Are sleep disturbances modifiable risk factors for mild cognitive impairment and dementia? A systematic review of large studies.

Studies have shown a connection between sleep disorders, mild cognitive impairment and dementia. In this context, the present systematic review aimed to determine in large studies whether sleep disturbances are modifiable risk factors for cognitive decline. Following the application of inclusion and exclusion criteria, this systematic review selected 15 studies, with large cohort of subjects included (more than 1000 participants), who were longitudinally observed. Studies predominantly used questionnaires and interviews to collect subjective data on sleep. Eleven studies were based on subjective measurements, one was based on the International Classification of Diseases - 9th Edition diagnosis codes, and three based on objective actigraphic measurements. No study used polysomnographic assessments for the evaluation of sleep disorders.The results of this systematic review showed that extreme sleep durations (either too short or too long), daytime sleepiness, circadian sleep-wake cycle disruption, and variation in sleep patterns are factors associated with an increased risk of developing cognitive decline and dementia. Actigraphy, as an objective instrument for monitoring the sleep-wake rhythm, provided further insights into the association between sleep problems and longitudinal cognitive decline. These findings emphasize the strong connection between sleep disturbances, circadian rhythm, and the risk of developing dementia and Alzheimer's disease (AD). Sleep disorders may serve as an early indicator for cognitive decline, also considering that they may represent a modifiable risk factor for dementia. Therefore, recognition and treatment of sleep problems should be included in the prevention strategies against cognitive decline, opening up new opportunities for the prevention and treatment of cognitive impairment and AD.