Going to bed early, sleeping more than 8 hours may increase the risk

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A new study finds a rather surprising link between sleep patterns and dementia risk. André Rocha/EyeEm/Getty Images
  • New research suggests that bedtime and time in bed (TIB) may influence their risk of developing dementia.
  • Even in those who did not develop dementia, long BIR was associated with greater cognitive decline in people aged 60 to 74 and men.
  • Researchers suggest monitoring cognitive function in older adults with long BIR or early bedtimes as a potential risk factor for dementia.

China has the world’s largest population of people with dementia, a neurodegenerative disease. At least 6% of seniorsor one in 20 people aged 60 or over lives with dementia.

However, most studies of sleep and cognitive impairment have focused on Caucasian populations in North America and Europe.

A recent population-based study of elderly people in rural areas of China linked prolonged sleep and early sleep time with an increased risk of dementia.

The study also found that even among those who did not develop dementia during the study period, there was still some cognitive decline associated with prolonged sleep and early bedtimes. However, this particular finding was only evident in people aged 60 to 74 and men.

This clinical investigation appears in the Journal of the American Geriatrics Society.

Sleep is a complex biological process. Age-related changes in sleep duration and quality are associated with cognitive impairment.

Medical News Today discussed this study with Dr. Verna Porter, neurologist and director of dementia, Alzheimer’s disease and neurocognitive disorders at Providence Saint John’s Health Center in Santa Monica, California, who was not involved in the research current.

“It is important that studies assess populations other than white (Caucasian), predominantly urban populations in North America or Western Europe. This study assesses rural adults in China […] with unique socio-economic, cultural, educational and lifestyle practices,” said Dr Porter.

The elderly in rural China generally go to bed earlier, get up earlier and having poor quality sleep than their white counterparts or those living in urban areas.

To research shows that dementia occurs more often in rural areas of the country than in its developed parts.

The objective of the present study was to “examine the associations between self-reported sleep characteristics (eg, TIB, sleep duration, sleep duration, sleep quality, and EDS) with incident dementia, dementia (AD) and cognitive decline, while considering their potential interactions with demographic characteristics and APOE genotype.

The current cohort study recruited participants from the Shandong Yanggu Aging and Dementia Study, which involved rural elderly people in the western province of Shandong.

Over several months in 2014, researchers conducted clinical examinations, in-person interviews, and laboratory tests on 3,274 subjects aged 60 and older.

A total of 1,982 survivors from this reference group participated in a follow-up examination in 2018. Scientists studied sleep patterns at baseline and at follow-up.

They noted features such as:

  • BIT
  • bedtime
  • half-sleep time (the median between bedtime and waking time, to represent the circadian phase)
  • sleep latency (time in minutes it takes to fall asleep at night)
  • sleep efficiency (the proportion of time spent sleeping in bed)

The study authors used the Mini-Mental State Exam (MMSE) to measure cognitive function. They used criteria from the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) to diagnose dementia.

Next, the researchers recorded the results of a statistical model adjusted for age, sex and education.

They used another model to adjust for body mass index, smoking, alcohol consumption, diabetes, cardiovascular disease, and APOE genotype.

During the study’s average follow-up period of 3.7 years, 97 of 1,982 participants were diagnosed with dementia.

The average age of participants at baseline was 70.05 years. Women made up 59.6% of the sample, 83% were between 60 and 74 years old, and 38.2% of the subjects had no formal education.

The risk of dementia was 69% higher for people who slept more than 8 hours, compared to 7 to 8 hours. The risk was also twice as high for those who went to bed before 9 p.m., compared to 10 p.m. or later.

Among those who did not develop dementia during the study, baseline long BIR, early and mid-sleep time to bed, and early and late rise time measures were ‘significantly associated’ to a greater reduction in cognitive decline, as evidenced by MMSE scores.

Additionally, while dementia outcomes were the same across different demographic groups, changes in cognitive decline in people without dementia were only evident in people aged 60-74, but not in older subjects. 75 and over.

Similarly, the study found that early and late rise times corresponded to a greater drop in MMSE score in men, but not in women.

Dr. Porter offered possible reasons for the higher risk of cognitive decline in men:

“Cultural expectations [regarding] traditional gender roles, and [their] impact on work choice and socio-economic engagement, may potentially affect men differently in rural areas of China given their frequent role as primary “breadwinner” and their traditional engagement in more demanding employment physically and potentially stressful.

DTM also discussed this study with Dr. Michal Schnaider-Beeri, professor of psychiatry and director of the Sagol Neuroscience Research Center at Mount Sinai School of Medicine’s Sheba Medical Center in New York City.

Dr. Beeri noticed the strong association of sleep with cognitive decline in men. “Certain sleep disorders such as sleep apnea, [which is] prevalent among men, could be part of the explanation,” she said.

However, as Dr. Porter pointed out DTM that the study did not address the presence or absence of sleep apnea.

Dr. Beeri was impressed with the broad scope of the study in covering sleep issues. Its unique population, large sample size, and adjustment for factors such as age, gender, education, etc. did a solid job of it, she said.

The results do not show causation, however. For example, researchers could not pinpoint the exact reasons for age-related differences with cognitive decline. Gender differences in cognitive outcomes are still “poorly understood”.

The study also did not take into account mood-related symptoms or daytime naps, which are common among older people in rural China.

Another limitation of this study is the use of self-report, which carries potential for recall bias. Multiple testing could have produced false positive associations, the study authors noted.

Because the study participants came from only one region of China, the researchers urged caution when generalizing the findings to other populations.

Also, Dr. Porter mentioned that the follow-up period was short.

The authors of the study hope that their findings “may partly fill the knowledge gap” about people with low socioeconomic status.

They say their findings should encourage monitoring of older adults “who report prolonged TIB and advanced sleep patterns, particularly in older adults. [ages] 60-74 years and men.

Future work could explore how reducing TIB and adjusting sleep duration could delay the onset of cognitive decline and dementia.

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