This study was conducted in China, which currently has the world’s oldest population, and at least 6% of those people over the age of 60 are living with dementia. This study involved 1,982 older adults who were enrolled in the Shandong Tanggu Study of Aging and Dementia in China and set out to investigate the associations between sleep timing, quality, and duration, with dementia.
Findings suggest that going to bed too early or sleeping too long increases the risk of dementia. According to the researchers, for those who slept longer than 8 hours the risk of dementia was 69% higher, and it was twice as high for those who went to sleep before 9 PM. Interestingly even for those who did not develop dementia, men who got out of bed too early or too late showed greater signs of cognitive decline, but this effect was not observed in women.
Aging-related changes in sleep timing and quality have previously been associated with cognitive disorders. Work-life can affect sleep timing, such as with older adults in rural China, who typically go to sleep earlier, get up earlier, and have a lower quality of sleep. Additional research shows that dementia can occur more often in rural regions than in developed parts.
Over a period of several months interviews, examinations, and testing were conducted on 3,274 subjects over the age of 60, a total of 1,982 survivors of this group participated in the follow-up 4 years later. Sleep patterns were examined from baseline to follow-up, noting the time spent in bed, bedtime, mid-sleep time, sleep latency, and sleep efficiency. The MMSE was used to measure cognitive function, using the DSM-IV criteria to diagnose dementia. A statistical model was used to adjust for factors such as education, age, and gender, then another model adjusted for BMI, smoking history, alcohol use, cardiovascular disease, APOE genotype, and diabetes.
97 of the 1,982 participants developed dementia during the average follow-up of 3.7 years. The risk of dementia was found to be 69% higher in those who slept for more than 8 hours compared to those sleeping for 7-8 hours, and the risk was twice as high for those going to sleep before 9 PM compared to those going to bed at 10 PM or later.
Among the participants who did not develop dementia the amount of time spent in bed, early bedtime and mid-time sleep, and early and late rise time metrics were significantly associated with a great reduction in cognitive decline. While the dementia results were the same among the different demographic groups, cognitive decline changes in those who remained dementia-free were only observed in those between the ages of 60-74 but not in those aged 75 or older. Additionally, early and late rise times corresponded with a greater MMSE score decline in men, but these results were not observed in women.
“Cultural expectations [regarding] traditional gender roles, and [their] impact on job choice and socioeconomic engagement, may potentially differentially affect men in rural China given their frequent role as the primary ‘breadwinner’ and their traditional engagement in more physically demanding and potentially stressful employment,” explained Dr. Verna Porter, a neurologist and director of the Dementia, Alzheimer’s Disease, and Neurocognitive Disorders at Providence Saint John’s Health Center in Santa Monica, CA, who was not involved in the current research.
“Certain sleep disturbances such as sleep apnea, [which is] prevalent in men, might be part of the explanation,” said Dr. Michal Schnaider-Beeri, director of the Joseph Sagol Center for Neuroscience Research at Sheba Medical Center in Ramat Gan, Israel, and professor of psychiatry at the Mount Sinai School of Medicine in New York.
This study was not without limitations such as using self-reporting, not addressing either the absence or presence of sleep apnea, not considering mood-related symptoms, not taking into account daytime napping, a short follow-up period, and participants only coming from one region in China among others.
The researchers hope that their findings can help partly bridge the knowledge gap regarding people with low socioeconomic status, and they encourage monitoring older adults who spend a prolonged amount of time in bed.
