Is sleeping more than 9 hours linked to later dementia?

Details

The study evaluated the association between sleep duration, the risk of developing dementia, and brain aging. In the Framingham Heart Study, 2,457 participants (mean age 72 ± 6 years; 57% women) reported their total sleep hours. Researchers grouped sleep as short (<6 hours), reference (6–9 hours), or long (>9 hours), and examined its association with incident dementia over 10 years and, cross-sectionally, with total cerebral brain volume (TCBV) and cognitive performance.

There were 234 cases of all-cause dementia during 10 years of follow-up. In multivariable analyses, prolonged sleep was associated with increased risk of incident dementia (hazard ratio [HR] 2.01; 95% confidence interval [CI] 1.24–3.26). The findings were driven by participants with mild cognitive impairment at baseline (HR 2.83; 95% CI 1.06–7.55) and those without a high school degree (HR 6.05; 95% CI 3.00–12.18).

Transitioning to more than 9 hours of sleep over an average of 13 years before baseline was associated with increased risk of all-cause dementia (HR 2.43; 95% CI 1.44–4.11) and clinical Alzheimer disease (HR 2.20; 95% CI 1.17–4.13). Compared with 6–9 hours of sleep, long sleep was also associated cross-sectionally with smaller TCBV (β ± SE, −1.08 ± 0.41 mean units of TCBV difference) and poorer executive function (β ± SE, −0.41 ± 0.13 SD units of Trail Making Test B minus A score difference).

The researchers concluded that prolonged sleep may be a marker of early neurodegeneration and a useful clinical tool for identifying people at higher risk of progressing to clinical dementia within 10 years.