A new study suggests it's best not to go to bed too early or sleep too long to avoid a greater risk of dementia. Photo by Security/Pixabay
Sept. 21 (UPI) -- The time at which people go to bed and how long they sleep may affect their risk of developing dementia and cognitive decline, a new study suggests.
The results were published Wednesday in the Journal of the American Geriatrics Society.
A team of researchers from China, Sweden and the United Kingdom found a 69% higher risk of dementia in individuals who slept for more than eight hours, versus sleeping seven to eight hours, and a two-times higher risk for people drifting off before 9 p.m. versus 10 p.m. or later.
Moreover, the findings suggest "cognitive function should be monitored in older adults who report prolonged time in bed and advanced sleep timing, especially in older individuals aged 60 to 74 years and men," the research paper said.
Future research "may help clarify whether moderately reducing [time in bed] and delaying sleep timing can slow down cognitive decline and delay dementia onset on older adults," wrote Dr. Rui Liu, in the Department of Neurology at Shandong University's Shandong Provincial Hospital in Jinan, China, the study's lead author.
The study included roughly 2,000 older adults in China who were free of dementia at its start; 97 participants were diagnosed with dementia during an average follow-up period of 3.7 years.
The researchers underscored that most studies of sleep and dementia have been conducted among almost exclusively White populations in North America and Europe, and have failed to focus on rural older adults.
This is important because older adults living in rural parts of China, as compared to Western populations and city dwellers, "usually go to bed earlier, rise earlier, have poorer sleep and are more susceptible to dementia," attributable partly to differences in socioeconomic status, culture, education and lifestyle, the study said.
To try to bridge the knowledge gap, the study targeted rural-dwelling, older adults, mostly low-income and with limited education, in western Shandong Province.
The scientists noted that sleep problems and cognitive decline are known to be linked to demographics: age, sex and education. And, they said, a well-established genetic risk factor for dementia has been associated with short sleep duration.
Yet, to date, population-based studies have yielded mixed results about links between sleep problems and dementia, they said.
They acknowledged their own study's limitations, and said the results should be interpreted with caution, since sleep characteristics were self-reported, there was a lack of data on factors such as sleep apnea, and the period of follow-up monitoring was relatively short.