A UK cohort study suggested that irregular sleep may represent a novel dementia risk factor. A random selection of 88,094 individuals (mean age 62 years, 56% women, and median sleep regularity index [SRI] 60) from a UK cohort was done between February 2013 and December 2015. The SRI was calculated as the probability of being in the same state (asleep/awake) at any 2 time points 24 hours apart, averaged over 7 days of accelerometry. There were 480 cases of incident dementia over a median 7.2 years of follow-up. Adjusted for demographic, clinical, and genetic confounders (APOE ε4), there was a nonlinear association between the SRI and dementia hazard with hazard ratios (HRs) following a U-shape pattern. HRs, relative to the median SRI, were 1.53 for participants with SRI at the 5th percentile (SRI = 41) and 1.16 for those with SRI at the 95th percentile (SRI = 71). In a subset with brain MRI (n = 15,263), gray matter and hippocampal volume tended to be lowest at the extremes of the SRI. The findings suggest that associations between sleep regularity and dementia are independent of sleep quality and duration, and both extremes of the SRI are linked to adverse brain health outcomes. It is well-known that both short and long sleep durations are tied to higher dementia risk. Source: https://www.neurology.org
