Over a mean follow-up of 7.9 years, 694 incident dementia cases were recorded in a cohort of 82,391 adults.
A U-shaped association was observed between sleep duration and incident dementia, with short sleep (< 7 h) linked to a higher risk.
The median sleep duration for those sleeping less than 7 hours was 6.5 hours, associated with a hazard ratio of 1.19 for developing dementia.
Sleep regularity was negatively associated with dementia risk in a near-linear manner.
Participants with higher sleep regularity ( ≥ 70) had a hazard ratio of 0.74 for dementia compared to those with lower regularity (SRI < 70).
The beneficial effects of sleep regularity on dementia risk were noted primarily among individuals with short (< 7 h) and long (≥ 8 h) sleep durations.
Simplified
BACKGROUND: Sleep is a crucial lifestyle factor with impacts on mental and cognitive health. The associations between objectively measured sleep and risk of incident dementia are not yet fully understood. To evaluate the associations of device-measured sleep duration and regularity with incident dementia and explore whether sleep regularity moderates the association of sleep duration with dementia.
METHODS: Population-based prospective cohort study of 82,391 adults aged 43 to 79 years from the UK Biobank accelerometry subsample, collected between 2013 and 2015, followed up to 2022. Device-based sleep duration (h/day) and (SRI), a metric ranging from 0-100 that quantifies a person's sleep regularity (with a greater value indicating higher consistency), were calculated from wrist-worn accelerometry data recorded over the course of one week. Incident all-cause dementia cases were obtained from national hospital admission, primary care and mortality data followed up to 30 November 2022. We used Cox proportional hazard models to estimate the hazard ratios (HRs) for incident dementia after adjustment for common demographic and clinical covariates.
RESULTS: Over a mean follow-up of 7.9 years, 694 incident dementia cases occurred. We observed a U-shaped association between sleep duration and incident dementia, with only short sleep (< 7 h) being significantly associated with a higher risk of dementia. The median sleep duration for short sleepers (< 7 h) of 6.5 h, compared to the reference point of 7.9 h was associated with 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 (linear p = 0.01, non-linear p = 0.57). When we dichotomized sleep regularity, those in the higher sleep regularity group (SRI ≥ 70) had an HR of 0.74 (95%CI 0.63, 0.87) compared to those with lower sleep regularity (SRI < 70). The beneficial associations between sleep regularity and incident dementia were present only among participants with short (< 7 h) and long (≥ 8 h) sleep duration.
CONCLUSIONS: Assuming that the associations we observed are causal, maintaining a regular sleep pattern may help offset the deleterious association of inadequate sleep duration with dementia. Interventions aimed at improving sleep regularity may be a viable option for people not able to achieve the recommended hours of sleep.
Key numbers
1.19
Increase in Dementia Risk
Hazard ratio for incident dementia among those averaging 6.5 hours of sleep.
0.74
Lower Dementia Risk with Higher Regularity
Hazard ratio for dementia risk in those with ≥ 70 vs. < 70.
694
Participants with Short Sleep Duration
Total incident dementia cases over a mean follow-up of 7.9 years.
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Declarations. Ethics approval and consent to participate: The ethical approval was received from the UK National Health service (NHS) and National Research Ethics Service for the UK (No. 11/NW/0382) and participants provided written informed consent. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.
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