Dose-response associations of device measured sleep regularity and duration with incident dementia in 82391 UK adults

Objectives: To evaluate the associations of device-measured sleep duration and regularity with incident dementia, and to explore whether regular sleep might mitigate any association of sleep duration with dementia. Methods: This population-based prospective cohort study of 82391 adults from the UK Biobank accelerometry subsample included adults aged 43 to 79 years old in England, Scotland, and Wales. Sleep duration (h/day) and Sleep Regularity Index (SRI, range 0-100) were calculated from the wrist-worn accelerometry data collected by participants over the course of one week. Cox proportional hazard models were used to estimate the hazard ratios (HRs) and assess the independent associations between sleep and incident dementia after adjustment for common demographic and contextual covariates. Results: Over a mean follow-up of 7.9 years, during which 694 incident dementia cases occurred, there was a U-shaped association between sleep duration and incident dementia. Short sleep (<7 h) was associated with increased dementia risk, while long sleep (≥ 8h) was not significantly associated with dementia risk. The median sleep duration for short sleepers (<7 h) of 6.5 hours was associated with an HR of 1.19 (95% CI 1.01, 1.40) for incident dementia. Sleep regularity was negatively associated with dementia risk in a near-linear fashion. The sample median SRI of approximately 73, compared to the reference point of 51, was associated with an HR of 0.76 (95%CI 0.61, 0.94). The SRI value where the risk reduction was 50% of the maximum observed of 66, was associated with an HR of 0.77 (95%CI 0.63, 0.95). Among individuals with sleep duration outside the optimal range (too short or too long), less regular sleep was associated with increased risk of dementia. Among those with optimal sleep duration (7-8h/day), there was no significant association between sleep regularity and dementia risk. Compared to the reference point (SRI: 51), an SRI value of 62 for non-optimal sleepers was associated with a 25% reduction in risk for dementia (HR: 0.75; 95% CI 0.63, 0.90). Conclusions: A regular sleep pattern may mitigate some adverse effects of inadequate sleep duration, suggesting that interventions aimed at improving sleep regularity may be a suitable option for people not able to achieve the recommended hours of sleep. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study is funded by an Australian National Health and Medical Research Council (NHMRC) Investigator Grant (APP1194510). The funder had no specific role in any of the following study aspects: the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: We used data from the UK Biobank cohort study that enrolled over 500,000 participants between 2006 and 2010 and informed written consent was provided [18]. The ethical approval was completed by the UK National Health service (NHS) and National Research Ethics Service for the UK (No. 11/NW/0382). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The data that support the findings of this study are available from UK Biobank http://www.ukbiobank.ac.uk/. Restrictions apply to the availability of these data, which were used under application number 25813, and so are not publicly available. Data are available from the authors upon reasonable request and with permission of the UK Biobank.