To the Editor
Malek-Ahmadi et al. [1] evaluated the association between self-reported sleep duration and cognitive impairment in 189 cognitively normal older adults. Adjusted odds ratio (95 % confidence interval) of short sleep duration (≤7 h) against long sleep duration (≥ 9h) for cognitive impairment was 0.86 (0.76–0.98). The authors concluded that old subjects with long sleep duration had a risk of decreased cognitive performance. I have two comments on their study.
First, Chen et al. [2] reported the association between self-reported sleep duration and cognitive decline or mild cognitive impairment (MCI)/dementia in older women. Although they concluded that both short and long sleep duration had a risk for cognitive decline and MCI/dementia, adjusted hazard ratio of short sleep duration against normal sleep duration for MCI/dementia only showed statistical significance. Although Chen et al. presented some biological mechanisms on the association between short sleep duration and MCI/dementia in older women, further study is needed to confirm the association.
Second, the authors used self-reported sleep duration, and sleep evaluation methods should be handled with caution for the risk assessment of cognitive decline or MCI/dementia [3, 4]. Deterioration of sleep was predominantly progressed by psychological distress, and causal association between sleep loss and subsequent cognitive decline or MCI/dementia would be mediated not only by depression but also anxiety [5]. In addition, classification of self-reported short (long) sleep duration needs validation study. Furthermore, Malek-Ahmadi et al. handled cognitively normal older adults. Taken together, the association between sleep duration and cognitive impairment should be evaluated by a cohort or intervention study to confirm the causal association .
References
Malek-Ahmadi M, Kora K, O’Connor K et al (2016) Longer self-reported sleep duration is associated with decreased performance on the montreal cognitive assessment in older adults. Aging Clin Exp Res 28:333–337
Chen JC, Espeland MA, Brunner RL et al (2016) Sleep duration, cognitive decline, and dementia risk in older women. Alzheimers Dement 12:21–33
Almondes KM, Costa MV, Malloy-Diniz LF et al (2016) Insomnia and risk of dementia in older adults: systematic review and meta-analysis. J Psychiatr Res 77:109–115
Guarnieri B, Sorbi S (2015) Sleep and cognitive decline: a strong bidirectional relationship. It is time for specific recommendations on routine assessment and the management of sleep disorders in patients with mild cognitive impairment and dementia. Eur Neurol 74:43–48
Orgeta V, Qazi A, Spector A et al (2015) Psychological treatments for depression and anxiety in dementia and mild cognitive impairment: systematic review and meta-analysis. Br J Psychiatry 207:293–298
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Kawada, T. Sleep duration and cognitive impairment in older adults. Aging Clin Exp Res 29, 817 (2017). https://doi.org/10.1007/s40520-016-0631-5
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DOI: https://doi.org/10.1007/s40520-016-0631-5