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Sleep duration, sleep quality and coronary heart disease mortality
International Journal of Cardiology 223 (2016) 534–535
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Correspondence
Sleep duration, sleep quality and coronary heart disease mortality☆,☆☆ Linn B. Strand a, Min Kuang Tsai b,c, David Gunnell d, Imre Janszky a,e, Chi Pang Wen c,f,⁎, Shu-Sen Chang g,⁎⁎ a
Department of Public Health and General Practice, Norwegian University of Science and Technology, Hakon Jarls gate 11, 7495 Trondheim, Norway Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, No 17, Xu-Zhou Road, Taipei City 10055, Taiwan c Institute of Population Health Science, National Health Research Institutes, 35 Keyan Road, Zhunan Town, Miaoli County 350, Taiwan d School of Social and Community Medicine, University of Bristol, 39 Whatley Road, Bristol BS8 2PS, United Kingdom e Regional center for health care improvement, St Olav Hospital, Prinsesse Kristinas gate 3, 7030 Trondheim, Norway f China Medical University Hospital, 91 Hsueh-Shih Road, Taichung 40402, Taiwan g Institute of Health Behaviors and Community Sciences and Department of Public Health, College of Public Health, National Taiwan University, No 17, Xu-Zhou Road, Taipei City 10055, Taiwan b
a r t i c l e
i n f o
Article history: Received 8 July 2016 Accepted 5 August 2016 Available online 09 August 2016 Keywords: Sleep Coronary heart disease Cardiovascular disease Sleep duration Sleep quality
We read Dr. Kawada's commentary [1] on our article [2] with great interest, and we value his thoughts and suggestions for moving this field forward. Although our data showed statistical evidence for an association of short sleep duration (0–4 h) with coronary heart disease (CHD) only among females and in those aged 65 years or older, there was a trend towards increased risk in short sleepers in the whole sample (hazard ratio [HR] = 1.36, 95% confidence interval [CI] 0.88–2.10). Additionally, we examined the quadratic relationship which showed statistical evidence for a U-shaped relationship between sleep duration and CHD mortality in the complete sample (p for quadratic trend = 0.011). Thus, we think it is appropriate to report a U-shaped relationship in this instance. Our findings that this U-shaped relationship was stronger in females and in those aged 65 years or older is novel, and we agree that future studies should further examine this. Furthermore, it is
☆ Statement of authorship: “This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation”. ☆☆ Grant support: Linn B. Strand received a research fellowship grant from the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. ⁎ Correspondence to: C. P. Wen, China Medical University Hospital, 91 Hsueh-Shih Road, Taichung 40402, Taiwan. ⁎⁎ Correspondence to: S.-S. Chang, College of Public Health, National Taiwan University, No 17, Xu-Zhou Road, Taipei City 10055, Taiwan. E-mail addresses: [email protected] (C.P. Wen), [email protected] (S.-S. Chang).
http://dx.doi.org/10.1016/j.ijcard.2016.08.119 0167-5273/© 2016 Published by Elsevier Ireland Ltd.
important to be cautious about assuming causality from observational data. We agree that not only sleep duration, but also sleep quality and other sleep parameters are potentially important. In addition to the question about sleep duration, the participants in the health check were also asked the question; “How have you slept in the past month?”—there were five response categories: (a) I had difficulties falling asleep, (b) I had no problem falling asleep, but was easily awoken, (c) I dreamt a lot, (d) I needed sleeping pills and (e) I slept well. We have now additionally examined the association of the sleep problems with CHD mortality using Cox proportional hazards models on the same sample as in the original paper [2]. We have included the results from the analysis of the sleep problems below (Table 1). Our data showed no evidence for an association of self-reported sleep problems at baseline with CHD mortality; although a selfreported need for sleeping pills was associated with 54% increased risk in the sex- and age-adjusted model, the strength of the association was attenuated and its statistical evidence limited in the fully adjusted model (HR = 1.35, 95% CI 0.90–2.03). This analysis was limited by a relatively small number of deaths in the ‘need sleeping pills’ group (n = 32), and that sleep problems were measured only once at baseline by self-report. Furthermore, participants were instructed to choose only one response to the sleep problem question and thus the analysis was limited in identifying individuals with multiple and severe sleep problems. In regard to the categorization of sleep duration, the National Sleep Foundation in the United States has recommended normal sleep duration as ‘7–9 h’ for healthy adults aged between 26 and 64 years and ‘7–8 h’ for those aged 65 years or older based on expert consensus which involved 18 panelists, assisted by a systematic review of literature which identified 312 relevant articles [3]. Participants in the health check were given only four response options to describe their sleep duration (0–4, 4–6, 6–8 or N8 h per night), so we had a limited choice of reference categories. We chose 6–8 h as the reference category in our models because it a) included most of the recommended sleep periods and b) was the most commonly reported sleep duration, leading to more precise estimates of risk in the other sleep duration categories. Future research could contribute to the evidence base of any recommendations or guidelines by categorizing sleep duration consistent with the recommendations / guidelines, but this was not an option in our study.
L.B. Strand et al. / International Journal of Cardiology 223 (2016) 534–535
535
Table 1 Hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of sleep problems with coronary heart disease (CHD) mortality in the MJ health check-up programme, Taiwan (N = 392 164) Model 1
Sleep problems None Difficult getting to sleep Easily awoken Dreamed a lot Need sleeping pills
Model 2
Model 3
Cases
Person-years
HR
95% CI
HR
95% CI
HR
95% CI
273 110 222 74 32
1 435 948 450 958 1 187 236 626 806 50 740
1.00 1.13 0.91 0.79 1.54
0.90, 1.41 0.77, 1.09 0.61, 1.02 1.07, 2.23
1.00 0.99 0.90 0.75 1.16
0.79, 1.24 0.76, 1.08 0.58, 0.97 0.80, 1.69
1.00 1.01 0.91 0.78 1.35
0.80, 1.26 0.76, 1.09 0.60, 1.01 0.90, 2.03
Model 1: adjusted for age and sex. Model 2: adjusted for age, sex, education and marital status, smoking, alcohol consumption, physical activity, history of hypertension, history of diabetes and history of heart diseases. Model 3: adjusted for age, sex, education, marital status, smoking, alcohol consumption, physical activity, history of hypertension, history of diabetes, history of heart disease, body mass index, systolic blood pressure, fasting glucose, total cholesterol, HDL cholesterol, triglycerides and use of hypnotics/sedatives.
Conflict of interest The author reports no relationships that could be construed as a conflict of interest Acknowledgments Linn B. Strand received a research fellowship grant from the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. David Gunnell's time is supported by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care West (CLAHRC West) at University Hospitals Bristol NHS Foundation Trust. The views expressed are those of the authors and not necessarily those of the NHS, NIHR or Department of Health. Grant support: Taiwan Ministry of Health and Welfare Clinical Trial and Research Center of Excellence (MOHW104-TDU-B-212-113002), China Medical University
Hospital. The funding source had no role in study design, data collection, data analysis, data interpretation, writing of the report, or in the decision to submit the paper for publication. Raw data used for analysis in this research were received from MJ Health Resource Center (Authorization Code: MJHRFB2014001C). The MJ Health Resource Foundation is responsible for the data distribution.
References [1] T. Kawada, Sleep duration and coronary heart disease mortality, Int. J. Cardiol. 215 (2016) 110. [2] L.B. Strand, M.K. Tsai, D. Gunnell, I. Janszky, C.P. Wen, S.-S. Chang, Self-reported sleep duration and coronary heart disease mortality: a large cohort study of 400,000 Taiwanese adults, Int. J. Cardiol. 207 (2016) 246–251. [3] M. Hirshkowitz, K. Whiton, S.M. Albert, C. Alessi, O. Bruni, L. DonCarlos, et al., National Sleep Foundation's sleep time duration recommendations: methodology and results summary, Sleep Health 1 (1) (2015) 40–43.
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Correspondence
Sleep duration, sleep quality and coronary heart disease mortality☆,☆☆ Linn B. Strand a, Min Kuang Tsai b,c, David Gunnell d, Imre Janszky a,e, Chi Pang Wen c,f,⁎, Shu-Sen Chang g,⁎⁎ a
Department of Public Health and General Practice, Norwegian University of Science and Technology, Hakon Jarls gate 11, 7495 Trondheim, Norway Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, No 17, Xu-Zhou Road, Taipei City 10055, Taiwan c Institute of Population Health Science, National Health Research Institutes, 35 Keyan Road, Zhunan Town, Miaoli County 350, Taiwan d School of Social and Community Medicine, University of Bristol, 39 Whatley Road, Bristol BS8 2PS, United Kingdom e Regional center for health care improvement, St Olav Hospital, Prinsesse Kristinas gate 3, 7030 Trondheim, Norway f China Medical University Hospital, 91 Hsueh-Shih Road, Taichung 40402, Taiwan g Institute of Health Behaviors and Community Sciences and Department of Public Health, College of Public Health, National Taiwan University, No 17, Xu-Zhou Road, Taipei City 10055, Taiwan b
a r t i c l e
i n f o
Article history: Received 8 July 2016 Accepted 5 August 2016 Available online 09 August 2016 Keywords: Sleep Coronary heart disease Cardiovascular disease Sleep duration Sleep quality
We read Dr. Kawada's commentary [1] on our article [2] with great interest, and we value his thoughts and suggestions for moving this field forward. Although our data showed statistical evidence for an association of short sleep duration (0–4 h) with coronary heart disease (CHD) only among females and in those aged 65 years or older, there was a trend towards increased risk in short sleepers in the whole sample (hazard ratio [HR] = 1.36, 95% confidence interval [CI] 0.88–2.10). Additionally, we examined the quadratic relationship which showed statistical evidence for a U-shaped relationship between sleep duration and CHD mortality in the complete sample (p for quadratic trend = 0.011). Thus, we think it is appropriate to report a U-shaped relationship in this instance. Our findings that this U-shaped relationship was stronger in females and in those aged 65 years or older is novel, and we agree that future studies should further examine this. Furthermore, it is
☆ Statement of authorship: “This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation”. ☆☆ Grant support: Linn B. Strand received a research fellowship grant from the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. ⁎ Correspondence to: C. P. Wen, China Medical University Hospital, 91 Hsueh-Shih Road, Taichung 40402, Taiwan. ⁎⁎ Correspondence to: S.-S. Chang, College of Public Health, National Taiwan University, No 17, Xu-Zhou Road, Taipei City 10055, Taiwan. E-mail addresses: [email protected] (C.P. Wen), [email protected] (S.-S. Chang).
http://dx.doi.org/10.1016/j.ijcard.2016.08.119 0167-5273/© 2016 Published by Elsevier Ireland Ltd.
important to be cautious about assuming causality from observational data. We agree that not only sleep duration, but also sleep quality and other sleep parameters are potentially important. In addition to the question about sleep duration, the participants in the health check were also asked the question; “How have you slept in the past month?”—there were five response categories: (a) I had difficulties falling asleep, (b) I had no problem falling asleep, but was easily awoken, (c) I dreamt a lot, (d) I needed sleeping pills and (e) I slept well. We have now additionally examined the association of the sleep problems with CHD mortality using Cox proportional hazards models on the same sample as in the original paper [2]. We have included the results from the analysis of the sleep problems below (Table 1). Our data showed no evidence for an association of self-reported sleep problems at baseline with CHD mortality; although a selfreported need for sleeping pills was associated with 54% increased risk in the sex- and age-adjusted model, the strength of the association was attenuated and its statistical evidence limited in the fully adjusted model (HR = 1.35, 95% CI 0.90–2.03). This analysis was limited by a relatively small number of deaths in the ‘need sleeping pills’ group (n = 32), and that sleep problems were measured only once at baseline by self-report. Furthermore, participants were instructed to choose only one response to the sleep problem question and thus the analysis was limited in identifying individuals with multiple and severe sleep problems. In regard to the categorization of sleep duration, the National Sleep Foundation in the United States has recommended normal sleep duration as ‘7–9 h’ for healthy adults aged between 26 and 64 years and ‘7–8 h’ for those aged 65 years or older based on expert consensus which involved 18 panelists, assisted by a systematic review of literature which identified 312 relevant articles [3]. Participants in the health check were given only four response options to describe their sleep duration (0–4, 4–6, 6–8 or N8 h per night), so we had a limited choice of reference categories. We chose 6–8 h as the reference category in our models because it a) included most of the recommended sleep periods and b) was the most commonly reported sleep duration, leading to more precise estimates of risk in the other sleep duration categories. Future research could contribute to the evidence base of any recommendations or guidelines by categorizing sleep duration consistent with the recommendations / guidelines, but this was not an option in our study.
L.B. Strand et al. / International Journal of Cardiology 223 (2016) 534–535
535
Table 1 Hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of sleep problems with coronary heart disease (CHD) mortality in the MJ health check-up programme, Taiwan (N = 392 164) Model 1
Sleep problems None Difficult getting to sleep Easily awoken Dreamed a lot Need sleeping pills
Model 2
Model 3
Cases
Person-years
HR
95% CI
HR
95% CI
HR
95% CI
273 110 222 74 32
1 435 948 450 958 1 187 236 626 806 50 740
1.00 1.13 0.91 0.79 1.54
0.90, 1.41 0.77, 1.09 0.61, 1.02 1.07, 2.23
1.00 0.99 0.90 0.75 1.16
0.79, 1.24 0.76, 1.08 0.58, 0.97 0.80, 1.69
1.00 1.01 0.91 0.78 1.35
0.80, 1.26 0.76, 1.09 0.60, 1.01 0.90, 2.03
Model 1: adjusted for age and sex. Model 2: adjusted for age, sex, education and marital status, smoking, alcohol consumption, physical activity, history of hypertension, history of diabetes and history of heart diseases. Model 3: adjusted for age, sex, education, marital status, smoking, alcohol consumption, physical activity, history of hypertension, history of diabetes, history of heart disease, body mass index, systolic blood pressure, fasting glucose, total cholesterol, HDL cholesterol, triglycerides and use of hypnotics/sedatives.
Conflict of interest The author reports no relationships that could be construed as a conflict of interest Acknowledgments Linn B. Strand received a research fellowship grant from the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. David Gunnell's time is supported by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care West (CLAHRC West) at University Hospitals Bristol NHS Foundation Trust. The views expressed are those of the authors and not necessarily those of the NHS, NIHR or Department of Health. Grant support: Taiwan Ministry of Health and Welfare Clinical Trial and Research Center of Excellence (MOHW104-TDU-B-212-113002), China Medical University
Hospital. The funding source had no role in study design, data collection, data analysis, data interpretation, writing of the report, or in the decision to submit the paper for publication. Raw data used for analysis in this research were received from MJ Health Resource Center (Authorization Code: MJHRFB2014001C). The MJ Health Resource Foundation is responsible for the data distribution.
References [1] T. Kawada, Sleep duration and coronary heart disease mortality, Int. J. Cardiol. 215 (2016) 110. [2] L.B. Strand, M.K. Tsai, D. Gunnell, I. Janszky, C.P. Wen, S.-S. Chang, Self-reported sleep duration and coronary heart disease mortality: a large cohort study of 400,000 Taiwanese adults, Int. J. Cardiol. 207 (2016) 246–251. [3] M. Hirshkowitz, K. Whiton, S.M. Albert, C. Alessi, O. Bruni, L. DonCarlos, et al., National Sleep Foundation's sleep time duration recommendations: methodology and results summary, Sleep Health 1 (1) (2015) 40–43.