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Year : 2019  |  Volume : 12  |  Issue : 2  |  Page : 162-171
Evidence base of yoga studies on cardiovascular health: A bibliometric analysis


Division of Yoga and Life Sciences, S-VYASA Deemed University, Bengaluru, Karnataka, India

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Date of Web Publication6-May-2019
 

   Abstract 


Noncommunicable diseases including coronary artery disease contribute to approximately 50% of global mortality. Pharmacological treatment alone may not be a panacea for such diseases since it may be associated with various other adverse effects. Hence, strategies such as Yoga involving healthy lifestyle and stress management are widely sought by the patient population. Materials and Methods: An electronic search of PubMed as a standard bibliographic database was performed through February 2015 using the keywords “Yoga” and “Cardiovascular.” Studies with Yoga as the independent variable and parameters related to cardiac health as the dependent variable were included and exclusion criteria were applied. Results: A total of 149 publications were identified which met the inclusion criteria for analysis. Of the total publications, 44% were clinical trials of which 19% were randomized controlled trials which may be categorized as high-quality ones. An upward trend in the overall research in this area is evident. Major work has been accomplished by researchers of the United States (38%) and India (29%). Conclusion: The survey indicates that the number of publications in the field of “Yoga” and “Cardiovascular” health has increased rapidly in the late years. Analysis comprising the nation/state helps define its status with regard to its counterparts and helps understand science priorities and disease control strategies in an effort to provide cost-effectiveness and quality control. There is a need for further high-quality studies in the field of “Yoga” and “Cardiovascular” diseases to validate the effects of Yoga on health parameters.

Keywords: Bibliometrics, cardiovascular, yoga

How to cite this article:
Srihari Sharma K N, Choudhary NR, Subramanya P. Evidence base of yoga studies on cardiovascular health: A bibliometric analysis. Int J Yoga 2019;12:162-71

How to cite this URL:
Srihari Sharma K N, Choudhary NR, Subramanya P. Evidence base of yoga studies on cardiovascular health: A bibliometric analysis. Int J Yoga [serial online] 2019 [cited 2019 May 27];12:162-71. Available from: http://www.ijoy.org.in/text.asp?2019/12/2/162/257631



   Introduction Top


Noncommunicable diseases such as coronary artery disease (CAD), cancer, diabetes, and chronic obstructive pulmonary disease put together contribute to 50% of global mortality. Of these, cardiovascular disease (CVD) is known to be the number one cause of death and disability worldwide (WHO 2011). Around 29.6% of total global deaths can be attributed to CVD (WHO 2003). It is estimated that by 2030, CVDs will account for almost 23.6 million deaths (WHO 2011).[1],[2] Several risk factors such as smoking, high-fat diet, sedentary lifestyle, and psychological factors, including stress, depression, and hostility contribute to coronary heart disease.[3] The pharmacological treatment used for treating CVD has limited efficacy along with various adverse effects. Therefore, there is an upsurge in patients opting for other strategies for healthy lifestyle and stress management in an attempt to improve health-related quality of life and to prevent recurrent illness. Yoga is the alternative strategy patients prefer since it involves both stress management and exercise. It is one of the most popular complementary and alternative medicine (CAM) practices, incorporating Asanas (postures), Pranayama (breathing exercises), Dhyana (meditation), and certain philosophical principles to create a sense of well-being.[4],[5]

More recently, its therapeutic aspect has been validated in a range of medical conditions such as psychopathological, cardiovascular, respiratory, and metabolic diseases. Under the broad umbrella of CAM, Yoga therapy is being recognized worldwide as an alternative approach to many health-related issues.[6] A general feature of these practices is their capability of inducing psychophysiological balance. It is postulated that Yoga practice improves CVD-related outcome through following two pathways, vagal stimulation and parasympathetic activation as shown in [Figure 1].[7] Yoga's therapeutic potential in the field of cardiovascular health has been explored in a growing number of trials to date although consolidation of evidence as bibliometric analysis is limited. Hence, the purpose of the present study is to provide a comprehensive review of available research evidence in the field of cardiovascular health through a bibliometric analysis.
Figure 1: Flowchart of the yoga intervention pathway. The full form of abbreviations is as follows: HPA = Hypothalamic pituitary adrenal and CVD = Cardiovascular disease

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   Materials and Methods Top


Data source

An electronic search of PubMed as a standard bibliographic database was performed through February 2015 using the keywords “Yoga” and “Cardiovascular.” Studies with Yoga as the independent variable and parameters related to cardiac health as the dependent variable were included and exclusion criteria were applied [Figure 2].
Figure 2: Flowchart depicting study selection

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Study selection

The search strategy was built basically by inputting the keywords “Yoga” and “Cardiovascular.” The country of origin of the article was identified by the first author's country. After removal of duplicate records, identified abstracts were screened independently by two review authors (SSKN and CNR) to determine whether they actually met the eligibility criteria.

Selection criteria

The following selection criteria were applied to include or exclude the studies:

Types of studies

Each study was evaluated as to the presence of a control group and whether participants were randomized to different study arms, to yield three possible study categories: noncontrolled trials, controlled trials, and randomized controlled trials (RCTs). Dissertations, reports or proceedings of meetings, book chapters, articles in foreign language, and those not matching with the keywords, i.e. non-Yoga intervention as well as noncardiovascular outcomes were excluded. Reports or research letters in journals, publications of case reports, and population survey studies and articles with minimum literature availability which were insufficient to categorize have not been included. Although the reviews, meta-analysis, bibliometric analysis, Cochrane reviews, and pilot studies have not been included for analysis, they have been reported in the overall review with respect to the year of publication and place of the origin.

Types of participants

Studies of all types of participants were eligible. No restrictions were applied regarding sociodemographic characteristics, age, and gender or health status.

Types of interventions

Studies were eligible if they assessed the effects of Yoga interventions. Studies were selected irrespective of the tradition, length, frequency, or duration of the Yoga practice. There was no restrict on the inclusion of precise practices provided, the stated practice had a theoretical historical past in Yoga or has been in Yoga practice traditionally. Intervention components such as Asanas (Yoga postures), Pranayama (Yoga breathing techniques), and Dhyana (meditation) were included along with educational sessions on the philosophy of Yoga, Yogic diet, and/or Yogic lifestyle. Studies involving individual co-interventions along with the intervention that was formally studied were included, but those with multimodal interventions were not. No restrictions were applied to control group interventions.

Data extraction

Two authors (SSKN and CNR) independently extracted data using a standardized data extraction form. All relevant data on study design and settings, types of participants, interventions, and outcome measures were extracted and recorded in the data extraction form. We resolved disagreements by consensus or discussion with the third author (SP). The structured data extraction form consisted of the following: (a) publication information (publication year and origin), (b) data on participants (sample size, gender, age, and medical condition), (c) intervention (yoga tradition, program length, intervention components, and control intervention), and (d) outcome measures and conclusion (changes in blood pressure and blood lipids, cardiovascular mortality, myocardial infarction, CABG, stroke, quality of life, and psychological states).

Data analysis

We performed data analysis using SPSS Statistics for Windows, Version 17.0. Chicago: SPSS Inc. Data were presented by counts, percentages, and frequency.


   Results Top


Study characteristics

Of the total of 149 studies, 44% were interventional studies. Among these, the share of RCTs was 19% that of non-RCTs 13% and that of noncontrolled trials were 13%. Next in the hierarchy was occupied by systematic reviews which amounted to 26% of the total studies. Apart from these, 15% of them were one-time studies while another 15% comprised miscellaneous ones, namely, pilot studies, case reports, meta-analysis, surveys, interviews, scientific statements, bibliometric analysis, Cochrane reviews, and letters to the editor, each of which shared a meager percentage. There is an upward trend in the quantum of research work published in this field from the year 1961 onward. There was a minor upsurge compared to the previous couple of decades, with the total number of reaching 17 between the years 1990 and 1999. There was a drastic change in the trend during the subsequent decade, with the number of publications rising up to 59 by the year 2009, with each year consistently contributing to the field of research in this area, the contribution of the year 2007 is the highest at 10 research papers. With a good beginning of 13 publications in the year 2010, the next 5 years saw a tremendous growth in the field of research in “Yoga” and “Cardiovascular” health with the number of research articles published crossing the total number of publications of all the previous years until then reaching the digit “110.” The years 2011 and 2014 were the highest contributors with the number of published articles summing up to 28 and 27, respectively.

The United States (US) (38%) and India (29%) share the majority of research contributions in the field of Yoga and cardiovascular health. This is followed by the United Kingdom, Australia, and Canada with their contributions of 5%, 4%, and 3%, respectively. Others share between 1% and 2% each among the remaining 20% of the publications. The origin of another 4% of the published studies could not be traced.

The randomized controlled trials

RCTs, which are considered the gold standard in experimental studies, were first carried out in this area by the year 1989 for this literature study. It gained momentum by the year 2011 when 25% of all publications in the field were RCTs. This was followed by 18% in 2012, 11% in 2013, and 21% in 2014. India contributed a high of 36% RCTs, followed by the US with 32%, while Australia and Korea share 7% each with only a meager percentage to be shared among UK, Jamaica, Israel, Brazil, and Iran. The trials were conducted on a wide range of populations, including healthy adults, hypertensive participants, diabetics, older adults, heart failure participants, and patients with CAD, and the duration of trial ranged from 8 weeks to 56 weeks, with the majority of the studies incorporating the intervention duration of 12 weeks [Figure 3]. The majority of the studies incorporated the integrated Yoga intervention in combinations of Asanas and Pranayama, and in a few, meditation was also included. The detailed literature review table for the RCTs has been provided in [Table 1].
Figure 3: Yoga duration in weeks. Doughnut chart illustrating the Yoga intervention period in weeks incorporated in different trials. (24% of studies incorporated 8-week duration, 4% incorporated 10 weeks, 41% incorporated 12 weeks, 17% incorporated 16 weeks, 4% incorporated 20 weeks, 4% incorporated 24 weeks, 4% incorporated 32 weeks, and 4% incorporated 56-week duration of yoga practice)

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Table 1: Literature review table for the randomized controlled trials

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The nonrandomized controlled trials

In a span of over 40 years, i.e., between the years 1975 and 2015, we came across 19 non-RCTs. The majority of the trials were from the recent 15 years. Six of the 19 trials originated from the US, while five were from India. Healthy yoga practitioners, hypertensive, and geriatric population predominated the study population apart from sedentary people, smokers, and those infected with HIV [Figure 4]. The duration of the trial ranged from 0 to 48 weeks.
Figure 4: Study population in non-randomized controlled trials. Bar of pie chart illustrating the population recruited for the non- randomized controlled trials. The full form of abbreviations is as follows: HIV = Human immunodeficiency virus

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The single group studies

Nineteen studies fitting into the single group design category were documented post-1997, with 2011 contributing the maximum numbers. Pranayama is the most frequently used Yoga practice, with 10 of 19 studies incorporating this along with, asana, meditation, educational sessions, and yoga-based lifestyle modifications. The duration of trial ranged from 0 to 12 weeks. Blood pressure (12 studies) and heart rate (11 studies) were the most evaluated outcome measures.

The one-time studies

Studies carried out over a single time period were categorized as “one-time” studies. The first such study was documented in the year 1987, and until date, there are 22 such studies in total making up to 15%. India, the US, and Czechoslovakia, respectively, contributed 6 (27%), 5 (23%), and 3 (14%) such studies. Most of the studies have been conducted on Yoga practitioners and healthy population, while a few were for Duchenne muscular dystrophy children, Parkinson's, dementia patients, the sedentary population, as well as runners.


   Discussion Top


This bibliometric analysis reflects a comprehensive review to date of the clinical evidence on Yoga for cardiovascular health, including reviews, RCTs, non-RCTs, case reports, and surveys. Of 149 trials included in the review, only 19% were randomized controlled studies. Most of the trials were short term and conducted on healthy participants. The information gaps in the published literature are highlighted here. There is a lack of reliable, strong evidence on the effects of Yoga on clinical events, blood pressure and lipid levels and for the primary prevention of CVD. There is an increment in the publications in the past one decade; nonetheless, more trials are needed to clarify the potential benefits of Yoga for cardiovascular health. “Previous systematic reviews studied the efficacy of Yoga in the primary and secondary prevention of CVD” (Innes 2005; Jayasinghe 2004). “The majority of the identified studies focused on primary prevention, and only a few identified studies investigated secondary prevention. This may reflect under research on this topic. A population-based study suggested a substantial growth in the use of Yoga as a form of CAM” (Barnes 2008). Nevertheless, the participants exhibit a trend to utilize CAM to treat musculoskeletal problems rather than chronic diseases, namely, lifestyle disorders. The low prevalence of the Yoga might limit exploration of the therapeutic potential of Yoga.

Ugolini et al. in a bibliometric analysis of the fields on the rehabilitation of cerebrovascular and CVDs have come up with similar findings and have reported that the publications in this area increased 8.6 times from the year 1967 to 2008, and after a 20-year period of plateau between 1975 and 1994, there is an addition in the productivity of cardiovascular research in the past 15 years.[8],[9] Major work in this field has been carried out by the researchers from the US and India and the findings of which are consistent with the results of Khalsa in his study on therapeutic Yoga.[10]

Healthy and individuals suffering from hypertension are frequently recruited for the trials. Possibly because the physiological effects of Yoga practice as well as the mechanism of action of a majority of practices are beginning to be clear of late, the trials involving healthy population could help accomplish the task. Yoga is known to inhibit sympathetic activity and facilitate parasympathetic activity. Contrary to conventional exercises, Yoga aims at minimizing oxygen uptake by inducing relaxation. All these practices aim at increasing awareness of the working heart and attempt to reduce heart rate. Therefore, it is commonly adopted by hypertensive individuals as an alternative way to manage such chronic conditions. Blood pressure and heart rate being the direct reflection of autonomic nervous system activity are the commonly used outcome measures followed by lipid profile and aerobic fitness. Moreover, both of these measures are valid, reliable, noninvasive, easily measurable, and cost-effective ones.


   Conclusion Top


The literature survey indicates that the number of publications in the field of “Yoga” and “Cardiovascular” health has increased rapidly in the past few years. The US and India contributed most of the publications. The study further attempts to represent the outcome focusing on Indian states, mainly because India is a major contributor in this field and also since information about this geographical region is sparse. Analysis comprising the nation/state helps define its status about its counterparts and helps understand science priorities and disease control strategies to provide cost-effective and quality control. The literature analysis reveals a deficiency of high-quality studies recruiting patient population in the area of cardiovascular health for Yoga trials. Hence, further high-quality studies investigating the potential effects of Yoga in the management of CVDs may be recommended.

Limitations

The PubMed database was the solitary source of information. Journal publications other than the English language were excluded from the review. Consequently, states with a tradition of bringing out publications in their native languages may be underrated in this recapitulation. The possibility of bias also exists in not considering several unpublished studies in our review. The primary investigators of some identified studies were contacted to obtain additional methodological information to inform our determination as to whether these surveys should be admitted; all the same, most investigators did not respond to our inquiry e-mails. We cannot, therefore, avoid the possibility that we may not have included some eligible studies.

Implications for research

More high-quality RCTs may be recommended to obtain a definitive response to the inquiry of the strength of Yoga for cardiovascular wellness. Emphasis to better methodological quality should be given in the future studies with respect to the design of trials, random sequence generation, group blinding, sample size, sample power, and avoidance of bias in the study to improve the methodological quality. Tests should include relevant issues such as morbidity, composite cardiovascular events, and quality of life. So also, valuation of the cost as well as documentation of cardiovascular-related hospital admissions and untoward results are prescribed. Participants from different ethnic groups and from different countries could be considered as part of a more widespread research. On the basis of the findings of the current study, we advocate an integrated approach toward Yoga incorporating various combinations of asanas, pranayama, kriyas, meditation, and relaxation practices along with lectures and advice on yoga-based lifestyle modifications and diet while addressing the needs of cardiovascular patients. We also recommend an intervention duration of a minimum of 12 weeks for the effects to manifest in such population. Special consideration needs to be given to individual practice as a home program. Biomarker studies which compare Yoga with standard pharmacological and psychotherapies, and studies of long-term efficacy are needed to fully translate the promise of Yoga in the field of cardiac health.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Ajay VS, Gupta R, Panniyammakkal J, Chaturvedi V, Dorairaj Prabhakaran KS. National Cardiovascular Disease Database. Scientific Secretariat of IC Health. New Delhi: Ministry of Health and Family Welfare, Government of India, World Health Organization; 2003.  Back to cited text no. 1
    
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World Health Organization. Prioritizing a preventable epidemic. A primer for the media on noncommunicable diseases; 2011. Available from: http://www.wpro.who.int/noncommunicable_diseases/ncd_primer.pdf. [Last accessed on 2012 Nov 04].  Back to cited text no. 2
    
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Daubenmier JJ, Weidner G, Sumner MD, Mendell N, Merritt-Worden T, Studley J, et al. The contribution of changes in diet, exercise, and stress management to changes in coronary risk in women and men in the multisite cardiac lifestyle intervention program. Ann Behav Med 2007;33:57-68.  Back to cited text no. 3
    
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Krishna BH, Pal P, Pal G, Balachander J, Jayasettiaseelon E, Sreekanth Y, et al. A randomized controlled trial to study the effect of yoga therapy on cardiac function and N terminal pro BNP in heart failure. Integr Med Insights 2014;9:1-6.  Back to cited text no. 4
    
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Telles S, Sharma SK, Yadav A, Singh N, Balkrishna A. A comparative controlled trial comparing the effects of yoga and walking for overweight and obese adults. Med Sci Monit 2014;20:894-904.  Back to cited text no. 5
    
6.
Bhat S, Varambally S, Karmani S, Govindaraj R, Gangadhar BN. Designing and validation of a yoga-based intervention for obsessive compulsive disorder. Int Rev Psychiatry 2016;28:327-33.  Back to cited text no. 6
    
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Pullen PR. The benefits of yoga therapy for heart failure patients. Diss Abstr Int Sect B Sci Eng 2010;71:1-6.  Back to cited text no. 7
    
8.
Ugolini D, Neri M, Cesario A, Marazzi G, Milazzo D, Volterrani M, et al. Bibliometric analysis of literature in cerebrovascular and cardiovascular diseases rehabilitation: Growing numbers, reducing impact factor. Arch Phys Med Rehabil 2013;94:324-31.  Back to cited text no. 8
    
9.
Innes KE, Vincent HK, Taylor AG. Chronic stress and insulin resistance-related indices of cardiovascular disease risk, part 2: A potential role for mind-body therapies. Altern Ther Health Med 2007;13:44-51.  Back to cited text no. 9
    
10.
Khalsa SB. Yoga as a therapeutic intervention: A bibliometric analysis of published research studies. Indian J Physiol Pharmacol 2004;48:269-85.  Back to cited text no. 10
    

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Correspondence Address:
K N Srihari Sharma
#4, 1st Main, 1st D Cross, Manuvana, Vijayanagar, Bengaluru - 560 040, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijoy.IJOY_6_18

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