We identified 321 citations of which 107 unique systematic reviews met the criteria
for inclusion in the review 5], 7], 9]–113]. Figure 2 provides a graphic representation of the evidence base. Two thirds (66 %) of the
reviews were published in the last five years and spanned a wide diversity of clinical
indications, study populations, and outcomes.

Fig. 2. Evidence map of Tai Chi. The bubble plot displays Tai Chi research based on systematic
reviews published to February 2014. y-axis: literature size estimate (number of RCTs included in the largest systematic
review). x-axis: effect estimate (three partitions: evidence of potentially no effect, unclear evidence base, evidence of a potential
positive effect). Bubbles: clinical indication. Color: green bubbles indicate that the identified systematic reviews on the topic include a Cochrane review
or an AHRQ evidence report. Bubble size: number of systematic reviews on the topic

Size of research base

Topics with the largest research base included research on general health effects,
psychological well-being, interventions in older adults, and effects on the outcome
balance, hypertension, falls prevention, and cognitive performance.

The evidence base for the effectiveness of Tai Chi was unclear for the five of the
largest areas of research. Six systematic reviews addressed positive effects of Tai
Chi on health outcomes (Health) 7], 16], 36], 55], 59], 78]. The largest review, a comprehensive review of health benefits of qigong and Tai
Chi, included 51 RCTs but did not provide treatment effect estimates across individual
studies 55] and the other reviews primarily highlighted the need for more research. The reviews
included studies that addressed a large range of outcomes. The largest review included
studies that reported on 163 physiological and psychological health outcomes 55]. An AHRQ evidence report on meditation practices required studies to report measurable
data for health-related outcomes and differentiated physiological (e.g., sensory outcomes),
psychosocial (e.g., social and interpersonal relationships), and clinical outcomes
(e.g., longevity) 7]. The other reviews differentiated the outcome categories balance improvement/postural
stability/fall prevention, cardiovascular and ventilator enhancement, and other outcomes
(rheumatoid arthritis, pain reduction, stress reduction, nightmare reduction); 16] included studies reporting on health outcomes such as cardio respiratory function,
falls, balance, strength, or quality of life; 36] reported more than 22 different outcomes addressed in included studies and highlighted
effects on quality of life, physical functioning, pain management, balance and risk
of falls reduction, enhancing immune response, and improving flexibility/strength/kinesthetic
sense; 59] or differentiated effects on cardiovascular disease, chronic disease and immunity,
and psychological benefits 78].

Five systematic reviews concentrated on psychological well-being 24], 32], 56], 95], 111]. The largest review included 37 RCTs, but treatment estimates were only presented
for three of the included RCTs 24]. A meta-analysis reported positive pooled results for a few selected outcomes, 95] two reviews did not provide specific treatment estimates, 56], 111] and one concluded that it is premature to form conclusions on the effect of Tai Chi
on psychological well-being 32]. Four published systematic reviews have examined Tai Chi and qigong for older adults
84], 85], 94], 113]. The review authors focused specifically on this population and did not restrict
the reviews to a particular clinical outcome. The reviews addressed a range of outcomes
and analyses, including perceived benefits to health, perceived improved mediators
such as social support, and perceived factors for initiating Tai Chi; 84] the efficacy of Tai Chi Chuan based on outcomes reported in included studies such
as falls, balance, or cardiorespiratory functions; 94] physical and psychological health outcomes differentiating identified outcomes into
the categories falls and balance, physical function, cardiovascular disease, and psychological
and additional disease-specific responses; 85] and validated measures and self-reported indicators of mental well-being such as
life satisfaction, mental health-related quality of life, self-esteem, or happiness
and mastery 113]. The largest review included 31 RCTs; 85] none of the reviews reported specific treatment estimates for Tai Chi across studies.

The outcome balance has been addressed in nine systematic reviews by independent author
groups 10], 37], 39], 53], 57], 61], 72], 77], 109] and the largest review included 27 RCTs. The largest review did not report treatment
effect estimates 57] and an existing Cochrane review on exercise interventions included 12 Tai Chi RCTs
but reported effects only for a combination of Tai Chi, gi gong, dance, and yoga interventions
53]. Another review pooled three RCTs and found no effect of Tai Chi on the single leg
stance test compared to different control groups 10] while results of studies included in the remaining reviews varied and none of the
reviews provided a treatment effect estimate across identified studies. A systematic
review addressing health-related quality of life included 15 Tai Chi RCTs 28] but did not provide a summary estimate for Tai Chi effects and individual study results
varied within and across studies.

Potentially promising effects

Promising effects of Tai Chi, indicated by statistically significant pooled treatment
effects in systematic reviews, and based on a substantial number of research studies
included findings for hypertension, falls prevention outside of institutions, and
cognitive performance. Hypertension has been addressed in three systematic reviews
68], 97], 106]. The pooled results of the largest review (18 RCTs) showed a larger number of participants
with reduced blood pressure (relative risk [RR] 3.39; 95 % confidence interval [CI]
1.81, 6.34; 4 RCTs); reduced mean systolic blood pressure (mmHg WMD 12.43; 95 % CI
12.24, 12.62; 10 RCTs); and reduced mean diastolic blood pressure (mmHg WMD 6.03;
95 % CI 5.90, 6.16; 10 RCTs) compared to usual care 97]. However, the authors cautioned that the evidence remains weak and stated reservations
due to the poor quality of the included studies, lack of longer follow-up, or conflicting
results across outcomes, comparators, and settings. An earlier review that included
only four RCTs in elderly participants concluded that the evidence for Tai Chi in
reducing blood pressure in the elderly is limited, 68] and the third review did not provide a pooled treatment estimates across studies
106]. Tai Chi for fall prevention in unselected populations or participants living in
the community (Falls-general) has been addressed in ten independent reviews 17], 20], 43], 47], 48], 51], 73], 75], 87], 101]. The largest review (15 RCTs) reported no benefit compared to non-exercise controls
across five studies but found a significant pooled estimate for Tai Chi versus exercise
controls (incidence rate ratio [IRR] 0.51; 95 % CI 0.38, 0.68; 2 RCTs); the review
discussed a number of explanations for this finding, including a dose-response effect
73]. A Cochrane review on interventions for preventing falls in older people living in
the community found no reduction in the rate of falls but reported a significantly
reduced risk of falling (RR 0.71; 95 % CI 0.57, 0.87; 6 RCTs) associated with Tai
Chi compared to diverse, predominantly passive comparators (e.g., wellness education)
47]. An AHRQ report on interventions to prevent falls in older adults included three
Tai Chi RCTs, but no summary treatment effect was reported 20]. A further review reported a statistically significant pooled estimate for Tai Chi
in community-dwelling participants (RR 0.66; 95 % CI 0.52, 0.78; comparators not specified)
17]. One review found no Tai Chi fall RCTs in older persons with cognitive impairment,
and the remaining reviews did not provide a summary effect estimate. Of note, reviews
in hospitals and nursing home settings (Falls-institutions) did not report positive
findings 9], 17].

One systematic review on the effects of Tai Chi on cognitive performance in older
adults identified 11 relevant RCTs 100]. This review found positive effects of Tai Chi on executive function in cognitively
healthy adults compared to no intervention (SMD 0.90; p?=?0.04; 4 RCTs) and exercise (SMD 0.51; p?=?0.003; 2 RCTs), on global cognitive function in cognitively impaired adults compared
with no intervention (SMD 0.35; p?=?0.004; 4 RCTs) or other active interventions (SMD 0.30; p?=?0.002; 4 RCTs). However, it cautioned that larger and methodologically sound trials
with longer follow-up periods are needed before definitive conclusions can be drawn.

There are also a number of areas suggesting promising results but for which the volume
of research is smaller and fewer than ten relevant RCTs were available to inform the
reviews. Eight systematic reviews have addressed osteoarthritis 5], 12], 21], 30], 44], 63], 88], 90], 103], and the two largest reviews included nine RCTs each. One of them reported pooled
results and showed positive effects of Tai Chi compared to different control groups
on pain (SMD ?0.79; 95 % CI ?1.19, ?0.39; 6 RCTs), physical function (SMD ?0.86; 95 %
CI ?1.20, ?0.52; 6 RCTs), and joint stiffness (SMD ?0.53; 95 % CI ?0.99, ?0.08; 6
RCTs) but cautioned that due to the small number of RCTs with a low risk of bias,
the evidence that Tai Chi is effective in patients with osteoarthritis is limited
5]. An independent review reported significant positive short-term effects for pain
intensity (SMD ?0.72; 95 % CI ?1.00, ?0.44; 5 RCTs), function (SMD ?0.72; 95 % CI
?1.01, ?0.44; 5 RCTs), stiffness (SMD ?0.59; 95 % CI ?0.99, ?0.19; 5 RCTs), and physical
quality of life (SMD 0.88; 95 % CI 0.42, 1.34; 2 RCTs) but not for mental quality
of life, or long-term effects for pain, physical function, and stiffness, compared
to waitlist or attention control. The authors highlighted that all positive results
represent short-term effects and high-quality RCTs are needed to confirm the results
63]. A 2013 meta-analysis reported statistically significant and clinically important
effects for pain (SMD ?0.45; 95 % CI ?0.70, ?0.20; 7 RCTs) across studies comparing
Tai Chi to waiting list, Bingo, attention control programs, routine treatment, self-help
programs, or wellness education and stretching, and concluded that 12-week Tai Chi
programs should be included in rehabilitation programs but highlighted that the pain
– relieving effect is not sustained and that additional studies are needed to investigate
the long-term effects of Tai Chi in patients with knee osteoarthritis 103]. The remaining reviews did not identify eligible Tai Chi RCTs for their particular
review question or did not report treatment effects across studies.

Positive outcomes were also reported in two reviews on chronic obstructive pulmonary
disease (COPD) 42], 104] and the largest included eight RCTs. The largest review reported statistically significant
pooled effects of Tai Chi for the 6-min walk test (WMD 34.22 m; 95 % CI 21.25, 47.20;
3 RCTs), dyspnea (WMD –0.86; 95 % CI –1.44, –0.28, 3 RCTs), forced expiratory volume
in 1 s (WMD 0.07; 95 % CI 0.02, 0.13, 4 RCTs), forced vital capacity (WMD 0.12; 95 %
CI 0.00, 0.23, 3 RCTs), and two quality of life measures (WMD 0.95; 95 % CI 0.22,
1.67; 2 RCTs; WMD ?4.08; 95 % CI ?7.52, ?0.64; 3 RCTs), comparator not specified 104]. The second review combined Tai Chi and qigong interventions and did not provide
treatment estimates across Tai Chi studies. Four systematic reviews have focused on
the outcome pain 49], 81], 107], 112] and the largest review included seven RCTs (including six arthritis RCTs). The largest
review found a positive effect of Tai Chi on self-reported pain (WMD 10.1 points on
a 0–100 scale; 95 % CI 6.3, 13.9; 6 RCTs; comparators not specified) and self-reported
disability (WMD ?9.6; 95 % CI ?14, ?5.2; 4 RCTs) but not for physical performance,
and data for quality of life were not pooled across studies 49]. Pooled treatment estimates of Tai Chi across studies were not reported in two other
reviews, and one review found no eligible Tai Chi RCT. Five systematic reviews focused
on balance confidence/fear of falling 15], 18], 33], 83], 91] and the largest included six RCTs. One reported a positive effect for Tai Chi compared
to usual care, exercise, or education (SMD 0.47; 95 % CI 0.30, 0.63; 4 RCTs) 83]. The other reviews did not report a treatment effect estimate across studies. Five
systematic reviews have specifically addressed the effects of Tai Chi on depression;
26], 34], 38], 93], 102] the largest review included four RCTs. It reported statistically significantly reduced
depression symptoms (SMD ?0.27; 95 % CI ?0.52; ?0.02; 4 RCTs) compared to waitlist
in older adults but highlighted that further research is recommended with larger samples
sizes, more clarity on trial design and the intervention, longer-term follow-up, and
concomitant economic evaluations 38]. The other depression-specific reviews included only one or two Tai Chi studies or
did not distinguish effects attributable to Tai Chi. However, the review of psychological
well-being included nine RCTs reporting on depression, and it also reported a positive
effect (Hedges’ g 0.48; 95 % CI 0.17, 0.78) 95]. A review on lower limb muscle strength in the elderly included two RCTs; both reported
positive effects but did not report on the same outcome 11], 114].

Evidence of no effect and unclear or conflicting evidence

The map includes a small number of systematic reviews that provide evidence of the
potential lack of effectiveness of Tai Chi for clinical indications across more than
one included study, e.g., fall prevention in hospitals and nursing homes (see the
left hand side of the map). For these topics, systematic review authors concluded
across identified studies that Tai Chi did not improve outcomes of interest; however,
the number of existing studies in the identified topic areas was small in all of the
identified topic areas.

In addition, unclear or conflicting evidence was found for a large number of topical
areas as shown in the large middle section of the evidence map; in some cases, despite
a number of existing systematic reviews that have attempted to synthesize the evidence
in the research area.

Lack of research

The evidence map also shows clinical topics that have been reviewed, but for which
no Tai Chi studies could be found (y-axis?=?0). Systematic reviews on menopause, dementia, metabolic syndrome, post-traumatic
stress disorder (PTSD), urinary incontinence, multiple sclerosis, and anxiety during
pregnancy systematically searched for Tai Chi studies. However, no RCTs, i.e., research
studies supporting a high level of evidence, were identified in these systematic reviews.

Other evidence base variables

Of the 107 included reviews, 42 % reported on the presence or absence of adverse events
(not shown in Fig. 2). The large majority of these reviews noted that Tai Chi had little or no adverse
effects on study participants. However, doing any exercise may put participants at
greater risk and one review concluded that Tai Chi practiced by older adults may only
be effective in a more robust older population and may not benefit frail participants
48]. None of the included reviews was exclusively based on Tai Chi interventions that
deviated from traditional formats.