Researchers have determined in a new study that diverse sleep disturbances markedly elevate the risk of cognitive decline and dementia, placing high value on the management of sleep as a prominent modifiable cause in brain preservation. This study reaffirmed that insufficient and excessive sleep, insomnia, and poor sleep quality are robust predictors of cognitive decline and dementia, including Alzheimer's disease (AD) and vascular dementia (VD). The study was published in theJournal of Neurologyby Jinhuan Z. and colleagues. The research team searched PubMed, EMBASE, and Web of Science databases systematically until February 18, 2025, for cohort studies that had investigated the longitudinal association of sleep disorders with cognitive impairment or dementia. There were 76 cohort studies found to be eligible, including eight categories of sleep disturbances. The aggregated data were used to calculate relative risks (RRs) for 95% confidence intervals (CIs) to examine associations between individual sleep issues and several cognitive outcomes. Sensitivity analysis was used to test robustness of findings, with Egger's and Begg's tests used to identify publication bias. Sources of heterogeneity between studies were examined with meta-regression analysis. The study uncovered that various types of sleep disturbances are strongly associated with higher risks of cognitive impairment and dementia. Insomnia was linked with a small but significant increase in risk of dementia (RR = 1.13). Both short sleep time (≤7 hours) and long sleep time (≥8 hours) were harmful short sleep was associated with a 27% greater risk (RR = 1.27), whereas long sleep was associated with a 23% greater risk of cognitive decline, 43% greater risk of all-cause dementia, and a 66% greater risk of Alzheimer's disease (RR = 1.66). In addition, excessive daytime sleepiness was found to be a very significant risk factor, with RR = 1.85 for vascular dementia, RR = 1.41 for all-cause dementia, and RR = 1.37 for cognitive decline. Sleep-related movement disorders had the most significant impact, with an increase in vascular dementia risk more than 2.5 times (RR = 2.53). Moreover, sleep quality was associated with increased risks of Alzheimer's disease (RR = 1.24), all-cause dementia (RR = 1.17), and cognitive decline (RR = 1.18). This large scale meta-analysis offers strong evidence that sleep disturbances are important independent risk factors for dementia and cognitive decline, especially Alzheimer's disease and vascular dementia. Sleep management should be given priority as a preventive strategy in clinical and community settings. By ensuring early detection and intervention for sleep disorders, clinicians can potentially reduce the increasingly large global burden of dementia and enhance overall cognitive health outcomes. Zhang, J., Ou, J., Lu, X. et al. Sleep disorders and the risk of cognitive decline or dementia: an updated systematic review and meta-analysis of longitudinal studies. J Neurol 272, 689 (2025).https://doi.org/10.1007/s00415-025-13372-x