Tai Chi on psychological well-being: systematic review and meta-analysis

Mental illness affects 450 million people worldwide with 25% of the population affected in their lifetimes[1]. It is a leading cause of disability for people aged 15-44[2]. A growing list of psychological states including stress, anxiety, depression and mood disturbance have been linked to many chronic disorders such as coronary heart disease, cancer, diabetes and mental disorders as well as to accidents [3, 4]. Mental illness poses significant economic burdens to those involved, reduces productivity and increases health care costs[5]. Thus, there is an urgent need for inexpensive and effective strategies to promote psychological well-being and improve general heath status, especially for people with chronic conditions.

Over the past decade, evidence from epidemiological studies and clinical trials has demonstrated a positive association between physical fitness and psychological health. Numerous studies have shown that physical activity and exercise as well as mind-body practice reduce morbidity and mortality for coronary heart disease, hypertension, obesity, diabetes and osteoporosis, and improve the psychological status of the general population [6‐10].

Tai Chi, a form of Chinese low impact mind-body exercise, has been practiced for centuries for health and fitness in the East and is currently gaining popularity in the West. Our previous investigations have shown that Tai Chi has potential benefits in treating a variety of chronic conditions [11‐13]. Significant improvement has been reported in balance, strength, flexibility, cardiovascular and respiratory function, as well as pain reduction and improved quality of life [11]. Several recent reviews have suggested that Tai Chi appears to improve mood and enhance overall psychological well-being [11, 14, 15]. However, convincing quantitative evidence to estimate treatment effects has been lacking. No meta-analysis addressing any psychological outcomes with Tai Chi has ever been published. To better inform patients and physicians, we systematically reviewed the quantitative and qualitative relationship between Tai Chi and psychological health outcomes (stress, anxiety, depression, mood and self-esteem) by critically appraising and synthesizing the evidence from all published studies of healthy and chronically ill populations in the East and West.

We reviewed 2579 English and Chinese articles and retrieved 61 full-text articles for detailed evaluation (Figure 1). Twenty-one studies were eliminated for not reporting original or relevant psychological outcome data. Ultimately, forty studies were identified for data abstraction and critical appraisal. Our search did not identify any unpublished literature.

Table 1 lists the study design and number of studies and participants for each psychological domain. Table 2 describes the 40 studies including 17 RCTs, sixteen NRS and 7 OBS published between 1980 and 2009. They were conducted in 6 countries (USA, China, France, Germany, UK and Australia). There were 3072 healthy individuals (25 studies) and 745 patients with chronic conditions (14 studies); no data were available in 1 study [22]. Mean age ranged from 11 to 92 years, and 62% of participants were female. Various controls were compared among the 17 RCTs, with 6 studies having multiple types of controls. Fourteen of the 16 NRS were self-comparisons while 2 used routine activity as controls. Three of the 7 OBS used routine activity, two used aerobic activity, one was a self-comparison and 1 used the general population as comparisons.

Nine RCTs reported on randomization; eight of these described an appropriate method, one an inappropriate one. Ten RCTs reported on blinding; in all 10, outcome assessors were blinded. Twelve studies described withdrawals and dropouts. Dropout rates were high with 4 studies reporting dropouts ≥ 25%, and 3 others that reported attrition of 32%, 35%, and 47%. Eleven NRS and 6 OBS reported dropouts, with high rates listed for 3 NRS, reporting 57%, 43% and 33% (Table 2).

In all, we included 21 trials (12 RCTs and 9 NRS) of 33 that provided data on psychological quantitative measures in the meta-analysis. The 7 OBS were not included in the meta-analysis. Figure 2 displays the overall effects of Tai Chi on stress, anxiety, depression and mood. Table 3 qualitatively assesses the 19 studies that were excluded from the meta-analysis, showing study characteristics, methodology quality, and psychological outcomes. We describe below results for each outcome separately for studies that provided data for meta-analysis and those excluded from meta-analysis.

Five RCTs, five NRS and 1 OBS, conducted in 4 countries (USA, Australia, Germany and China) reported the effects of Tai Chi on stress in 870 participants with ages ranging from 16 to 85 years (Table 2). Most studies employed subjective stress measures, including the Depression, Anxiety, Stress Scale [23], Exercise Experiences Scale [24], Self-Perceived Stress score [25], Perceived Mental Stress score, Functional Assessment of HIV Infection [26], Impact of Event Scale [27], Perceived Stress Scale [28], and the Chinese Psychological Stress Scores. Two objective measures collected were body temperature[29] and salivary cortisol levels [30, 31].

Five RCTs, 9 NRS and 5 OBS investigated the anxiety-reducing effect of Tai Chi in 1869 people from 4 countries (USA, UK, Australia and China) (Table 2). Seven studies used the Profile of Mood States Anxiety subscale[42] and 6 employed the State-Trait Anxiety Inventory [43]. The remainder used: the Depression, Anxiety, Stress Scale [23], Connors' Teacher Rating Scale-Revised [44], Taylor Manifest Anxiety Scale [45], State Anxiety Inventory[46] and Zung Self-Rating Anxiety Scale [47]. Two disease-specific anxiety measures were used: the Symptom Checklist-90[48] and the Fibromyalgia Impact Questionnaire [49].

Ten RCTs, 6 NRS and 4 OBS examined the effects of Tai Chi on depression in 2008 subjects. Tai Chi intervention ranged from a single 1-hour session to 14 years. Six studies used the Center for Epidemiology Studies Depression Scale [64]. Seven used the Profile of Mood States Depression subscale [42], and the rest tests were the Beck Depression Inventory [65], Fibromyalgia Impact Questionnaire [49], Zung Self-Rating Depression Scale[66] and Self-Rating Scale-90.

Evidence on the effects of Tai Chi on mood was examined from 4 RCTs, eight NRS and 3 OBS in 1613 subjects. Duration of Tai Chi practice ranged from 1 hour to 14 years (1 to 7 times a week). The majority of studies reported the total score of the Profile of Mood States scale [42]; other measures were the Functional Assessment of HIV Infection [26], Positive and Negative Affect Schedule [73], Life Satisfaction in the Elderly Scale [74], Symptom Checklist-90 [48], Conners' Teacher Rating Scale-Revised [44], and Multiple Affect Adjective Checklist-Revised [75].

Tai Chi, a form of low impact mind-body exercise, has spread worldwide over the past two decades. This systematic review and meta-analysis summarizes and updates results of the effects of Tai Chi exercise on health outcomes[11] in terms of psychological effects in various populations.

Evidence accrued from clinical trials and observational studies indicates that Tai Chi-- both short and long-term--appears to have mental health benefits in promoting psychological well-being, self-esteem and life satisfaction among healthy subjects and patients with chronic conditions. Specifically, twenty-three of the 33 RCTs and NRS from our quantitative meta-analysis and qualitative evidence synthesis reported that 1 hour to 1 year of regular Tai Chi activity significantly reduced stress, anxiety and depression, and enhanced mood in healthy adults and patients with chronic conditions. The 7 OBS with relatively large sample sizes reinforce the beneficial effects of Tai Chi on psychological health, although bias may be inherent in these observational data.

Our review is congruent with other recent epidemiological reports, experimental trials and literature reviews supporting the fact that physical activity and exercise are associated with better psychological health [8, 14, 15, 86]. Biddle et al recently reviewed evidence on physical activity and exercise in relation to different aspects of mental health. They found that exercise is associated with the strongest anxiety-reduction effects and emphasized the causal link between physical activities and reduction in clinically-defined depression [18]. In particular, evidence from meta-analyses and narrative reviews demonstrates that physical activity and exercise as well as mind-body practice have consistently been associated with positive mood and affect [10, 14, 15, 87‐89].

There is insufficient evidence to find any dose-response effect of Tai Chi for psychological outcomes. The studies included in this review exhibit a wide variety of Tai Chi styles, frequency, duration and follow up. The Yang style was used in 17 studies. The majority of studies featured Tai Chi 2 to 3 times per week (frequency), for at least 20 minutes and for an average of 40 to 60 minutes per session (duration). The length of exercise programs ranged from 5 weeks to 1 year, or a single hour for two studies. In the OBS, Tai Chi duration ranged from 6 months to 14 years, and all studies found positive psychological benefits. Few studies reported the intensity and relationship between adherence to Tai Chi and positive psychological effects. Further studies are needed to optimize effective evidence-based dose-response effects and should strictly demand descriptions of intensity, frequency, duration and adherence of the Tai Chi exercise.

Tai Chi appears to be an effective therapeutic modality to improve psychological well-being among various populations. However, it is still difficult to draw firm conclusions. First, we did not include any unpublished studies. The overall methodological quality of previous studies is unsatisfactory, consisting mostly of small sized or nonrandomized comparisons. Given the few high quality RCTs available for investigation, our review is limited by wide variations in methodological rigor of clinical trials and observational studies. Second, the heterogeneous amalgamation of instruments used to collect clinical psychological health data restricts our ability to evaluate differences in these outcomes. Third, it remains unclear whether Tai Chi mind-body exercise provides equal or superior psychological benefits compared to moderate-intensity aerobic exercises. Fourth, most studies failed to provide objective measures of stress and anxiety such as salivary cortisol level, blood pressure or heart rate, and some studies only reported a subset of psychological outcomes. Due to the limited physiological variables in our analyses, we were unable to analyze the effect of Tai Chi on physiological effects. Fifth, the studies included in the meta-analyses demonstrated a relatively high degree of heterogeneity. Various patient populations were used, and most studies involved healthy people. There were also many variations between the included studies with regard to methodological quality (eg, problems of randomization, allocation concealment, or reporting results), which prohibited us from analyzing the quantitative evidence. However, it is difficult to compare results across studies because they were assessed at different time points. Additionally, all the studies published in mainland China, Hong Kong and Taiwan reported unanimously positive results. Differences in methodological rigor between eastern and western studies may be potential sources of heterogeneity, and publication bias may vary across countries and cultures.

Few published studies have specifically investigated the underlying mechanism of action of Tai Chi's effects on psychological health. Many intermediate, but unidentified, variables may lie along the pathway from Tai Chi to improved psychological well-being. Measures of psychological variables and a multitude of other outcome measures are empirically inter-related, and treatment of each outcome can reciprocally and exponentially improve the other. Improvement of psychological status is also associated with improvement in other clinical outcomes such as arthritic pain as well as health status [90]. The possible mechanisms for enhanced psychological health resulting from Tai Chi mind-body exercise may therefore act through its beneficial influence on biological, physiological, cardiovascular, neurological, and immunological effects as well as overall well-being [11, 67, 89, 91].

In conclusion, the results of these studies suggest that Tai Chi may be associated with improvements in psychological well-being including reduced stress, anxiety, depression and mood disturbance, and increased self-esteem. High-quality, rigorous, prospective, well-controlled randomized trials with appropriate comparison groups and validated outcome measures are needed to further understand the effects of Tai Chi as an intervention for specific psychological conditions in different populations. Knowledge about the physiological and psychological effects of Tai Chi exercise may lead to new complementary and alternative medical approaches to promote health, treat chronic medical conditions, better inform clinical decisions and further explicate the mechanisms of successful mind-body medicine.