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Letter by Kawada Regarding Article, “Sleep Duration and Risk of Stroke Mortality Among Chinese Adults: Singapore Chinese Health Study”
To the Editor: Pan et al1 conducted a follow-up study for the effect of sleep duration on the stroke mortality, with a subanalysis based on the type of stroke. Both short (≤5 hours per day) and long (≥9 hours per day) sleep durations were associated with a significant increase in the risk of ischemic or unspecified stroke. In addition, a history of hypertension also significantly contributed to the stroke mortality, irrespective of the sleep duration. I have 2 concerns about their study. First, a systematic review and meta-analysis has been reported for the effect of sleep duration on the incidence rate of cardiovascular diseases, including stroke,2 which indicated a significant association between both short and long durations of sleep and the incidence of stroke. Pan et al1 conducted their stroke mortality study with a satisfactory number of samples and a sufficiently long follow-up period. If possible, the effect of sleep duration on the incidence of stroke should also be considered in their study. I suppose that the subanalysis based on the types of stroke represents useful information. Second, I agree with the comments of the authors that the impact of poor sleep quality on the risk of cardiovascular disease has been poorly studied. However, appropriate sleep duration differs from person to person, and there is no standard or reference value for sleep duration to predict human health. I think that sleep duration does not fully reflect sleep quality,3,4 and I recommend that Pan et al1 consider inclusion of other sleep variables such as the existence of insomnia and sleep medication to confirm the association between sleep quality and stroke.
Puttonen et al5 presented a model pathway that job stress such as shift work may trigger psychological overload and behavioral changes of life, including sleep quality and length of sleep. I speculate that sleep duration and vascular events are not directly related and that many physical and mental factors are confounders of this association. Although sleep is an important lifestyle factor, the direction of causality should be determined by further studies.
Disclosures None.
Tomoyuki Kawada Department of Hygiene and Public Health Nippon Medical School Tokyo, Japan 1. Pan A, De Silva DA, Yuan JM, Koh WP. Sleep duration and risk of stroke mortality among Chinese adults: Singapore Chinese Health Study. Stroke. 2014;45:1620–1625. 2. Cappuccio FP, Cooper D, D’Elia L, Strazzullo P, Miller MA. Sleep duration predicts cardiovascular outcomes: a systematic review and metaanalysis of prospective studies. Eur Heart J. 2011;32:1484–1492. 3. Kawada T. Quality of sleep, sleep duration and depressive state. J Clin Hypertens (Greenwich). 2012;14:479. 4. Dowd JB, Goldman N, Weinstein M. Sleep duration, sleep quality, and biomarkers of inflammation in a Taiwanese population. Ann Epidemiol. 2011;21:799–806. 5. Puttonen S, Härmä M, Hublin C. Shift work and cardiovascular disease - pathways from circadian stress to morbidity. Scand J Work Environ Health. 2010;36:96–108.
(Stroke. 2014;45:e134.) © 2014 American Heart Association, Inc. Stroke is available at http://stroke.ahajournals.org
DOI: 10.1161/STROKEAHA.114.006002
Downloaded from http://stroke.ahajournals.org/ e134 at Monash University on June 4, 2015
Letter by Kawada Regarding Article, ''Sleep Duration and Risk of Stroke Mortality Among Chinese Adults: Singapore Chinese Health Study'' Tomoyuki Kawada Stroke. 2014;45:e134; originally published online June 10, 2014; doi: 10.1161/STROKEAHA.114.006002 Stroke is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 2014 American Heart Association, Inc. All rights reserved. Print ISSN: 0039-2499. Online ISSN: 1524-4628
The online version of this article, along with updated information and services, is located on the World Wide Web at: http://stroke.ahajournals.org/content/45/7/e134
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Stroke can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. Once the online version of the published article for which permission is being requested is located, click Request Permissions in the middle column of the Web page under Services. Further information about this process is available in the Permissions and Rights Question and Answer document. Reprints: Information about reprints can be found online at: http://www.lww.com/reprints Subscriptions: Information about subscribing to Stroke is online at: http://stroke.ahajournals.org//subscriptions/
Downloaded from http://stroke.ahajournals.org/ at Monash University on June 4, 2015
Letter by Kawada Regarding Article, “Sleep Duration and Risk of Stroke Mortality Among Chinese Adults: Singapore Chinese Health Study”
To the Editor: Pan et al1 conducted a follow-up study for the effect of sleep duration on the stroke mortality, with a subanalysis based on the type of stroke. Both short (≤5 hours per day) and long (≥9 hours per day) sleep durations were associated with a significant increase in the risk of ischemic or unspecified stroke. In addition, a history of hypertension also significantly contributed to the stroke mortality, irrespective of the sleep duration. I have 2 concerns about their study. First, a systematic review and meta-analysis has been reported for the effect of sleep duration on the incidence rate of cardiovascular diseases, including stroke,2 which indicated a significant association between both short and long durations of sleep and the incidence of stroke. Pan et al1 conducted their stroke mortality study with a satisfactory number of samples and a sufficiently long follow-up period. If possible, the effect of sleep duration on the incidence of stroke should also be considered in their study. I suppose that the subanalysis based on the types of stroke represents useful information. Second, I agree with the comments of the authors that the impact of poor sleep quality on the risk of cardiovascular disease has been poorly studied. However, appropriate sleep duration differs from person to person, and there is no standard or reference value for sleep duration to predict human health. I think that sleep duration does not fully reflect sleep quality,3,4 and I recommend that Pan et al1 consider inclusion of other sleep variables such as the existence of insomnia and sleep medication to confirm the association between sleep quality and stroke.
Puttonen et al5 presented a model pathway that job stress such as shift work may trigger psychological overload and behavioral changes of life, including sleep quality and length of sleep. I speculate that sleep duration and vascular events are not directly related and that many physical and mental factors are confounders of this association. Although sleep is an important lifestyle factor, the direction of causality should be determined by further studies.
Disclosures None.
Tomoyuki Kawada Department of Hygiene and Public Health Nippon Medical School Tokyo, Japan 1. Pan A, De Silva DA, Yuan JM, Koh WP. Sleep duration and risk of stroke mortality among Chinese adults: Singapore Chinese Health Study. Stroke. 2014;45:1620–1625. 2. Cappuccio FP, Cooper D, D’Elia L, Strazzullo P, Miller MA. Sleep duration predicts cardiovascular outcomes: a systematic review and metaanalysis of prospective studies. Eur Heart J. 2011;32:1484–1492. 3. Kawada T. Quality of sleep, sleep duration and depressive state. J Clin Hypertens (Greenwich). 2012;14:479. 4. Dowd JB, Goldman N, Weinstein M. Sleep duration, sleep quality, and biomarkers of inflammation in a Taiwanese population. Ann Epidemiol. 2011;21:799–806. 5. Puttonen S, Härmä M, Hublin C. Shift work and cardiovascular disease - pathways from circadian stress to morbidity. Scand J Work Environ Health. 2010;36:96–108.
(Stroke. 2014;45:e134.) © 2014 American Heart Association, Inc. Stroke is available at http://stroke.ahajournals.org
DOI: 10.1161/STROKEAHA.114.006002
Downloaded from http://stroke.ahajournals.org/ e134 at Monash University on June 4, 2015
Letter by Kawada Regarding Article, ''Sleep Duration and Risk of Stroke Mortality Among Chinese Adults: Singapore Chinese Health Study'' Tomoyuki Kawada Stroke. 2014;45:e134; originally published online June 10, 2014; doi: 10.1161/STROKEAHA.114.006002 Stroke is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 2014 American Heart Association, Inc. All rights reserved. Print ISSN: 0039-2499. Online ISSN: 1524-4628
The online version of this article, along with updated information and services, is located on the World Wide Web at: http://stroke.ahajournals.org/content/45/7/e134
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Stroke can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. Once the online version of the published article for which permission is being requested is located, click Request Permissions in the middle column of the Web page under Services. Further information about this process is available in the Permissions and Rights Question and Answer document. Reprints: Information about reprints can be found online at: http://www.lww.com/reprints Subscriptions: Information about subscribing to Stroke is online at: http://stroke.ahajournals.org//subscriptions/
Downloaded from http://stroke.ahajournals.org/ at Monash University on June 4, 2015
