Distress is an increasing public health problem. We aimed to investigate the effects of an Iyengar yoga program on perceived stress and psychological outcomes in distressed women and evaluated a potential dose-effect relationship. Seventy-two female distressed subjects were included into a 3-armed randomized controlled trial and allocated to yoga group 1 (
Several recent studies indicate there is an increasing number of people of Western societies that suffer from distress and stress-related disease. For example, a recent survey of a large German health insurance company found that up to 80% of the general population feel distressed frequently, and 30% feel distressed most of the time [
Yoga is an increasingly used self-care and health-promoting technique in the US and Europe. An estimated 30 million persons, mostly women (72%), had practiced yoga in the US according to a recent survey [
Despite its potential benefits and popularity among distressed people, the effectiveness of yoga in relieving perceived stress has been addressed only in a few randomized controlled trials. One systematic review describes the effects of yoga on stress-associated symptoms; here Chong et al. [
A 3-armed randomized controlled trial was conducted in which female distressed individuals were randomized to three groups: (1) once-weekly yoga classes (12 sessions of 90 min in three months), (2) twice-weekly yoga classes (24 sessions of 90 min in three months), and (3) waiting list control.
The study is based on the results of a previous pilot study [
After signing an informed consent and collection of baseline data, subjects were randomized to moderate yoga (group 1 = once weekly 90 min yoga class for 3 months;
All subjects were asked to complete standardized questionnaires at the outset of the study (baseline), and after 3 months. The primary outcome was change of the mean score of the Cohen Perceived Stress Scale (CPSS) asking for subjective stress within the last week. The CPSS consists of 14 items about current levels of experienced and perceived stress [
Secondary outcomes included the following: the German Version of the Spielberger State-Trait Anxiety Inventory (STAI), which consists of 20 items relating to state anxiety and 20 items relating to trait anxiety [ the German translation of the Profile of Mood States (POMS) [ the German version of the Brief Symptom Inventory (BSI), which includes 53 items and provides scores for 9 psychological symptom scales and a general severity index (GSI) [ the German version of the Center for Epidemiological Studies Depression Inventory (CES-D), a 20-item scale designed for the general population [ quality of life (QOL) was measured by the German version of the Medical Outcomes Study 36-Item-Short Form (SF-36) with its 8 dimensions of health: physical functioning (10 items), social functioning (2 items), role limitations due to physical problems (4 items), role limitations due to emotional problems (3 items), mental health (5 items), energy/vitality (4 items), pain (2 items), and general health perception (5 items) and the physical and mental sum score; the Bf-S Zerssen well being scale measures momentary emotional well being and consists of three answer categories, with higher scores indicating lower well being [
In addition, we measured general physical well being and symptoms and severity of headache, neck, and back pain, using 10-point Likert scales for each category, with a reference period of the past week. Finally, general and specific physical complaints were measured with the well-validated, 70-item Freiburg Somatic Complaints (FBL) Questionnaire, that inventories subjective evaluation of physical complaints across the major physiological functional domains [
Participants in the yoga groups were asked to participate in once- or twice-weekly 90 min yoga classes according to the Iyengar style [
Patients were randomly allocated to a treatment group by a nonstratified block randomization with varying block lengths and by prepared sealed, sequentially numbered opaque envelopes containing the treatment assignments. Randomization was based on the “RANUNI” pseudo-random number generator of the SAS/Base statistical software (SAS Inc., Cary, NC, USA), and the envelopes were prepared by the study biostatistician. When a patient fulfilled all enrolment criteria, the study physician opened the lowest numbered envelope to reveal that patient’s assignment.
Sample size calculation was based on the results of the pilot study [
Outcomes were analysed on an intention-to-treat (ITT) basis by univariate analyses of covariance (ANCOVA) which included group and baseline values as well as outcome expectation as covariates. From these models we estimated baseline-adjusted treatment effects and their 95% confidence intervals (CI). ANCOVA was also used for ordinal data derived from the Likert scales. All reported
The primary analysis compared the outcomes between the 3 groups. Due to the compromised adherence in the yoga classes, we conducted secondary analyses in which the yoga groups were pooled and outcomes were analysed according to yoga class adherence. Here, participants were stratified according to the number of visits of yoga classes: 1–6 (
238 subjects responded to the advertisement. About 25 individuals declined participation, citing unavailability because of scheduling problems, time demands, travel requirements, or unspecified reasons. A total of 72 subjects fulfilled all entry criteria and were enrolled into the study. Subjects were recruited between March 2006 and January 2008 and were randomly allocated to the yoga group 1 (
Trial flow chart.
Two participants in the control group and 4 subjects in each yoga group dropped out due to causes not related to the study intervention, for example, unwillingness to stay in the study or return to the study center, lack of time, and minor medical problems (common cold).
Subjects’ ages ranged from 19 to 52 years (mean age
Baseline characteristics. Mean ± SD if not indicated otherwise.
Characteristic | Yoga group 1 ( |
Yoga group 2 ( |
Control group ( |
|
---|---|---|---|---|
Mean age, y | 39.5 ± 7.8 | 40.0 ± 8 | 39.3 ± 9.2 | 0.991 |
BMI (kg/m²) | 25.61 ± 3.7 | 25.7 ± 6 | 24.7 ± 6 | 0.357 |
Smokers, |
2 (8.3) | 9 (37.5) | 8 (33.3) | 0.046 |
Weight, kg | 74.4 ± 13.7 | 70.4 ± 18.5 | 70.8 ± 18.2 | 0.139 |
Exercise practice |
15 (62.5) | 7 (29.2) | 15 (62.5) | 0.028 |
Insomnia, |
19 (79.2) | 18 (75) | 21 (87.5) | 0.813 |
CPSS score | 34.0 ± 8.0 | 35.8 ± 6.3 | 31.2 ± 6.8 | 0.067 |
CES-D score | 22.3 ± 8.4 | 23.0 ± 8.1 | 21.0 ± 8.8 | 0.598 |
S-STAI | 45.5 ± 10.6 | 49.0 ± 9.3 | 43.5 ± 11.0 | 0.169 |
T-STAI | 53.6 ± 10.7 | 53.7 ± 9.1 | 50.2 ± 8.6 | 0.51 |
Bf-S | 24.9 ± 14.1 | 23.8 ± 13.8 | 23.5 ± 14.0 | 0.948 |
GSI-score | 67.6 ± 9.8 | 67.9 ± 7.2 | 67.4 ± 9.0 | 0.991 |
POMS vigor | 2.2 ± 0.8 | 2.2 ± 1.1 | 2.8 ± 1.3 | 0.194 |
POMS fatigue | 2.8 ± 1.5 | 2.5 ± 1.3 | 2.7 ± 1.4 | 0.613 |
POMS depression | 1.6 ± 1.5 | 1.1 ± 0.8 | 1.5 ± 1.2 | 0.649 |
POMS anger | 1.5 ± 1.6 | 1.0 ± 1.2 | 1.4 ± 1.3 | 0.418 |
QOL mental health | −0.8 ± 0.8 | −0.6 ± 0.8 | −0.7 ± 0.9 | 0.575 |
QOL physical score | 0.0 ± 0.8 | −0.1 ± 0.7 | −0.3 ± 0.8 | 0.542 |
QOL mental score | −1.7 ± 0.9 | −2.0 ± 0.7 | −1.6 ± 0.8 | 0.143 |
Freiburg complaint list | 2.7 ± 0.5 | 2.7 ± 0.5 | 2.6 ± 0.6 | 0.578 |
CPSS: Cohen Perceived Stress Scale; CES-D: Center for Epidemiological Studies Depression Scale; S-STAI: State Anxiety; T-STAI: Trait Anxiety; Bf-S: Zerssen well being scale; GSI: General Severity Index; POMS: Profile of Mood States; QOL: short form-36 Quality of Life.
Adherence to the yoga classes was moderate, with participants of yoga group 1 visiting
Both yoga programs were beneficial with regard to the course of perceived stress while the control group showed no relevant changes (Figure
Between-group differences of treatment effects on perceived stress and psychological outcomes, mean (95% CI).
Yoga group 1 versus control | Yoga group 2 versus control | Yoga group 1 + 2 versus control | ||||
---|---|---|---|---|---|---|
Change |
|
Change |
|
Change |
| |
CPSS | −6.7 (−10.9; −2.5) | 0.002 | −4.7 (−9.2; −0.3) | 0.036 | −5.7 (−9.5; −2.0) | 0.003 |
CES-D | −4.2 (−7.9; −0.5) | 0.028 | −4.6 (−8.5; −0.7) | 0.02 | −4.4 (−7.6; −1.2) | 0.008 |
S-STAI | −5.2 (−10.6; 0.1) | 0.056 | −6.0 (−11.6; −0.4) | 0.037 | −5.6 (−10.4; −0.9) | 0.021 |
T-STAI | −5.8 (−10.1; −1.6) | 0.007 | −5.3 (−9.5; −1.1) | 0.014 | −5.6 (−9.2; −1.9) | 0.003 |
GSI-score | −7.5 (−12.9; −2.2) | 0.006 | −8.2 (−13.5; −3.0) | 0.002 | −7.9 (−12.5; −3.3) | 0.001 |
Bf-S | −7.0 (−14.2; 0.2) | 0.057 | −6.2 (−13.3; 0.9) | 0.087 | −6.6 (−12.8; −0.4) | 0.036 |
POMS vigor | 0.8 (0.1; 1.4) | 0.022 | 0.6 (0.0; 1.3) | 0.06 | 0.7 (0.1; 1.3) | 0.017 |
POMS fatigue | −1.3 (−2.1; −0.6) | 0.001 | −1.0 (−1.8; −0.3) | 0.009 | −1.2 (−1.8; −0.5) | 0.001 |
POMS depression | −0.4 (−1.0; 0.2) | 0.20 | −0.3 (−0.9; 0.2) | 0.239 | −0.4 (−0.9; 0.1) | 0.154 |
POMS anger | −0.8 (−1.3; −0.2) | 0.007 | −0.5 (−1.1; 0.1) | 0.084 | −0.6 (−1.1; −0.1) | 0.012 |
QOL mental health | 0.8 (0.3; 1.3) | 0.002 | 0.6 (0.1; 1.1) | 0.022 | 0.7 (0.2; 1.1) | 0.002 |
QOL physical sum score | 0.1 (−0.3; 0.4) | 0.72 | −0.2 (−0.6; 0.2) | 0.269 | −0.1 (−0.4; 0.2) | 0.653 |
QOL mental sum score | 0.6 (0.1; 1.2) | 0.024 | 0.6 (0.0; 1.1) | 0.044 | 0.6 (0.1; 1.1) | 0.012 |
CPSS: Cohen Perceived Stress Scale; CES-D: Center for Epidemiological Studies Depression Scale; S-STAI: State Anxiety; T-STAI: Trait Anxiety; Bf-S: Zerssen well being scale; GSI: General Severity Index; POMS: Profile of Mood States; QOL: short form-36 Quality of Life.
Perceived stress. Mean (±SD) CPSS score on study entry and at three months in the yoga and control groups. Significant between-group treatment effect of −6.7 (−10.9; −2.5) (adj., 95% CI),
Both yoga intensities were similarly effective for most predefined secondary outcomes.
Results on psychological outcomes are summarized in Table
Comparing both pooled yoga interventions to controls, the psychological outcomes as state and trait anxiety, the GSI-score, the CES-D depression score, well being, and three dimensions of the POMS (vigor, fatigue, and anger) were better with yoga.
Mean changes in self-rated values of severity of general physical well being, neck and back pain (all Likert scaled), and the summarized complaint list score of the FBL are given in Table
Between-group differences of treatment effects on physical symptoms and complaints (when present), mean (95% CI).
Yoga group 1 versus control | Yoga group 2 versus control | Yoga group 1 + 2 versus control | ||||
---|---|---|---|---|---|---|
Change |
|
Change |
|
Change |
| |
Physical well being | −2.3 (−3.4; −1.0) | 0.001 | −0.7 (−2.0; 0.5) | 0.256 | −1.5 (−2.5; −0.4) | 0.007 |
Back pain | −1.7 (−3.1; −0.2) | 0.025 | −2.5 (−4.2; −0.8) | 0.004 | −2.1 (−3.5; −0.7) | 0.004 |
Neck pain | −2.2 (−3.6; −0.7) | 0.003 | −1.4 (−2.9; 0.1) | 0.06 | −1.8 (−3.1; −0.5) | 0.005 |
Freiburg complaint list, sum score | −0.3 (−0.5; −0.1) | 0.006 | −0.2 (−0.4; 0.0) | 0.115 | −0.2 (−0.4; 0.0) | 0.012 |
Also, outcomes for the pooled yoga groups on the 6 subscales of the FBL showed significant improvements compared to controls (data not shown in tables): tenseness (
As comparison between both yoga groups revealed no relevant group differences while adherence was better in yoga group 1 compared to yoga group 2, we conducted a further analysis to identify potential dose effects of yoga practice independent of group allocation.
Here, we found group-independent dose effects for back pain severity, the GSI-Score, the CES-D depression score, and state-trait anxiety (Table
Group differences for group-independent effects of yoga according to frequency of visited yoga classes compared to controls, mean (95% CI).
7–12 versus 0 yoga classes | 13–24 versus 0 yoga classes* | |||
---|---|---|---|---|
Change |
|
Change |
| |
Back pain | −2.3 (−3.7; −1.0) | 0.001 | −3.5 (−5.5; −1.5) | 0.001 |
GSI-Score | −8.5 (−13.9; −3.0) | 0.003 | −10.2 (−15.9; −4.4) | 0.001 |
CES-D | −4.5 (−8.3; −0.6) | 0.049 | −5.9 (−10.5; −1.3) | 0.011 |
S-STAI | −6.5 (−12.0; −1.0) | 0.02 | −7.4 (−13.4; −1.4) | 0.015 |
T-STAI | −6.1 (−10.5; −1.7) | 0.006 | −6.5 (−11.2; −1.8) | 0.007 |
GSI: General Severity Index; CES-D: Center for Epidemiological Studies Depression Scale; S-STAI: state anxiety; T-STAI: Trait Anxiety.
*Group differences between 7–12 and 13–24 classes not significant.
There were no clinically relevant adverse effects associated with yoga practice for all subjects.
We conducted this 3-armed randomized controlled trial with distressed women to investigate the effects of 2 different intensities of Iyengar yoga practice for 3 months on perceived stress and related psychological and physical outcomes. Compared to controls, women who participated in the yoga practice groups demonstrated pronounced and significant improvements in perceived stress and most related psychological and physical outcome measures. In contrast to our hypothesis, yoga classes twice a week were no more effective than a yoga class visit once a week; however, lower compliance in the intensified yoga group reduced the difference in yoga intensity between the two yoga groups. Nevertheless, in a separate analysis of the impact of yoga intensity independent of group allocation some dose effects were found for back pain, the GSI-Score, depression, and anxiety.
Baseline scores of perceived stress and depression and anxiety scores indicated the studied population having clinically relevant distress on study entry. Despite randomization of subjects, there were a number of significantly different baseline characteristics, including smoking and exercise habits. These differences were adjusted in the data analysis.
This trial adds further evidence for the use of Iyengar yoga as an effective stress reduction tool. We replicated the findings of our previous nonrandomized controlled pilot study [
A recent systematic review has looked at the ability of yoga to reduce stress levels in healthy adult populations and was based on eight trials that indicated a positive effect of yoga in reducing stress levels or stress symptoms [
Our current study had multiple strengths including the use of recommended and validated assessment tools and outcome measures, the high-quality yoga teaching, well-defined inclusion and exclusion criteria, an observation period of 3 months, and the comparison of two yoga intensities.
Nevertheless, the study has limitations, including modest sample sizes and no long-term followup. Furthermore, as with all studies with self-applied nonpharmacological interventions, it was impossible to blind treatments. We cannot estimate the extent to which the observed yoga effects were nonspecific due to the influence of setting, the attention of yoga teachers, the participants’ beliefs about the health-related effects of yoga and meaning responses [
A final possible limitation of this study relates to recruitment of self-described distressed women for a study in which the primary purpose was to evaluate the effects of B.K.S. Iyengar yoga on stress reduction. Admittedly, enrollment of subjects who rated themselves as “distressed,” but otherwise healthy, was subjective. Yet, this limitation is arguable, as baseline data from multiple validated instruments for stress assessment indicated that the women enrolled were, indeed, distressed.
Adherence to the yoga classes was worse than anticipated, especially in the group that was offered yoga twice weekly. The reduction of adherence started within the first weeks of the offered yoga classes. One may speculate that for the addressed study population with high demands in work and family life practicing yoga twice weekly for 90 min in distant centers might be not feasible in daily life. As our results indicate that once-weekly participation in yoga led to pronounced and clinically relevant improvements in outcomes, adhering to a more rigorous yoga practice schedule may be not necessary for stress-symptom improvement. On the other hand, the actual difference between the 2 yoga groups was one 90 min yoga session per week. Thus, we do not know if a more intensive yoga practice with 3 or 4 weekly classes would lead to more beneficial effects.
Various aspects of the yoga intervention could account for the observed beneficial effects on stress, mood, and well being. The yoga classes were activating through their vigorous postures, and participants may have experienced increasing feelings of mastery over time, as they were challenged to learn difficult postures. In addition, the commitment of an extra amount of time to concentrated practice might induce beneficial effects on self-control and foster self-efficacy. The practice of Iyengar yoga comprises physical movements with isometric muscle strengthening, stretching, and flexibility, combined with a mental focus and an emphasis on mindfulness of body movements and consideration of breathing patterns [
In conclusion, this study suggests that Iyengar yoga is an effective treatment for women in reducing mental distress and concomitant psychological and physical symptoms. Offering twice-weekly yoga classes is not superior to weekly classes. To better evaluate the impact of yoga on prevention and treatment of stress and stress-related disease, further studies are needed, which include longer-term followup, men, larger sample sizes, and control groups engaged in activity.
The authors do not have any conflict of interests with the content of the paper.
The study was supported by the Karl and Veronica Carstens Foundation, Essen.