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Sleep duration tied to dementia, death in Japanese older adults

Short and long daily sleep duration, as well as hypnotic use, are risk factors for dementia and death in Japanese older adults, according to findings published in the Journal of the American Geriatrics Society.

“The influence of sleep duration on development of dementia has not been fully investigated in Asian populations,” Tomoyuki Ohara, MD, PhD, department of neuropsychiatry, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan, and colleagues wrote. “Several epidemiological studies have revealed a U-shaped association between self-reported daily sleep duration and cognitive impairment, although some prospective studies conducted in Western populations have reported inconsistent results on the association between daily sleep duration and risk of dementia and its subtypes.”

Researchers examined the link between self-reported daily sleep duration and dementia and mortality risk in community-dwelling adults aged 60 years and older without dementia enrolled in a population-based prospective cohort study in Hisayama, Japan.

They also assessed whether use of benzodiazepines or psychotropic drugs for insomnia affected dementia and mortality risk in this population. Using a self-administered questionnaire, the investigators grouped participants into categories based on their daily sleep duration: less than 5 hours per day, 5 to 6.9 hours, 7 to 7.9 hours, 8 to 9.9 hours, 10 hours or more. Participants were followed for up to 10 years.

Overall, 294 participants developed dementia and 282 died during the follow-up period. After adjusting for age and sex, analysis revealed significantly higher incidence rates of dementia and all-cause mortality in older adults who reported sleeping less than 5 hours per day and 10 hours or more per day compared with those who reported daily sleep duration of 5 to 6.9 hours.

These associations stayed the same when adjusting for other confounders in those who reported daily sleep duration of less than 5 hours (HR = 2.64 [95% CI, 1.38-5.05] for dementia; HR = 2.29, [95% CI, 1.15-4.56] for death) and in those who reported 10 hours or more (HR = 2.23 [95% CI, 1.42-3.49] for dementia; HR = 1.67 [95% CI, 1.07-2.6] for death), according to the authors. Moreover, Ohara and colleagues saw similar U-shaped associations for Alzheimer’s disease and vascular dementia.

In addition, the results showed that older adults who used hypnotics and had any sleep duration were 1.66 times more at risk for developing dementia and 1.83 times more at risk for mortality compared with those who did not report hypnotic use and reported 5 to 6.9 hours of sleep per day.

When examining subgroups with high and low physical activity, researchers found participants with low physical activity who slept less than 5 hours or 10 or more hours per day had significantly greater risks of all-cause dementia and mortality than those who slept 5 to 6.9 hours. Among participants with high physical activity, the risk for all-cause dementia was only higher in those who slept 10 hours or more, not in those with a daily sleep duration of less than 5 hours. Furthermore, there was no significant link between daily sleep duration and risk for all-cause mortality in older adults with high physical activity.

“The present data constitute the first prospective finding that subjects with short and long sleep duration were at greater risk of developing dementia and its subtypes in a general population of Japanese elderly,” Ohara and colleagues wrote. “Given the beneficial effects of physical activity on risk of sleep disturbance, these findings indicate that not only maintenance of appropriate sleep duration, but also modification of lifestyle behaviors related to sleep (eg, obtaining adequate physical activity before using hypnotics) may be an effective strategy for preventing dementia and premature death in elderly adults.” – by Savannah Demko

Disclosures: The authors report no relevant financial disclosures.