authored by Rashmi Shiju*
Abstract
Background:b> Yoga is being evaluated for its potential beneficial effect on people with type 2 diabetes(T2DM) as an adjuvant therapy by researchers around the globe. Few systematic reviews and meta-analyses previously performed have indicated mixed effect of yoga. In this review we aimed to evaluate further whether yoga has an impact on metabolic parameters in people with T2DM.
Methods: Systematic review and meta-analysis of randomized controlled trials (RCTs) comparing the practice of any type of yoga, asanas or pranayamas vs. standard care in adults with T2DM. The primary outcome was change in fasting plasma glucose and glycated haemoglobin (HbA1c). The secondary outcome was serum lipid profile and oxidative stress. The electronic databases such as, Cochrane CENTRAL, Scopus, Medline, Embase and CINAHL were searched from the year 1990 to August 2015 to find out the studies done on yoga as per the eligibility criteria. Meta-analysis was conducted using the inverse variance method of analysis with random-effect models with checks of heterogeneity using the I2 test.
Results:b> From a total of 788 articles screened, nine RCTs were included involving 788 participants. In five trials yoga group had a significant reduction in HbA1c ( mean difference(MD) -0.51% , 95%CI -0.57 to -0.44, P =0.006, fasting plasma glucose (mean difference(MD) as -25.2 ,95 % CI -25.31 to -25.2mg/dl, P <0.00001, and serum LDL (mean difference(MD) -26.8mg/dl , 95% CI -42.1 to -11.5 mg/dl, p =0.0006), HDL (mean difference(MD) 6.8 mg/dl (95% CI 4.8 to 8.7, p <0.00001), total cholesterol (mean difference(MD) -33.3 mg/dl (95% CI -35.8 to -30.8, p <0.00001), triglycerides (mean difference(MD) 39.4 mg/dl( 95% CI -50.0 to -28.8, p <0.00001), cortisol (mean difference(MD) -5.5 μg /l ( 95% CI -7.1 to -4.0, p <0.00001), malondialdehyde (mean difference(MD) 16.6 nanomol/dl (95%CI -22.0 to -11.2, p<0.00001).
Conclusion:The results from the available trials indicate that yoga may be a potentially beneficial intervention for improving glycemic control, lipid profile and indicators of oxidative stress in people with T2DM. Further studies are required to corroborate yoga’s effect on other outcomes such as psychosocial profiles.
Keywords: Yoga; Systematic review; Meta-analysis; T2DM; Stress
Abbreviations: BMI: Body Mass Index; CAM: Complementary and Alternative Medicine; FBG: Fasting Blood Glucose; HDL: High Density Lipoprotein; LDL: Low Density Lipoprotein; MENA: Middle East and North Africa; MDA: Malondialdehyde; RCT: Randomized Controlled Trials; T2DM: Type 2 Diabetes Mellitus
Introduction
Diabetes mellitus is a progressive disease affecting large numbers of the people globally. According to the International Diabetes Federation (IDF) Atlas 9th edition, globally 463 million adults are affected with diabetes, and is estimated to rise to 700 million by 2045 without intervention [1]. Managing diabetes can be challenging and requires a multifaceted approach involving lifestyle changes and pharmacological intervention. People with diabetes do not infrequently use complementary and alternative medicine (CAM) with estimates ranging from 17% and 73% and involved lifestyle modification, yoga, qi gong, massage and herbs [2]. Yoga is the most common alternative holistic approach adopted by adults in many countries. According to national survey in the US, yoga use increased from 9.5% to 14.3% between 2012 and 2017 [3]. Yoga originated from India has been a traditional contemplative practice since time immemorial for the therapeutic intervention and health maintenance [4]. Yoga may be beneficial in almost all the ailments. [5-11]. It may have positive impact on endocrine system, nervous system, circulatory system, metabolism, psychology and cognition [12]. Yoga has also been shown to influence hormone regulation and studies suggest that regular practice of yoga can reduce cortisol and sympathetic activation while increasing serotonin, gaba aminobutyric acid (GABA) and oxytocin levels. [5,7,13,14]. This may in turn reduce anxiety, depression, perceived stress and improving sleep quality and male sexual functioning [15]. Yoga may have beneficial effect in people with T2DM, in terms of modifiable risk factors and metabolic syndrome [16-24]. The systematic review by Innes et al. [25] measured the influence of yoga-based programs on risk profiles in adults with type 2 diabetes. The review indicated that yoga may help in reducing the risk in adults with T2DM. The author also indicated that there are limited reviews to show the promising effect of yoga on psychological profiles in adults with diabetes. The systematic analysis by AlJasir et al. [26] showed that short-term benefit can be achieved by T2DM patient with the practice of yoga were however inconclusive and non-significant for the long-term outcomes of yoga practice. A systematic review and meta-analysis by Harpreet et al. [27] indicated that yoga participants successfully improved their glycated haemoglobin (HbA1c) as compared with the control people. Yoga also had significant improvements in lipid profiles, blood pressure, body mass index (BMI), waist/hip ratio and cortisol levels. A systematic review by Divya et al. [28] on effects of yoga on physical health and health related quality of life concluded that there were significant improvements in physical health and quality of life. In another systematic review and meta-analysis by Ramamoorthi et al. [29] reported significant improvements of yoga on glycaemic control, serum lipid profiles and other parameters in prediabetic populations. The present systematic review and meta-analysis will focus on patients with T2DM conducted through randomized controlled trials (RCTs) with yoga intervention such as Sudarshan kriya yoga, asanas, pranayamas and hatha yoga with duration at least four weeks. This review will give more focus to specific type of yoga intervention and its effect on glycaemic control, serum lipids and stress biomarkers. To our knowledge, this will be the first meta-analysis on oxidative stress markers.
Methods
Study selection criteria and PICOS
Cochrane review guidance was followed in conducting the systematic review [30].
Population for this systematic review was defined as:b> Adult patients aged 18 years or greater having T2DM for more than one year confirmed by a physician based on the guidelines for diagnosis of T2DM. Exclusion criteria included ;studies on infants and children, gestational diabetes, pregnant women, non-diabetic patients, type 1 diabetic patients, complication of diabetes and studies with herbal drug intervention.
The intervention included:b> any type of yoga (hatha, bikram, iyengar, sudarshan kriya yoga, pranayama, astanga, asanas), and minimum four week of duration of yoga. Comparison was control groups receiving standard treatment of care.
Outcomes:b> The primary outcomes were changes in fasting plasma glucose (FPG) and HbA1c. Secondary outcomes included changes in serum high density lipoprotein (HDl), low density lipoprotein (LDL) and total cholesterol, BMI, stress biomarkers and quality of life.
Study design: Only randomized clinical trial was selected for inclusion.
Database search strategy
The search strategy was implemented in ; Pubmed, Embase, Scopus, Cochrane, Medline, CINAHL Plus were searched using the key words “Yoga OR asana* OR Bikram OR Iyengar OR pranayama OR hatha OR ashtanga OR Sudarshan Kriya Yoga AND diabetes OR diabet* OR non-insulin dependent OR diabetes mellitus OR T2 DM OR Type II diabetes mellitus”. Apart from the database, the bibliography of the articles selected were also searched. Limits applied were for age greater than 18, articles published from 1990 to 2015, English language. Moreover, an internet searching was done through Google Scholar and also clinical trial.gov website for randomized controlled trials. Literature on systematic reviews and metaanalysis of yoga and diabetes published until 2019 were included.
The results obtained from searching each electronic database using the above-mentioned key words were saved in the computer and online End Note in order to keep a track of all searches which included number of hits, database name, time period searched, limitations applied. The results of search from each database also exported to Excel to sort out duplication and based on the eligibility criteria of systematic review.
Data extraction and screening
All the six databases were searched with key words mentioned and then screened for duplicates. The title and the abstract were screened for relevance. Full text articles were then scanned according to the eligibility criteria. The details of the number of articles excluded with reason are depicted in the flow chart (Figure 1). The results obtained from the database were extracted using the extraction form (Appendix I).
Quality assessment
A short scale of seven criteria customized to yoga studies were used to assess the quality of the included studies established by the Cochrane collaboration [30].
Following questions were included in the quality checklist:
• Whether participants were randomized to groups randomly or through software or independantly.
• Were the baseline characteristics of the study groups properly assessed or there was any correction done to balance.
• Whether the study has calculated sample size through power analysis.
• Whether the study has considered loss of follow up, attrition.
• Whether the study had properly handled the missing data by using intention-to-treat analysis,
• Study integrity; was the study followed as planned.
• Whether the study was conducted with certified progessional yoga instructor or not. Each criterion was rated as 0(study does not meet criteria) or 1 (study met criteria).
When a criterion meets six or seven points then the study is assessed as high quality and when four or five criteria were mint then assessed as low and very low when zero or one criteria were met. Data collected were assessed for the quality of studies based on the quality criteria. If a trial meets first three criteria, then it is categorized as low risk of bias. (Table 1).
Data Analysis
Meta-analysis of the eligible studies was conducted using statistical RevMan software measuring the mean differences using the generic inverse variance method of analysis. Meta-analysis was performed for HbA1c reported as a percentage and FPG reported as mg/dl. When the units for reported values of FPG in the articles differed, the units were Mmol/L they were converted into mg/ dl by multiplying the mmol/L value by 18. The generic inversevariance method of analysis was used to pool all mean differences for continuous data and for combining intervention effect estimates reporting results from fixed-effect and random-effects models. Statistical heterogeneity was assessed using the I-squared statistic. Mean difference was calculated for the yoga group and the control group. Standard deviation was also extracted from the reviewed articles. Standard errors were converted to standard deviation were appropriate.
Results
Characteristics of the studies
1201 titles and abstract were identified and, nine trials met the eligibility criteria that included 788 participants. Characteristics of included trials depicted in Table 2. Four trials (44.4%) reported HbA1C as primary outcome. Seven trials reported FPG an outcome but only one trial (11.1%) reported serum cholesterol, LDL, HDL triglycerides as an outcome. Two trials (22.2%) reported quality of life as an outcome. Most trials (55.6%) practiced three months of yoga as an intervention whilst this ranged from eight weeks to nine months in the remaining trials. The duration of each yoga class also varied between the trials from one and two hours.
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