- This was a meta-analysis of randomized control trials.
- A total of 6 articles involving 182 interventions and 168 controls were included.
- Meta-analysis of BMD at lumbar spine showed no heterogeneity.
- Attrition bias, reporting bias and other bias of the included articles were low.
Objective: This study aimed to evaluate the effects of Tai Chi intervention on bone mineral density (BMD) in postmenopausal women using a meta-analysis of relative randomized control trials (RCTs).
Mehtods: A literature search was conducted though PubMed, Embase, Springer link, The Cochrane library, Wanfang and China National Knowledge Infrastructure (CNKI) until August 11th 2014. The quality of the included articles was assessed using the tool of risk assessment. Heterogeneity across articles was assessed using a Cochran Q test and I2 statistic. The random effects model or fixed effects model was performed based on the heterogeneity results. BMD values were pooled using the weighted mean difference (WMD) method combined with 95% confidence interval (CI). All analysis was conducted using Review Manager Version 5.2.
Results: Six articles involving 182 interventions and 168 controls were eligible for inclusion. Meta-analysis of BMD at lumber spine (Tai Chi vs. control) showed no significant heterogeneity (I2 = 0%, P = 0.89), the fixed effect model was used to pool the data, while, the random effects model to pool BMD at femoral neck because of significant heterogeneity (I2 = 60%, P = 0.12). A meta-analysis of the included RCTs assessing BMD at both lumbar spine (MD = 0.02, 95%CI = -0.00-0.02, P = 0.08) and femoral neck (MD = 0.01, 95%CI = -0.03-0.05, P = 0.51) showed no significant effects.
Conclusions: Tai Chi may have no significant effects on BMD in postmenopausal women.
Key words: bone mineral density; meta-analysis; randomized control trials; Tai Chi
Osteoporosishas been a significant public health problem [1, 2]. It increases the risk of age-related fractures among elderly postmenopausal women . Especially, hip and spine fractures caused by osteoporosis are associated with high morbidity and mortality in these populations [4-6]. Currently, bone mineral density (BMD) has been considered to be the best single predictor of future fracture, and effective drugs aimed at maximizing peak BMD and preventing excessive bone loss was investigated . However, treatment of osteoporotic fractures with medicine required significant long-term and high medical costs and always had side-effects for patients [7, 8]. Nowadays, regular physical activity, having a positive influence on quality of life, is suggested as a possible regimen against involutional bone loss .
Tai Chi, as one of the regular physical activities for health and fitness, has been practiced in China for many centuries and becomes more popular worldwide [10, 11].It is predominantly performed by older individuals . Tai Chi can effectively improve physical flexibility and functional balance by enhancing lower-extremity strength and improving postural stability . It was demonstrated that Tai Chi could reduce blood pressure, be favorable for lipid profile changes, and relieve anxiety status in subjects under well-designed conditions . In addition, Tai Chi plays an important role in decreasing the number of falls, the risk for falling, and the fear of falling in the elder people . Tai Chi can also be beneficial in increasing cardiovascular fitness . However, the effect of Tai Chi on BMD in postmenopausal women is not well understood. Therefore, we felt that there was a necessity to explore the association of Tai Chi and BMD.
In the present study, we aimed to evaluate the effects of Tai Chi interventions on BMD in postmenopausal women by conducting a comprehensive meta-analytic review of the relevant randomized controlled trials (RCT).
Material and methods
Data sources and search strategy
A literature search was conducted using both English databases (PubMed, Embase, Springer link, The Cochrane library) and Chinese databases (Wanfang, China National Knowledge Infrastructure (CNKI)) until August 11th 2014. The searching keywords were as follows: “Tai Ji” or “Tai Chi” or “Tai Ji quan” and “Osteoporosis” or “Bone density” and “Postmenopausal” or “Menopause or elderly”. There is no language restriction. Besides, we manually examined the reference lists of the retrieved papers for additional relevant articles. The electronic databases were retrieved by two investigators independently. Disagreements among them were solved by discussion.
Inclusion and exclusion criteria
Articles were included in this meta-analysis when they met the inclusion criteria as follows: (1) articles with design of RCT; (2) postmenopausal women were involved as the subjects; (3) women in interventions performed Tai Chi or Tai Chi pushing hand (4) women in controls without exercises intervention; (5) BMD were measured at lumbar spine, femoral neck, distal tibia; (6) dual energy x-ray absorptiometry (DEXA) was used to measure BMD; (7) no significant difference at baseline was observed between the interventions and controls.
The exclusion criteria were: (1) articles with non-RCT; (2) articles with incomplete data or the results of BMD measurement were unavailable for statistical analysis; (3) reviews or letters or comments.
Data extraction and quality assessment
After literature selection, the two investigators independently extracted the data independently according to the standard protocol. Data items of included article details, such as the first author’s name, publication year of article, and characteristics of participants, such as age, gender, location, sample size of training group and control group, training frequency and results of each article, were extracted. Disagreements among them were resolved by their discussion.
The quality of the included articles was assessed using the tool of risk assessment according to Cochrane Handbook for systematic reviews of interventions . The Cochrane Collaboration is strongly encouraging the use of a newly developed tool, the Cochrane Collaboration Risk of Bias Tool (CCRBT), for all review groups. There were 7 aspects involved in this risk assessment, including random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting and other bias, through which these biases were evaluated objectively and comprehensively.
The article effect size estimates was pooled using the weighted mean difference (WMD) method combined with 95% confidence interval (CI), as BMD values in interventions and controls after follow-up visit are continuous data. Heterogeneity across trials was tested using a Cochran Q test and I2statistic. If significant heterogeneity was identified (P < 0.05, I2 > 50%), the random effects model was performed to pool the data, otherwise, the fixed effects model was used. All analysis was conducted using Review Manager Version 5.2 (RevMan 5.2; The Cochrane Collaboration, Oxford, UK).
Results of literature selection
The process of search strategy was shown in Figure 1. The original search yielded 291 citations (PubMed: 39, Embase: 47, Springer link: 103, Cochrane library: 8, Wanfang: 55, CNKI: 39). There were 183 articles remained after duplicates removed. Totally, 171 articles were excluded after title and abstract review because of obvious irrelevance. Six among the remained 12 articles were removed for full-text review: 1 for case-control articles; 5 for absent of available data. Manual searching did not contribute additional articles. Finally, 6 articles [18-23] were included for this meta-analysis.
Characteristics of eligible articles
The relevant data from the selected articles were summarized in table 1. The 6 articles were published between 2004 and 2012, and involved 350 objects consisting of 182 intervened with Tai Chi and 168 controls. Populations were Chinese except the objects in Wayne et al. . The time of experimental intervention ranged from 20 weeks to 12 months. In addition, there were two experimental interventions (Tai Chi and Tai Chi pushing hand) in Zhou , thus, there were actually 7 randomized controlled trials. Figure 2 and 3 illustrates the results of quality assessment of the included articles. The selection bias, performance bias and detection bias were high, while the attrition bias, reporting bias and other bias were low, as most of the included articles did not definitely describe the random method or whether used blind method. The overall publication bias was moderate, as well as the quality of the included articles.
Comparison of experimental results
Comparison of BMD at lumbar spine and femoral neck after experimental intervention was performed due to no significant differences exited onBMD at basic line between interventions and controls. Meta-analysis of BMD at lumber spine (Tai Chi vs. control) indicated no significant heterogeneity (I2 = 0%, P = 0.89), the fixed effect model was used to pool the data of BMD. The overall results were also showed in Figure 4 (MD = 0.02, 95%CI = -0.00-0.05, P = 0.08). Significant heterogeneity (I2 = 60%, P = 0.12) was observed in the meta-analysis of BMD at femoral neck (Tai Chi vs. control), thus we chose the random effects model to show the overall results (MD = 0.01, 95%CI = -0.03-0.05, P = 0.51; Figure 5).
Osteoporotic fractures caused by low BMD commonly leads to disability and mortality in postmenopausal women . Exercise plays an important role in reducing the risk of osteoporosis, and Tai Chi has become a popular choice of exercise for elders . In the present meta-analysis, a quantitative analysis of available RCTs was performed to investigate whether Tai Chi has protective effect on BMD in postmenopausal women. A total of 6 articles involving 182 interventions and 168 controls were included in our meta-analysis. The overall results showed that BMD at both lumbar spine and femoral neck intervened by Tai Chi or Tai Chi pushing hand had no remarkable difference compared to controls. These findings suggest that Tai Chi may have no efficacy for preserving BMD in postmenopausal women.
The results were out of our expectation, but Tai Chi was declared to have protective effects on BMD in previous studies. It plays a significant role in retarding age-related deterioration of the musculoskeletal system . Tai Chi can strengthen quadriceps muscle especially for the lower extremities . Evidence demonstrated BMD at the greater trochanter in the participants were higher after Tai Chi intervention . In addition, more than 3 years Tai Chi practice has been reported to increase BMD at spine and hip and improve neuromuscular function in postmenopausal women through retardation of the age-related bone loss . Thus, we felt that Tai Chi may contribute to the regional variations in BMD.
Except the benefits on BMD, Tai Chi, as a form of moderate exercise, can effectively reduce falls [28, 29] and decreasing blood pressure . Cardiorespiratory benefits can be attributable to a sustained effect from the Tai Chi intervention via the increased heart rate, increased noradrenaline exertion, and decreased salivary cortisol concentration, which produces less tension, depression, fatigue, and state-anxiety [31, 32]. Tai Chi is fluidly movement with less strain, and may be beneficial for osteoarthritis or rheumatoid arthritis . Tai Chi may enhance the capacity of the immune system by increasing the level of IgG (human serum immunoglobulin), and significantly decreasing the level of IgM. Then the numbers and activity of natural killer cells in the peripheral blood increased, as well as the level of cortisone. Under this condition, the capacity of the immune system were moderated in elderly people . Long-term practice of Tai Chi can enhance knee extensor strength and quadriceps strengths and lower foot center of pressure displacement, thus to resistance the atrophy of type II muscle fibers . Besides, Tai Chi, as a culturally appropriate mind-body exercise for older adults, is related to improvement in psychosocial well-being, and stress reduction . Tai Chi has a positive effect in reducing depressive symptoms. Moreover, Tai Chi is equally effective in reducing all four categories of depressive symptoms including somatic symptoms, psychological symptoms, symptoms related to interpersonal relation, and symptoms associated with well-being . Comprehensively, Tai Chi is a benefit exercise, having plenty of advantage for human physical well-being.
Previous meta-analysis uncovered that exercise training programs have the capability to prevent or reverse bone loss in the lumbar spine and the femoral neck of postmenopausal women . Another meta-analysis indicated walking has significant, positive effects at femoral neck in postmenopausal women while no significant effect on lumbar spine BMD . This leads us to conjecture that different exercise therapy may affect BMD at different body part. In our meta-analysis, BMD at distal tibia or hip was not considered due to only one included article measured BMD at distal tibia or hip. The benefit effects of Tai Chi on bone mass may be time-dependent, as time is one of the most important factors during the study of physical and psychological interventions . However, the follow-up time was short in these included RCTs. Thus, our results may be suggestive only.
Although the results suggest Tai Chi may have no efficacy for preserving BMD in postmenopausal women, our study still has some advantages. Firstly, the included articles were RCTs with fewer confounding factors, indicating a high reliability. Secondly, heterogeneity across the included articles which described BMD at lumber spine (Tai Chi vs. control) was not obvious. Thirdly, the basic line of age and BMD in subjects had no significant differences.
Of course, there were several limitations in our meta-analysis. Given that the number of the included studies was less, we did not evaluate publication bias. Our results were suggestive only because of the small sample size included in the present study. Therefore, further study is required replicate our preliminary findings with larger sample size in the future. Besides, the follow-up time was short in these included RCTs, as a result, the strengthen effect on BMD might be inconspicuous. Tai Chi originated in China and prevailed for Chinese, thus, participants in the included RCTs were mostly Chinese population.
In conclusion, Tai Chi has no statistically significant effect for protecting BMD in postmenopausal women. Further study regarding Tai Chi for preserving BMD in this population is required for revision involving RCTs with larger sample sizes and higher quality.