Joint association of daytime sleep behaviors and dietary quality with the risk of dementia: A large prospective cohort study

Background: Identifying modifiable risk factors of dementia is crucial for its early prevention. Daytime sleep behaviors (DSB) and diet are synergetic factors, both potentially important in maintaining cognitive health. However, whether they may jointly influence the risk of dementia in the general population remains unclear. Methods: This study included 187,078 participants from the UK Biobank. DSB burden (low, medium, and high) was assessed through two questions regarding daytime sleepiness and napping. The Recommended Food Score (RFS) was calculated to assess dietary quality (by tertile). We ascertained incident dementia through linkage to hospital inpatient records. We used Cox proportional hazards regression models to estimate the associations. Results: During a median follow-up of 10 years, we documented 1,351 cases with incident dementia. Compared with participants with low DSB burden, those with high DSB burden had a 21% (hazard ratio [HR]: 1.21; 95% confidence interval [CI]: 1.06, 1.38) higher risk of incident dementia. Dietary quality was negatively associated with dementia risk (HR for tertile 1 versus tertile 3: 1.42; 95% CI: 1.24, 1.63). There was a significant interaction between DSB burden and RFS (P for interaction = 0.027). Compared with participants with low DSB burden & high RFS, those with high DSB burden had higher risks of incident dementia, regardless of RFS level. Conclusions: High DSB burden and low dietary quality separately or in joint were significantly associated with higher risks of incident dementia, while high DSB burden seems to play a decisive role. Our findings imply that programs targeting the two behavioral factors, particularly the DSB, may help to prevent dementia.