Summary of main findings

The results of this systematic review demonstrate that compared to inactive controls, it is possible for older adults to improve many aspects of their physical function and HRQoL through participating in a yoga intervention. Findings suggest that small to moderate sized beneficial effects can be achieved for balance, lower body flexibility, lower limb strength, depression, perceived mental health, perceived physical health, sleep quality, and vitality. When yoga was compared with active controls, statistically significant small to moderate effects favouring yoga were found for lower body strength, lower body flexibility and depression. Yoga was found to be as good as the activity undertaken by active controls in improving outcomes such as mobility, walking speed, balance, anxiety and perceived mental health. The yoga group was never significantly worse than the active or inactive group for any of the outcomes. With high attendance rates for class-based sessions, yoga is a feasible intervention that can be recommended to older adults as an activity that improves physical and mental wellbeing.

Comparison to previous literature

While other systematic reviews have included or focused on studies that recruited older adults with clinical conditions, this review is the first to provide a comprehensive overview of the effects of yoga on physical function and HRQoL in an older adult population not characterised by a specific disease or condition. Outcomes such as depression, perceived mental and physical health, balance and mobility have been evaluated by other meta-analysis of RCTs in an older adult population (5), and are described in the section below.

Physical function

Youkhana et al. [10] conducted a systematic review to assess the effects of yoga on balance and mobility. Since the control groups in the review consisted of no intervention, waitlist control/usual care and provision of an education booklet, the study results can be contrasted with the inactive controls groups of the present study. Although the direction of the effect for balance is similar between the two reviews, the effect size in the inactive control group in this study is much higher than in the Youkhana et al. review (Table 5). The meta-analysis for balance in their review included six studies, with three studies in common with the inactive control group. The difference in effect size could be because of the extremely high effect size in one study included only in the current review, in which participants with poor balance were recruited, and saw great benefits from the yoga intervention [76]. Heterogeneity was lower and non-significant in their review for balance compared to the inactive control group in the current study. This could be attributed to more variation in the yoga types, as well as the inclusion of participants with poor balance at base-line in the current review.

Table 5 Comparison of effect sizes from previous reviews and the current review Full size table

The two reviews used different tests to assess mobility. Hence, a meta-analysis was conducted for mobility in the review by Youkhana et al. [10], but not in the current review while comparing yoga with inactive controls. The current study assessed mobility using the timed-up-and-go test (Additional file 9), which was measured only by two studies, and hence no meta-analysis was conducted. In the meta-analysis by Youkhana et al. [10], mobility was measured in three studies using the timed-eight-foot-walk, sit-to-stand test and the 4-m-walk. Two of the three studies [64, 73] were also included in the current review, with the sit-to-stand test included under strength and the 4-m-walk included under walking speed (Additional file 9).

HRQoL

Two reviews conducted meta-analyses to assess the effects of yoga on perceived mental and physical health in older adults [11, 13], and found a significant positive effect favouring yoga.

A smaller effect size was found for these outcomes in the Tulloch et al. review [13] compared to the current study (Table 5). The effect size in the present study for perceived physical and mental health in the inactive control group can be compared to HRQoL and mental wellbeing in the meta-analysis by Tulloch et al. correspondingly. The smaller effect size may be attributed to differences in inclusion criteria (studies which specifically recruited clinical populations were excluded in the current study), and only four of the 12 studies in the Tulloch et al. meta-analysis overlapped with the inactive control group of the present study. Some studies included in the current review [39, 65] were not captured by the Tulloch review due to differing search strategies, and search dates. The effect sizes for perceived physical and mental health in the meta-analysis by Patel et al. [11] were comparable to that of the inactive control group in the current study. Their review also assessed depression, and although a moderate effect size was found, it was not significant. The current meta-analysis for depression included more studies and may have the power to detect differences between groups. In line with the results of the current review, another systematic review published in Chinese [9] concluded that yoga significantly reduced depressive symptoms and improved quality of sleep in older adults.

Strengths and limitations

This systematic review and meta-analysis offers a comprehensive view of the effectiveness of yoga on both physical and psychological outcomes. The method of segregating controls into active and inactive groups has not been adopted by any other systematic review for this age group, and is a significant strength of this study. The review provides novel and valuable information on the effects of yoga on some salient outcomes like strength, vitality, and social health in an older adult population. No yoga RCT has directly assessed strength in older adults using techniques like isokinetic dynamometry (gold standard) or hand-held dynamometry [79]. To our knowledge this is the first study to conduct a meta-analysis to comment on the effectiveness of yoga in improving strength albeit using a functional fitness measure as a proxy (sit-to-stand test). The sit-to-stand test is a reliable and valid indicator of lower body strength in older adults [80]. Used in conjunction with measures of flexibility, balance, mobility and walking speed, the sit-to-stand test is a fitting indicator of functional fitness and the ability to perform everyday activities in older adults [81].

This study had a broad search strategy, and criteria other than yoga and older adults were applied only at the screening stage, making it less likely to miss out studies. The review also included dissertations, which were not included in some previous reviews [11], leading to more robust results. However, the authors had difficulties in securing quantitative data for non-significant outcomes for some included studies (selective reporting bias) [53, 59], and these could not be incorporated in the meta-analysis. Consideration of this bias is critical since the primary studies test numerous outcomes, increasing the chance of type 2 errors. The inclusion of articles only published in English can be considered a limitation of the review. However, the review has captured studies from across the world including non-English speaking countries such as India, Taiwan, Brazil, and Iran. Only three studies [71, 73, 77] actually included adverse events as an outcome at the onset of the intervention. While eight studies reported on adverse events in the yoga group, it is not evident if there were no adverse events in the other studies, or if they were not reported. In one study [67] it is not clear if the injuries reported can be attributed to the yoga intervention. Ambiguous or no reporting of adverse events is a deficiency in yoga research, which future studies should address. While only a small proportion of included studies have been rated as high risk of bias, several studies have unclear risk of bias for random sequence generation, allocation concealment and blinding of outcome assessment. Future studies should ensure that randomisation and data collection procedures are reported in detail to allow for accurate assessment of bias and reliability of intervention effects.

The classification of test and instruments into broad physical function and HRQoL categories was carried out in a structured manner, referring to literature when available, to support the decisions made. However, this process can be subjective, and could be the root of differences in effect sizes between reviews (for example, sit-to-stand test was classified as assessing mobility in the Youkhana et al. review [10], but was categorised as evaluating lower limb strength in the present review).

Implications for policy and practice

The study offers clear evidence that compared to no activity, yoga improves physical function and psychological wellbeing in older adults. It can be inferred from the meta-analysis results that yoga improves muscle strength and balance. Previous systematic reviews have highlighted the potential of yoga in improving balance in healthy adults [82], and PA policy should continue to promote yoga within muscle strength and balance guidelines to enhance and maintain health. Approximately 15% of older adults are likely to suffer from a mental health disorder [83], with depression affecting 22% of older men and 28% of older women in the UK [84]. Mental wellbeing is critical for an older adult population, and this review highlights the beneficial effects of yoga in improving perceived physical and mental health, vitality, and alleviating depressive symptoms.

The findings from this review could be used to challenge older adults’ perceptions of yoga. Older adults have the impression that yoga only improves flexibility, and the lack of an aerobic component has been cited as a barrier to yoga participation [85]. The older population and yoga teachers need to be educated on the muscle strength and balance guidelines, and also made aware of the physical function and HRQoL benefits of yoga as evidenced by this study. Information from the studies included in this review (e.g. common yoga postures and class structure) should be shared with yoga teachers. Although not directly examined in relation to effectiveness, the cross tabulation of frequency and duration of class-based sessions (Additional file 10) showed that 60 min on two days a week was the most common, which can be easily translated to practice.

Yoga is a recognised and accepted form of activity in India where it originated. In western countries, although an increasing trend in older adult participation in yoga/pilates has been observed [86,87,88], yoga participation rates still remain low [87, 89, 90]. This review adds to the growing evidence on the benefits of yoga, and researchers should work closely with yoga teachers, studios, fitness centres and policy makers to develop and implement strategies to encourage yoga participation among older adults, tying in with the final aim of increasing participation in muscle strength and balance activities.

Future research

Future intervention studies should include an active control arm, so that conclusions can be drawn with respect to the effectiveness of yoga compared to different exercise programmes. Upper limb strength, hand grip strength, fall frequency, balance confidence, stress and self-efficacy are relevant and important outcomes for this population. The effects of yoga on these outcomes could not be computed through a meta-analysis due to lack of studies, and future research with robust experimental designs should focus on these outcomes. Future systematic reviews for the older adult population should aim to comment on dose-response relationships. The current review assessed the effects of yoga immediately after the intervention, and 28-weeks was the longest follow-up period. Future reviews should assess effects over a longer period, taking into account post-intervention follow-up data. Moreover, this review did not include physiological (e.g. cholesterol, indicators of immune function) and cognitive outcomes (e.g. memory and executive functions) and future reviews could aim to assess these outcomes.

There is a need to develop an appropriate framework for assessing physical function in an older adult population. Health Related Physical Fitness is defined in the American College of Sports Medicine manual as consisting of those specific components of physical fitness that have a relationship with good health, and includes cardio-respiratory fitness, body composition, muscular strength and flexibility [16]. However, it does not include mobility, walking speed, balance and frequency of falls which are important parameters of health for this population. Moreover, clear guidance is needed on the tests and instruments that assess these aspects, with details on whether they are a valid measure of the outcomes assessed. A study may have more than one instrument assessing the same outcome, and there is no standard procedure for choosing which one measure to include in the meta-analysis. This is a potential source of bias, and guidance for this process should be developed to reduce subjectivity.