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Yoga participation and all-cause mortality: National prospective cohort study
Complementary Therapies in Medicine 23 (2015) 757–758
Contents lists available at ScienceDirect
Complementary Therapies in Medicine journal homepage: www.elsevierhealth.com/journals/ctim
Short communication
Yoga participation and all-cause mortality: National prospective cohort study Paul D. Loprinzi ∗ Center for Behavioral Research, Department of Health, Exercise Science, and Recreation Management, The University of Mississippi, 229 Turner Center, University, MS 38677, United States
a r t i c l e
i n f o
Article history: Received 14 June 2015 Received in revised form 21 July 2015 Accepted 6 August 2015 Available online 18 August 2015 Keywords: Epidemiology Mortality Survival
a b s t r a c t Background: The relatively few studies examining the effect of yoga participation on chronic disease come from small, short-term studies. As a result, the purpose of this study was to prospectively examine the effects of yoga participation on all-cause mortality in a large nationally representative study with a relatively long follow-up period (up to 12 year follow-up). Methods: Data from the 1999–2006 National Health & Nutrition Examination Survey were used, with follow-up through 2011. Yoga participation was self-reported, with participant identification linked to death certificate data from the National Death Index to ascertain mortality status. Results: In the analyzed sample, which included 22,598 adult participants, 240 participants engaged in yoga and 3176 died over the follow-up period; the median follow-up period was 102 months (8.5 years). In an unadjusted Cox hazard model, those engaging in yoga, compared to those not engaging in yoga, had a 63% reduced risk of premature all-cause mortality (HR = 0.37; 95% CI: 0.18–0.74; P = .006). However, after adjusting for age, the association was attenuated and no longer statistically significant (HRadjusted = 0.82; 95% CI: 0.39–1.72; P = .60). Conclusion: In conclusion, yoga participation was not significantly associated with reduced all-cause mortality risk in an adjusted model. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction With yoga serving as a type of physical activity and stress management strategy, growing evidence suggests that yoga may have beneficial effects on various ailments, such as hypertension1,2 and coronary artery disease.3,4 However, the findings at this point are relatively weak,4 and come from small, short-term studies.2,3 As a result, the purpose of this short report was to prospectively examine the effects of yoga participation on all-cause mortality in a large, nationally-representative study with a relatively long follow-up period (up to 12 years). 2. Methods 2.1. Design and participants The present study includes data from the 1999–2006 National Health and Nutrition Examination Survey (only cycles at the time of
∗ Fax: +1 662 915 5525. E-mail address: [email protected] http://dx.doi.org/10.1016/j.ctim.2015.08.004 0965-2299/© 2015 Elsevier Ltd. All rights reserved.
this writing with yoga participation data). Data from participants in these cycles were linked to death certificate data from the National Death Index. Person–months of follow-up were calculated from the date of the interview until date of death or censoring on December 31, 2011, whichever came first. Analyses are based on data from 22,598 adults (18–85 years) who provided complete data for the study variables. The NHANES is an ongoing survey conducted by the Centers for Disease Control and Prevention that uses a representative sample of non-institutionalized United States civilians selected by a complex, multistage, stratified, clustered probability design. The multistage design consists of 4 stages, including the identification of counties, segments (city blocks), random selection of households within the segments, and random selection of individuals within the households. Procedures were approved by the National Center for Health Statistics review board. Consent was obtained from all participants prior to data collection. Further information on NHANES methodology and data collection is available on the NHANES website (http:// www.cdc.gov/nchs/nhanes.htm).
758
P.D. Loprinzi / Complementary Therapies in Medicine 23 (2015) 757–758
2.2. Measurement of yoga
4. Discussion
Participants were asked if they engaged in moderate or vigorous-intensity yoga (lasting at least 10 min in duration) in the past 30 days. Among those participating in yoga, they were asked to report the number of times they engaged in yoga in the past 30 days and the average duration each time.
The main finding of this large, nationally-representative prospective cohort study was that the unadjusted model suggested a protective survival benefit among those engaging in yoga, but the results were no longer significant in an adjusted model. As a result, the findings of this brief report are in accordance with a recent review highlighting minimal effects of yoga on mortality, exercise capacity and health-related quality of life.4 This should not, however, diminish the potential health-related effects (e.g., reduced oxidative stress) of yoga in some vulnerable populations (e.g., hypertensive older adults), which has been demonstrated elsewhere.2 Notable strengths of this short report include the national prospective study and the relatively reasonable follow-up period. Given the relatively low engagement in yoga in this national sample (N = 240), future studies targeting individuals who actively participate in yoga are needed. It is possible that the relatively small number of participants engaging in yoga may have rendered inadequate statistical power to detect an association. However, an unadjusted association between yoga and mortality was observed. Like most prospective studies, another limitation is the single baseline assessment of yoga within the past 30 days. It is possible that yoga patterns could have changed during the follow-up period. Future prospective representative samples employing a larger sample of yoga participants and evaluating changes in yoga patterns are needed before strong conclusions can be made regarding the potential yoga-mortality relationship.
2.3. Analysis Statistical analyses were performed via procedures from survey data using Stata (v.12). To account for oversampling, non-response, non-coverage, and to provide nationally representative estimates, analyses included the use of survey sample weights, clustering and primary sampling units. Cox proportional hazard models were used to examine the association of yoga on all-cause mortality. Schoenfeld’s residuals were used to verify the proportional hazards assumption. The proportional hazards assumption was not violated (chi-square = 9.75, P = .13), with the Harrell’s C concordance statistic being 0.86. 3. Results In the analyzed sample of the 1999–2006 NHANES participants, which included 22,598 adult participants, 3176 died over the follow-up period (unweighted %, 14.05%; weighted %, 9.5%); the median follow-up period was 102 months (8.5 years), with the maximum follow-up period being 153 months (12.75 years). Among the 22,598 participants, 240 reported engaging in yoga within the past 30 days (unweighted %, 1.06%; weighted %, 1.5%). The unweighted mean (95% CI) number of times engaging in yoga in the past 30 days was 10.1 (7.4–12.7), with the unweighted mean duration being 46.4 min (43.1–49.6). In an unadjusted Cox hazard model, those engaging in yoga, compared to those not engaging in yoga, had a 63% reduced risk of premature all-cause mortality (HR = 0.37; 95% CI: 0.18–0.74; P = .006). However, after adjusting for age, the association was attenuated and no longer statistically significant (HRadjusted = 0.82; 95% CI: 0.39–1.72; P = .60). Similarly, when adjusting for age, gender and race-ethnicity, there was no association between yoga and allcause mortality (HRadjusted = 0.94; 95% CI: 0.45–1.94; P = .86). The inclusion of other covariates (e.g., education, smoking, overall physical activity, number of sessions of yoga in the past 30 days, etc.) did not alter the results.
Acknowledgement The author declares no conflict of interest and no funding was used to prepare this manuscript. References 1. Awdish R, Small B, Cajigas H. Development of a modified yoga program for pulmonary hypertension: a case series. Altern Ther Health Med. 2015;21:48–52. 2. Patil SG, Dhanakshirur GB, Aithala MR, Naregal G, Das KK. Effect of yoga on oxidative stress in elderly with grade-I hypertension: a randomized controlled study. J Clin Diagn Res. 2014;8:BC04–07. 3. Kwong JS, Lau HL, Yeung F, Chau PH, Woo J. Yoga for secondary prevention of coronary heart disease. Cochrane Database Syst Rev. 2015;6:CD009506. 4. Cramer H, Lauche R, Haller H, Dobos G, Michalsen A. A systematic review of yoga for heart disease. Eur J Prev Cardiol. 2015;22:284–295.
Contents lists available at ScienceDirect
Complementary Therapies in Medicine journal homepage: www.elsevierhealth.com/journals/ctim
Short communication
Yoga participation and all-cause mortality: National prospective cohort study Paul D. Loprinzi ∗ Center for Behavioral Research, Department of Health, Exercise Science, and Recreation Management, The University of Mississippi, 229 Turner Center, University, MS 38677, United States
a r t i c l e
i n f o
Article history: Received 14 June 2015 Received in revised form 21 July 2015 Accepted 6 August 2015 Available online 18 August 2015 Keywords: Epidemiology Mortality Survival
a b s t r a c t Background: The relatively few studies examining the effect of yoga participation on chronic disease come from small, short-term studies. As a result, the purpose of this study was to prospectively examine the effects of yoga participation on all-cause mortality in a large nationally representative study with a relatively long follow-up period (up to 12 year follow-up). Methods: Data from the 1999–2006 National Health & Nutrition Examination Survey were used, with follow-up through 2011. Yoga participation was self-reported, with participant identification linked to death certificate data from the National Death Index to ascertain mortality status. Results: In the analyzed sample, which included 22,598 adult participants, 240 participants engaged in yoga and 3176 died over the follow-up period; the median follow-up period was 102 months (8.5 years). In an unadjusted Cox hazard model, those engaging in yoga, compared to those not engaging in yoga, had a 63% reduced risk of premature all-cause mortality (HR = 0.37; 95% CI: 0.18–0.74; P = .006). However, after adjusting for age, the association was attenuated and no longer statistically significant (HRadjusted = 0.82; 95% CI: 0.39–1.72; P = .60). Conclusion: In conclusion, yoga participation was not significantly associated with reduced all-cause mortality risk in an adjusted model. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction With yoga serving as a type of physical activity and stress management strategy, growing evidence suggests that yoga may have beneficial effects on various ailments, such as hypertension1,2 and coronary artery disease.3,4 However, the findings at this point are relatively weak,4 and come from small, short-term studies.2,3 As a result, the purpose of this short report was to prospectively examine the effects of yoga participation on all-cause mortality in a large, nationally-representative study with a relatively long follow-up period (up to 12 years). 2. Methods 2.1. Design and participants The present study includes data from the 1999–2006 National Health and Nutrition Examination Survey (only cycles at the time of
∗ Fax: +1 662 915 5525. E-mail address: [email protected] http://dx.doi.org/10.1016/j.ctim.2015.08.004 0965-2299/© 2015 Elsevier Ltd. All rights reserved.
this writing with yoga participation data). Data from participants in these cycles were linked to death certificate data from the National Death Index. Person–months of follow-up were calculated from the date of the interview until date of death or censoring on December 31, 2011, whichever came first. Analyses are based on data from 22,598 adults (18–85 years) who provided complete data for the study variables. The NHANES is an ongoing survey conducted by the Centers for Disease Control and Prevention that uses a representative sample of non-institutionalized United States civilians selected by a complex, multistage, stratified, clustered probability design. The multistage design consists of 4 stages, including the identification of counties, segments (city blocks), random selection of households within the segments, and random selection of individuals within the households. Procedures were approved by the National Center for Health Statistics review board. Consent was obtained from all participants prior to data collection. Further information on NHANES methodology and data collection is available on the NHANES website (http:// www.cdc.gov/nchs/nhanes.htm).
758
P.D. Loprinzi / Complementary Therapies in Medicine 23 (2015) 757–758
2.2. Measurement of yoga
4. Discussion
Participants were asked if they engaged in moderate or vigorous-intensity yoga (lasting at least 10 min in duration) in the past 30 days. Among those participating in yoga, they were asked to report the number of times they engaged in yoga in the past 30 days and the average duration each time.
The main finding of this large, nationally-representative prospective cohort study was that the unadjusted model suggested a protective survival benefit among those engaging in yoga, but the results were no longer significant in an adjusted model. As a result, the findings of this brief report are in accordance with a recent review highlighting minimal effects of yoga on mortality, exercise capacity and health-related quality of life.4 This should not, however, diminish the potential health-related effects (e.g., reduced oxidative stress) of yoga in some vulnerable populations (e.g., hypertensive older adults), which has been demonstrated elsewhere.2 Notable strengths of this short report include the national prospective study and the relatively reasonable follow-up period. Given the relatively low engagement in yoga in this national sample (N = 240), future studies targeting individuals who actively participate in yoga are needed. It is possible that the relatively small number of participants engaging in yoga may have rendered inadequate statistical power to detect an association. However, an unadjusted association between yoga and mortality was observed. Like most prospective studies, another limitation is the single baseline assessment of yoga within the past 30 days. It is possible that yoga patterns could have changed during the follow-up period. Future prospective representative samples employing a larger sample of yoga participants and evaluating changes in yoga patterns are needed before strong conclusions can be made regarding the potential yoga-mortality relationship.
2.3. Analysis Statistical analyses were performed via procedures from survey data using Stata (v.12). To account for oversampling, non-response, non-coverage, and to provide nationally representative estimates, analyses included the use of survey sample weights, clustering and primary sampling units. Cox proportional hazard models were used to examine the association of yoga on all-cause mortality. Schoenfeld’s residuals were used to verify the proportional hazards assumption. The proportional hazards assumption was not violated (chi-square = 9.75, P = .13), with the Harrell’s C concordance statistic being 0.86. 3. Results In the analyzed sample of the 1999–2006 NHANES participants, which included 22,598 adult participants, 3176 died over the follow-up period (unweighted %, 14.05%; weighted %, 9.5%); the median follow-up period was 102 months (8.5 years), with the maximum follow-up period being 153 months (12.75 years). Among the 22,598 participants, 240 reported engaging in yoga within the past 30 days (unweighted %, 1.06%; weighted %, 1.5%). The unweighted mean (95% CI) number of times engaging in yoga in the past 30 days was 10.1 (7.4–12.7), with the unweighted mean duration being 46.4 min (43.1–49.6). In an unadjusted Cox hazard model, those engaging in yoga, compared to those not engaging in yoga, had a 63% reduced risk of premature all-cause mortality (HR = 0.37; 95% CI: 0.18–0.74; P = .006). However, after adjusting for age, the association was attenuated and no longer statistically significant (HRadjusted = 0.82; 95% CI: 0.39–1.72; P = .60). Similarly, when adjusting for age, gender and race-ethnicity, there was no association between yoga and allcause mortality (HRadjusted = 0.94; 95% CI: 0.45–1.94; P = .86). The inclusion of other covariates (e.g., education, smoking, overall physical activity, number of sessions of yoga in the past 30 days, etc.) did not alter the results.
Acknowledgement The author declares no conflict of interest and no funding was used to prepare this manuscript. References 1. Awdish R, Small B, Cajigas H. Development of a modified yoga program for pulmonary hypertension: a case series. Altern Ther Health Med. 2015;21:48–52. 2. Patil SG, Dhanakshirur GB, Aithala MR, Naregal G, Das KK. Effect of yoga on oxidative stress in elderly with grade-I hypertension: a randomized controlled study. J Clin Diagn Res. 2014;8:BC04–07. 3. Kwong JS, Lau HL, Yeung F, Chau PH, Woo J. Yoga for secondary prevention of coronary heart disease. Cochrane Database Syst Rev. 2015;6:CD009506. 4. Cramer H, Lauche R, Haller H, Dobos G, Michalsen A. A systematic review of yoga for heart disease. Eur J Prev Cardiol. 2015;22:284–295.