Commentary on “Yoga in Coronary Artery Disease”

OVERVIEW OF THE STUDY The systematic review and meta-analysis by Neto et al.[1] from Brazil examines the intersection of mindful practices such as yoga, coronary artery disease (CAD), psychological stress, depression, peak oxygen consumption, and blood pressure. Peak oxygen consumption is frequently used as a measure of cardiorespiratory and general health and overall aerobic capacity, and measures maximal oxygen consumption (VO2 max) during physical exertion. Thus, higher VO2 max values correlate with better cardiovascular health, while reductions in VO2 max values occurs with age, obesity, sedentary lifestyles, etc. The study by Neto et al.[1] compared an intervention group (yoga) with a control group (no exercise or usual care) based on reports from 17 studies with sample sizes ranging from 42 to 3,921 patients with CAD, where the percentage of male participants ranged from 68 to 100. Notably, all data were collected in India, with the exception of one study by Tillin et al.[2] that was performed in the UK but using mainly male participants (78%) largely of South Asian (60%) ancestry, and another from Poland by Grabara et al.[3] with only male participants. Of importance is that all the participants included in the studies by Neto et al.[1] were aged 50 years or more, with the mean age range of the participants in these studies being 50–72 years old. Importantly, the reporting of some studies lacked details of patient demographics. The effects of yoga on some outcomes are summarized below: Anxiety: No clear effects of yoga on scores of anxiety. Depression: Moderate benefits of yoga. Stress: Moderate benefits of yoga. Quality of life: Low quality of evidence supporting benefits of yoga. Peak oxygen consumption: Modest increases in peak VO2. Blood pressure: Reduction (systolic: −3.2 mmHg; diastolic: −2.42 mmHg) in yoga intervention group. The studies included in the meta-analysis were mostly from India and largely of poor methodological quality. Although there was low-quality evidence that yoga improved psychological symptoms, the data are self-reported perceptions and subjective in nature as many trials lacked clarity on design principles (e.g., no data on blinding, sample size calculation, and intension to treat analysis). The reductions in systolic, diastolic, mean blood pressures, and perceived stress were not accompanied by plasma markers of cortisol, angiotensin, catecholamines, and endothelial factors. Previous reports indicated that yoga had negligible effects on mortality, frequency of angina, or modifiable cardiovascular risk factors, possibly indicating an important role for other lifestyle factors.[4] Twelve-week yoga produced only modest, but nonsignificant, increases in alter markers of cellular aging (telomere lengths) that were accompanied by reductions in markers of oxidative stress and inflammation.[5] LIMITATIONS OF CURRENT RESEARCH IN BENEFITS OF YOGA There are numerous limitations in many of the studies on the benefits of yoga, and this is a generalization that should be acknowledged. Heterogeneity of study designs An important limitation is the large variations in study design in terms of duration, frequency and type of yoga practices. Additional limitations include the diverse outcome measures reported, which often tend to be subjective assessments based on self-reported data. Absence of standardization Studies on the benefits of yoga rarely have standardized protocols, where intervention protocols vary with the expertise of the instructors, which can bias outcomes. Sample selection Most studies on yoga have small sample sizes that often includes elderly subjects with comorbidities, and young subjects from diverse cultural/ethnic backgrounds are poorly represented in most studies. Thus, participants rarely represent the general population, and can lead to cultural biases. Difficulty in blinding The nature of yoga does not lend itself well to blind participants and study organizers to be blind to the interventions, likely creating a bias in the outcomes reported. An additional concern is that the absence of appropriate controls as a placebo effect is difficult to implement in these studies. An approach taken by some is to compare yoga with standardized treatments, but this has its own methodological challenges. OVERVIEW OF HEALTH BENEFITS OF YOGA Yoga is a practice that has evolved over many centuries and that focusses on improving the mind–body connection. It has at least three components: (1) Breathing: Yoga strengthens the interaction between breathing and movement based on the premise that breathing calms the mind and strengthens the mind–body connection. Yoga encompasses several breathing practices; (2) Physical: Several postures that focus on body alignment, sensation and breathing, are practiced in yoga; these can all promote body awareness and flexibility; (3) Meditation and Relaxation: Yoga often involves practices of meditation, relaxation, and mindfulness; these practices create a health self-awareness and promotes mental clarity. Physiological mechanisms The practice of yoga has roots in India and is now popular on a global scale; however, despite its worldwide popularity, little is known about the mechanisms of its therapeutic benefits. The mechanisms can broadly be classified into three categories. Stress Yoga activates the parasympathetic nervous system to lower the stress response by reducing the levels of cortisol (a stress hormone).[6] Yoga also lowers adrenaline levels, so leading to calmness.[7] Inflammation Yoga can inhibit pro-inflammatory signaling and stimulate immune function.[8] Yoga reduces plasma markers of inflammation, such as C-reactive protein and pro-inflammatory cytokines.[9] Cardiovascular Techniques of yoga lowers heart rate, blood pressure, and vascular endothelial function.[10] There is increased interest in measures of heart rate variability (HRV), a measure of the regulation of heart rate by the autonomic nervous system and cardiovascular health. Higher HRV correlates with healthier cardiovascular health – some studies report that yoga increases HRV, likely by promoting parasympathetic regulation of cardiac function. Importantly, stress, inflammation, and cardiovascular dysfunction are all associated with oxidative stress. Yoga lowers oxidative stress, presumably by increasing the metabolism of free radicals (by upregulation endogenous anti-oxidant enzymes) while at the same time also reducing the generation of free radicals – although direct molecular studies are lacking. Psychological mechanisms Mindfulness Yoga improves present-moment awareness (mindfulness) and strengthens emotional regulation to lower states of anxiety, depression, and psychological distress.[11] Cognitive function Regular yoga practice promotes beneficial structural and functional changes in the brain (neuroplasticity) that can lead to improved memory, attention and emotional regulation.[12] Regular yoga increases levels of brain-derived neurotrophic factor (BDNF) – low levels of BDNF are measured in depression, anxiety, and loss of cognitive function. RECENT DEVELOPMENTS The general conclusions of the meta-analysis by Neto et al.[1] find support in the recent findings by Takemura et al.[13] on the many benefits of Tai Chi in 226 patients with lung cancer, where 16-week Tai Chi had the following effects: improving coping mechanisms for psychological distress, reducing anxiety, enhancing sleep quality, and reducing mortality rates. A recent study by Li et al.[14] demonstrated that Tai Chi caused greater reductions in prehypertensive patients compared to the effects of aerobic exercise (−7.0 mmHg vs. −4.6 mmHg) in 342 patients after 12 months. Another study by Chen et al.[15] from China reported that Tai Chi was more effective than walking exercises for improving global markers of cognitive function and for reducing mild cognitive decline in patients (328 patients, 60 years or older) with type 2 diabetes. CONCLUSIONS There are a limited number of high-quality studies on the mind–body connections as a holistic approach to improve the quality of life in healthy people and those with underlying pathologies. While the study by Neto et al.[1] focused on cardiovascular health, it is important to note that yoga also has benefits other health concerns such as depression,[16] addiction,[17] diabetes,[18] flexibility, balance and strength,[19] stroke rehabilitation,[20] and various aspects of mental wellbeing.[21] More studies are needed to better understand the long-term benefits of yoga in healthy and unhealthy subjects, and would benefit by using molecular approaches (including metabolomics, proteomics, etc.) to understand changes at body systems levels. Future studies should address some methodological challenges (e.g., placebo effects, improved study designs, and improved analytical analysis). Conflicts of interest Dr. Ismail Laher is Associate Editor-in-Chief of Heart and Mind. The article was subject to the journal’s standard procedures, with peer review handled independently of Dr. Ismail Laher and the research groups. There are no conflicts of interest.

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