Existing evidence highlights associations between sleep behaviors and dementia risk; however, the impact of adhering to a healthy sleep pattern on dementia risk remains unclear.Of 406,364 UK Biobank participants aged 40-64, we excluded those who had withdrawn, had incomplete sleep data, or had dementia at baseline, yielding a final sample of 333,014. Participants were enrolled between 2006 and 2010, with follow-up extending from recruitment to dementia diagnosis, death, loss to follow-up, or the censoring date (December 2022), whichever came first. Incident dementia was identified using hospital inpatient and death records, along with primary care data, with cases diagnosed at a mean age of 70.0 years (standard deviation [SD]: 5.6). Sleep-related questionnaire items from the UK Biobank were summarized into five sleep behaviors: sleeping 7-8 h daily, early chronotype, absence of frequent insomnia, no snoring, and no frequent daytime sleepiness. Each behavior meeting the healthy criterion was assigned one point, resulting in a total range from 0 to 5, with higher scores indicating better adherence to a healthy sleep pattern. Cox proportional hazards models were used to assess the association between healthy sleep patterns and dementia risk, adjusting for demographics, lifestyle factors, and medical history. A subset of 33,401 participants underwent brain magnetic resonance imaging (MRI) scans during the 9.4-year median period between sleep assessment and imaging. The imaging analysis included total brain volume, gray matter volume, white matter volume, hippocampal volume, and white matter hyperintensities (WMH).During a median follow-up of 13.8 years, 3,035 incident dementia cases were recorded, including 1,304 Alzheimer's disease (AD) cases and 597 vascular dementia (VD) cases. A higher adherence to a healthy sleep pattern was associated with a lower dementia risk. Each 1-point increase in the healthy sleep score corresponded to a 7% reduction in dementia risk (Hazard Ratio [HR] = 0.93, 95% Confidence Interval [CI]: 0.89-0.96). Compared to participants with a score of 0-1, those with a score of 5 had a significantly lower risk of dementia (HR = 0.75, 95% CI: 0.61-0.92). Benefits were more pronounced in adults aged 40-55 years than those aged 56-64 years (p for interaction < 0.001). Adherence to a healthy sleep pattern was associated with increased grey matter volume and decreased WMH volume (all p < 0.05). Mediation analysis indicates that preserving grey and white matter integrity partially mediated the dementia-risk-lowering benefit (p < 0.05).Adherence to a healthy sleep pattern is associated with both a reduced risk of dementia and greater white matter integrity, underscoring the role of improving overall sleep behaviors to support brain structure and lower dementia risk.© 2025. The Author(s).