Short daytime napping reduces the risk of cognitive decline in community-dwelling older adults: a 5-year longitudinal study.

BACKGROUND: Beneficial effects of napping on cognition have been suggested in cross-sectional studies. This study aimed to clarify longitudinal associations between cognitive decline and sleep characteristics, particularly daytime napping, over a 5-year period in older adults. METHODS: Study participants were 389 community-dwelling individuals aged ≥65 years living in Ojiya City, Niigata, Japan. Baseline and follow-up examinations were conducted in 2011-2013 and 2016-2018, respectively. Trained nurses visited and interviewed participants to collect the following information at baseline and follow-up: demographic characteristics, disease history, lifestyle habits including bedtime, sleeping hours, and daytime nap duration, and cognitive function. The assessment of cognitive function was performed using the revised Hasegawa's dementia scale (HDS-R), with cognitive decline defined as a change in the HDS-R of ≤ - 3 over 5 years. Odds ratios (ORs) for cognitive decline were calculated using multiple logistic regression analysis. RESULTS: Mean age of participants was 74.6 years (SD 6.4), and the cumulative incidence of cognitive decline was 106/389 (27.3%). The adjusted OR for 1-29 min daytime napping was significantly lower compared to that for no napping (OR = 0.47, 95%CI: 0.23-0.96). Earlier bedtime was associated with cognitive decline (adjusted P for trend = 0.0480). CONCLUSION: Short daytime napping (< 30 min) reduces the risk of cognitive decline over 5 years for community-dwelling older people. A future study will be necessary to confirm the effect of short napping on the reduction of risk for clinically diagnosed dementia.

Rural-urban differences in the prevalence of cognitive impairment in independent community-dwelling elderly residents of Ojiya city, Niigata Prefecture, Japan.

BACKGROUND: This study aimed to examine rural-urban differences in the prevalence of cognitive impairment in Japan. METHODS: We targeted 592 residents aged 65 years and older who did not use long-term care insurance services in one rural and two urban areas in Ojiya City, Japan. Of these, 537 (90.7 %) participated in the study. The revised Hasegawa's dementia scale (HDS-R) was used to assess cognitive function, and cognitive impairment was defined as a HDS-R score ≤20. Lifestyle information was obtained through interviews. The prevalence of cognitive impairment was compared according to the levels of predictor variables by odds ratios (ORs) calculated by a logistic regression analysis. RESULTS: Mean age of participants was 75.7 years (SD 7.0). The prevalence of cognitive impairment was 20/239 (8.4 %) in the rural area and 6/298 (2.0 %) in the urban areas, for a total of 26/537 (4.8 %) overall. Men tended to have a higher prevalence of cognitive impairment (P = 0.0628), and age was associated with cognitive impairment (P for trend <0.0001). The rural area had a significantly higher prevalence of cognitive impairment (age- and sex-adjusted OR = 4.04, 95 % CI: 1.54-10.62) than urban areas. This difference was significant after adjusting for other lifestyle factors. CONCLUSIONS: The prevalence of cognitive impairment was higher in the rural area relative to urban areas in Ojiya city. This regional difference suggests the existence of potentially modifiable factors other than lifestyle in relation to cognitive impairment.