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.
Department of Hygiene and Public Health
Nippon Medical School
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- © 2014 American Heart Association, Inc.
- Pan A,
- De Silva DA,
- Yuan JM,
- Koh WP
- Cappuccio FP,
- Cooper D,
- D’Elia L,
- Strazzullo P,
- Miller MA