Seventy studies were included in the review; one cross-sectional study (n=105), 32 uncontrolled studies (n=930), 15 non-randomised controlled trials (n=692) and 22 RCTs (n=1,214).
Most of the identified studies were small in size, with over 40% containing study populations of under 25 participants. Over 70% of the studies were conducted India. Overall, the studies were of poor quality and had a number of methodological problems, which limited all of the findings below.
Markers of insulin resistance.
Thirteen studies examined the influence of yoga-based interventions on markers of insulin-resistance. Most studies, including 2 RCTs, documented an improvement in one or more indices, following yoga either alone or in combination with other therapies. Improvement varied by study population and study design.
Lipid profiles.
Eleven of the 14 studies that examined the effects of yoga-based interventions on lipid profiles demonstrated an improvement in one or more indices following yoga. Of the 5 RCTs identified (all of adults with hypertension, CVD or risk factors for CVD), three reported an improvement in all of the indices of dyslipidaemia examined, one reported significantly greater reductions in triglycerides but not cholesterol or low-density lipoprotein, and one reported no difference between the intervention and control groups.
Body weight or composition.
Eighteen studies examined the influence of yoga-based interventions on body weight or composition; most studies documented an improvement in one or more indices following yoga, either alone or in combination with other therapies. Four of the 5 RCTs were reported to show a significant improvement with yoga, relative to usual care.
Blood-pressure.
Thirty-seven studies examined the influence of yoga-based interventions on blood-pressure. Twenty-seven studies, including 11 RCTs, were reported to demonstrate a beneficial effect of yoga-based programmes on one or more indices.
Coagulopathy and oxidative stress.
Both studies evaluating coagulation (one uncontrolled study and one non-randomised controlled trial) documented a beneficial effect of yoga-based interventions. Of the 5 studies that assessed the influence of yoga on oxidative stress, all (including 1 RCT) were reported to show a beneficial effect of yoga-based programmes in healthy populations and those with chronic IRS-related disorders.
Sympathetic/parasympathetic activation and cardiovagal function.
Of the 27 studies examining the influence of yoga on heart and/or respiratory rate, 25 demonstrated a positive effect of yoga-based programmes. Of the 7 RCTs, one did not demonstrate a beneficial effect of yoga.
Clinical end points.
Fourteen studies (including 6 RCTs) examined the effect of yoga-based programmes on clinical end points. All of the included studies were reported to have a beneficial effect on clinical end points.