Long sleep duration linked to rapid cognitive decline
Prolonged duration of sleep is associated with a higher risk of cognitive decline among patients with mild cognitive impairment (MCI) and early Alzheimer’s disease (AD), according to a study presented at the Singapore Health & Biomedical Congress (SHBC) 2018.
“Sleep duration alone can be a potential marker [for affected] cognition, given its plausible biological mechanisms,” said study lead author Dr Pauline Seah from Tan Tock Seng Hospital in Singapore.
This prospective cohort study analysed 105 patients (mean age 77 years) with MCI or early AD who visited the memory clinic at Tan Tock Seng Hospital in Singapore between 2014 and 2017. Global Pittsburgh Sleep Quality Index (PSQI) score was used to assess the baseline sleep quality for a month before the study. Clinical Dementia Rating Sum of Boxes (CDR-SB) score, ranging from 0 (none) to 3 (severe), was used to measure cognitive performance at 12 months. Patients with cognitive decline were categorized as rapid progressors (defined as CDR-SB score of ≥2; 28.6 percent) or non-rapid progressors (71.4 percent). [SHBC 2018]
Patients who were rapid progressors had a significantly longer sleep duration compared with non-rapid progressors (8.07 vs 6.79 hours; p=0.004).
After adjusting for potential confounders, longer sleep duration was associated with a rapid cognitive decline (odds ratio, 1.42, 95 percent confidence interval, 1.07–1.89; p=0.02).
A good sleep quality was observed in both rapid and non-rapid progressors, as shown by a lower global PSQI score (mean, 3.90 vs 4.83; p=0.219), although this was not significant.
The researchers acknowledged that the study had several limitations, such as the lack of information on sleep disorders, daytime sleeping patterns, and any intervening events within 12 months.
“Apart from sleep duration, various sleep disorders or changes in sleep architecture may also impact cognitive impairment,” Seah said, who also added that “our findings support the utility of sleep assessment as a clinical tool in predicting risk of cognitive decline.”
“Further studies are required to elucidate the relationship between excessive sleep and dementia progression including,” she added.