Researchers have pooled the results of previous studies and report finding “promising evidence” of yoga’s health benefits, specifically in reducing the risk of cardiovascular disease (CVD), as well asmetabolic syndrome.
Compared to doing nothing, or interventions that did not include exercise, yoga reduced body weight by 2.32kg, on average, and also improved body mass index (BMI), blood pressure and cholesterol levels, all of which have a protective effect against CVD.
It also found there was no significant difference between yoga and other types of exercise for improving risk factors for heart disease.
What is not clear from this review is which type of yoga could produce these results. Some types of yoga are more focused on physical activity, while others take a more meditative, slow-paced approach.
It should also be noted that there were some limitations to the evidence available. Most of the studies were small and rated as only of moderate quality. The results need confirmation in larger, more robust studies, ideally ones which assess heart disease, as well as its risk factors.
Hopefully, as the researchers suggest, yoga could be an ideal option for people unable to take part in exercises such as cycling or brisk walking because of mobility or other problems.
Where did the story come from?
The study was carried out by researchers from Harvard University and Erasmus MS in the Netherlands. There was no external funding.
The study was published in the peer-reviewed European Journal of Preventive Cardiology.
The UK media reported the results of the study reasonably accurately, but did not explain that they need to be treated with some caution as they are based on small studies. They have also not made it clear that the study does not pinpoint how much and what type of yoga is beneficial.
Only BBC News and the Daily Mail pointed out there are many different forms of yoga, some more strenuous than others.
What kind of research was this?
This was a systematic review and meta-analysis of all relevant randomised controlled trials (RCTs) that looked at the effect of yoga on risk factors for cardiovascular (heart and vascular system) disease. This type of study is the best way of identifying and pooling the results of all of the studies on a particular research question.
The current review only includes studies that have been published, which means that it can be open to finding a greater effect of the intervention than actually exists – this is called “publication bias”. This is because studies which do not show that an intervention is effective are less likely to be submitted to and chosen by journals for publication.
What did the research involve?
Medical databases were searched for all RCTs on the effectiveness of yoga at reducing risk factors for cardiovascular disease. The researchers assessed which of these RCTs met their inclusion criteria, and then pooled their results where possible to give an overall estimate of the effect of yoga.
These databases were MEDLINE, CINAHL, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews, EMBASE, and PsycINFO. They found 37 relevant RCTs published up to December 2013, and they were able to pool the results of 32 of them.
In total, there were 2,768 adults (53% female) in the studies, with an average age of 50 years. A third of the studies were in healthy people, a fifth were specifically in people who already had cardiovascular risk factors, a quarter in people with diabetes or metabolic syndrome (a group of characteristics which increase cardiovascular risk) and just over a tenth in people with a specific type of heart disease (coronary artery disease).
The studies lasted from three to 52 weeks, during which yoga was compared to:
- usual care or conventional medical therapy in 23% of the RCTs
- waiting list or no intervention in 32%
- exercise in 21% (physical training, cycling, running, brisk walking or resistance training)
- education in 11%
- a form of relaxation in 6%
- diet alone in 4%
- cognitive-based therapy in 2%
What were the basic results?
Overall, the individual studies tended to be small and of moderate quality.
There was no significant difference between yoga and other types of exercise for improving cardiovascular risk factors, such as body weight, BMI or cholesterol levels.
Compared to interventions which did not include exercise, yoga improved:
- BMI -0.77kg/m2 (95% confidence interval (CI) -1.09 to -0.44)
- systolic blood pressure (the higher number) by -5.21mmHg (95% CI -8.01 to -2.42)
- low-density lipoprotein cholesterol by -12.14mg/dl (95% CI -21.8 to -2.48)
- high-density lipoprotein cholesterol by 3.20mg/dl (95% CI 1.86 to 4.54)
- body weight by -2.32kg (95% CI -4.33 to -0.37)
How did the researchers interpret the results?
The researchers conclude that this “review finds emerging evidence to support a role for yoga in improving common modifiable risk factors of CVD [cardiovascular disease] and metabolic syndrome”. They also highlight the “need for larger randomised controlled studies that meet explicit, high-quality methodological standards to ascertain the effects of yoga”.
Overall, this review suggests that yoga may be beneficial in reducing risk factors for cardiovascular disease and metabolic syndrome.
While these are encouraging findings, the authors also caution that these are based on trials with some limitations, including:
- There was a wide variation in the type of yoga practised, the frequency and the length of each session across the studies. This means it is difficult to say what the actual effects of each approach are, as the overall effects are just an average across all of these approaches. Some may have more of an effect and some may have less.
- The review does not report the amount of exercise yoga was compared to, and this could also affect their relative benefits.
- The study participants could not be blinded to the fact that they were doing yoga, which could bias the results. However, this tends to be less of an issue when measuring things such as blood cholesterol levels, which participants can’t influence, as long as the people doing the measurements are blinded to whose samples they are testing.
- Most of the studies only had around 20 to 60 participants, with one study having just nine people; the smaller a study, the more likely it is that results are affected by chance.
The government recommends that adults should do at least 150 minutes of moderate-intensity aerobic activity each week and muscle-strengthening activities on two or more days a week. Some forms of yoga could fit the bill for either of these exercise recommendations.
Further, more robust RCTs are required to prove the specific cardiovascular benefits of yoga, and to assess its effects on heart disease events (such as heart attack or stroke), as well as risk factors.