD 0.37 higher (0.09 higher–0.66 higher)	⨁⨁⨁◯ Moderateb,c	Important
Yogic technique for melatonin levels – RCT
2	Randomized trials	Seriousb	Not serious	Seriousd	Seriouse	None	22	22	-	SMD 0.28 SD higher (0.31 lower–0.88 higher)	⨁◯◯◯ Very lowb,d,e	Important
Yogic technique for melatonin levels - Non-RCT
3	Nonrandomized studies	Not serious	Not serious	Serious	Not serious	None	75	77	-	SMD 0.4 higher (0.08 higher–0.72 higher)	⨁⨁⨁◯ Moderate	Important

^aBoth Randomized and non-Randomized controlled trials, ^bBoth the studies were unclear about the randomization process and the assessment of outcomes in included RCTs downgrade one level, ^cInterventions delivered differently in different settings; level downgraded to one level, ^dInterventions applied in different settings and the populations were differed, ^eLow sample size downgraded by one level. CI: Confidence interval; SMD: Standardized mean difference, RCT: Randomized controlled trial

Discussion

The present meta-analysis provides compelling evidence that yoga interventions can significantly increase melatonin levels. The overall pooled evidence (both randomized and nonrandomized studies) indicates moderate certainty of evidence on the role of practicing yogic techniques on melatonin secretion. However, the pooled effects of RCTs showed that the evidence is very uncertain about the effects of yogic techniques on melatonin levels. Whereas, the pooled effects of non-RCTs showed moderate certainty of evidence.

Previous studies have investigated the effects of yoga on sleep using various markers and scales[17] such as the Pittsburgh Sleep Quality Index, Insomnia Severity Index, total sleep time, sleep onset latency, and sleep efficiency. However, the current study is the first meta-analysis to aggregate findings on the effect of yoga on sleep with melatonin as the primary biomarker, revealing a positive outcome with minimal heterogeneity.

Melatonin, a hormone primarily synthesized by the pineal gland, plays a crucial role in regulating circadian rhythms and promoting sleep onset and maintenance.[10] The increase in melatonin levels observed in this meta-analysis suggests that yoga may modulate the body’s endocrine system, leading to enhanced melatonin production or altered secretion patterns. This effect could potentially contribute to the sleep-promoting benefits of yoga reported in various studies.[7,18]

Several potential mechanisms may explain the relationship between yoga and melatonin levels. Yoga practice involves physical postures (asanas), breathing exercises (pranayama), and meditation techniques, which collectively induce a state of relaxation and reduce stress levels.[17,19] Chronic stress has been associated with dysregulation of the hypothalamic–pituitary–adrenal axis and altered melatonin secretion patterns.[20,21] By reducing stress and promoting a more balanced neuroendocrine state, yoga may facilitate the normalization of melatonin levels.

Furthermore, specific yogic practices, such as pranayama and meditation, may directly influence the autonomic nervous system (ANS) and the pineal gland’s function.[22] The pineal gland, which produces melatonin, is regulated by the ANS, and yoga has been shown to promote parasympathetic dominance, potentially enhancing melatonin synthesis and release.[23] While no study has explicitly examined the effects of specific yogic components (asanas, pranayama, and meditation) on melatonin secretion, some evidence suggests that yogic practices help maintain and increase melatonin levels. One proposed mechanism involves reduced hepatic blood flow during meditation, which may slow melatonin metabolism, leading to higher plasma concentrations of the hormone.[24] Studies have shown a positive correlation between higher nighttime melatonin levels after yoga and meditation and improvements in well-being. However, no significant correlation has been found between melatonin levels and indices of cardiorespiratory function, suggesting that the psychological benefits of yoga and meditation may be linked to increased melatonin secretion, rather than direct physiological changes in cardiovascular function.[25]

Serotonin, a key neurotransmitter associated with psychological well-being, may play a role in this process.[15] Increased serotonin levels have been correlated with improvements in mood and relaxation. The increase in melatonin secretion following yoga may be a result of either enhanced pineal gland activity or decreased clearance from circulation. Yogic practices increase serotonin, which in turn may serve as a precursor for melatonin synthesis.[26] The exact mechanism by which meditation increases melatonin remains unclear. However, since melatonin biosynthesis is inhibited by strong light exposure,[27] practicing meditation with closed eyes may contribute to increased melatonin production. In addition, decreased hepatic blood circulation during meditation may slow melatonin metabolism, leading to higher concentrations of melatonin in the bloodstream.[12]

Melatonin levels also depend on its precursor, serotonin, and studies have shown that an increase in serotonin metabolites, such as 5-hydroxyindoleacetic acid, can directly enhance melatonin synthesis.[28] The combined effects of increased serotonin levels and hypothalamic innervation of the pineal gland during meditation may stimulate melatonin production through the serotonin-to-melatonin conversion pathway.[27]

The minimal heterogeneity observed across the included studies suggests that the positive effect of yoga on melatonin levels is consistent across diverse populations and yoga styles. However, it is essential to consider the prediction interval, which indicates the range of expected effects in future studies. The wide prediction interval (−0.20–0.94) highlights the need for further research to better understand the potential variability in the magnitude of the effect, as well as the factors that may influence the responsiveness to yoga interventions.

Limitations of the current meta-analysis include the relatively small number of studies and the potential for publication bias, as studies with null or negative results may be less likely to be published. In addition, the included studies varied in their yoga interventions, duration, and participant characteristics, which could contribute to the observed prediction interval.

Given the observed effects, future studies should aim to differentiate the influence of specific yogic practices on melatonin secretion. Subgroup analyses focusing on asanas, pranayama, and meditation individually could provide more targeted insights into the mechanisms underlying yoga’s effect on melatonin and sleep health. Understanding these distinctions would help optimize yoga-based interventions for sleep disorders and circadian rhythm regulation.

Conclusion

The findings of this meta-analysis underscore the potential of yoga as a valuable adjunctive therapy for enhancing sleep health and overall well-being. However, further research is needed to elucidate the optimal practices and mechanisms underlying the observed effects, ultimately informing evidence-based interventions for sleep disorders and promoting better sleep outcomes for individuals worldwide.

Data availability statement

All data generated or analyzed during this study are included in this published article.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.