Association of Sleep Disturbances with the Development of Cognitive Impairment: A Systematic Review

Abstract

Study objectives:In 2015 the existence of a "Glymphatic" system in the brain was proposed and further confirmed by subsequent studies. This system is supposed to drain brain waste metabolites particularly during sleep, when it has been shown to increase its activity by about 90%. This system may slow its activity with advancing years; furthermore, in patients with sleep disturbance or Obstructive Sleep Apnoea (OSA) it could be significantly reduced. This systematic review aims to estimate the association of sleep disturbances and OSA with the development of cognitive impairment or dementia. Methods:We searched PubMed, EMBASE, and PsycINFO up to July 2021 for observational comparative studies. Patients with sleep disorders, including OSA, were considered. Mild and severe cognitive impairment or dementia was chosen as outcomes. Risk of bias was evaluated by validated checklists. Results were described narratively. Results:Of 1794 studies identified by the search, 39 were included (14 longitudinal and 25 cross-sectional studies). Twelve longitudinal studies assessed the association between sleep disturbance and cognitive impairment, while five assessed the association between OSA and cognitive impairment. All studies except two, which assessed the impact of sleep disturbance, showed a positive association with cognitive impairment or dementia. Four out of five studies that assessed the impact of OSA also found a positive association with the incidence of cognitive impairment or dementia. Follow-up ranged from 1 to 17 years. Conclusions:Patients affected by sleep disturbance and sleep apnoea may have an increased risk of developing cognitive impairment or dementia in the following years.