Sleep matters: Poor sleep in your 30s can increase your dementia risk
Key Takeaways
Disrupted sleep in younger adulthood has been associated with midlife cognitive impairments.
Research about disrupted sleep and its effect on cognition is ongoing, but it’s widely recognized that quality sleep is a marker of good health.
It’s important to assess your patient’s sleep quality; monitoring and addressing sleep disturbances should be part of preventive care for cognitive decline.
Disrupted sleep in early adulthood may be linked to cognitive problems even a decade later, according to a new study published in Neurology.[]
About the study
Investigators studied 526 individuals (58% female, 44% Black, mean age: 40.1 ± 3.6 years at baseline). The subjects were participants in the Coronary Artery Risk Development in Young Adults cohort study, which measured sleep duration and quality using wrist actigraphy, and the Pittsburgh Sleep Quality Index (PSQI).
The initial sleep testing was conducted between 2003 and 2005, when participants were in their 30s and 40s, with follow-up conducted 11 years later.
The assessment consisted of wearing a wrist activity monitor for 3 consecutive days on two separate occasions, roughly 1 year apart, from which the researchers calculated the averages. Participants were asked to report bedtimes and wake times in a sleep diary.
The researchers evaluated midlife cognition using cognitive tests and multivariable logistic regression to examine the association between sleep parameters and poor cognitive performance.
Baseline sleep duration was categorized as short (<6 hours); average (6–7 hours), or long (>7 hours). Participants’ sleep fragmentation was divided into tertiles, and subjective sleep quality was characterized as “good” vs “poor.”
At baseline, the mean sleep duration was 6.1 ± 1.1 hours, and the mean sleep fragmentation index was 19.2 ± 8.1%. Of the participants, close to half (45.6%) reported poor sleep (PSQI global score >5).
The researchers adjusted for an array of variables, including demographics, education, smoking, BMI, depression, physical activity, hypertension, and diabetes.
After adjustment, they found that participants in the highest vs the lowest tertile of the sleep fragmentation index were over twice as likely to have poorer cognitive performance (defined as >1 SD below the mean) on several cognitive tests—particularly those of executive function and fluency, but not verbal memory.
Cognitive tests resulted in the following odds ratios (95% CI):
Digit Symbol Substitution Test (DSST): 2.97 (1.34-6.56)
Fluency: 2.42 (1.17-5.02)
Montreal Cognitive Assessment (MoCA): 2.29 (1.06-4.94)
No association was found between moderate vs lower sleep fragmentation and later cognitive performance. Moreover, the association between sleep fragmentation and cognitive performance didn’t differ by race or sex. Similarly, objective sleep duration and subjective sleep quality were not associated with cognition at midlife.
Strengths and limitations
The researchers point to several study strengths, including the use of both self-reported and actigraphy-measured sleep duration and quality. The diversity of their sample (which included both Black and White adults) was also a strength.
Limitations included the small sample size, making the researchers unable to thoroughly investigate gender or racial differences. They were also unable to control for cognition at baseline. Additionally, they couldn’t assess whether cognition improved with improvement in sleep quality.
They suggest that, based on prior research, sleep deprivation or self-reported poor sleep can contribute to higher cerebrospinal fluid (CSF) amyloid β levels in middle-aged adults and may also be tied to a risk of cardiometabolic diseases. Accumulating evidence suggests that cardiovascular risk factors may accelerate brain aging in midlife.
Bidirectional relationship?
Commenting on the study for MDLinx, Claire Sexton, DPhil, a senior director at the Alzheimer’s Association, noted there is “great interest in the relationship between sleep, cognition, and dementia.”
She cautioned that the study doesn’t “establish causation” and that any relationship between sleep and cognition is likely bidirectional.
"Sleep disruption may be both a risk factor for cognitive decline and a consequence of cognitive decline."
— Claire Sexton, DPhil
Dr. Sexton says the field of Alzheimer’s and dementia research still needs to investigate exactly what components of sleep are important for optimum cognition, and when. She also noted that several studies are underway to better understand if intervening to improve sleep can benefit cognition.[][]
What this means for you
Consider inquiring about patients’ sleep, even for patients in midlife (age 30 to 50). Physicians can also consider early intervention to improve sleep quality in patients with disrupted sleep, as pharmacologic and nonpharmacologic interventions are both viable options for patients whose sleep patterns are less than ideal.