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25-Year Follow-Up Study Reveals Link Between Sleep in Midlife and Dementia Diagnoses

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Olivia Murillo

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Across our lives, the quantity and quality of sleep that we get will change dramatically, and unfortunately, sleeping less and sleeping worse are common complaints among aging populations. Research examining sleep in older adults is uncovering important connections between sleep and age-related health outcomes, including diseases such as dementia.

A recent study found that getting six or fewer hours of sleep at age 50 and 60, compared with the recommended seven hours, was associated with an increased risk for dementia, even after accounting for sociodemographic, physical, and mental health factors.

The study aimed to determine whether the amount of sleep people get mid-life was related to whether or not they would develop dementia in the future. Researchers collected and analyzed data from 7,959 participants aged 45-55 between 1985-1988, then tracked dementia diagnoses over an average of 25 years.

Researchers also collected information on these participants’ mental, cardiometabolic, and general health to factor into analyses.

At the time of follow-up, there were a total of 521 dementia diagnoses among the participants, now 70 to 75 years old.

Those who had reported getting seven hours of sleep over two decades prior now had the lowest rate of diagnoses, while respondents who had reported getting six or fewer hours of sleep were found to have a significantly higher risk for dementia (Table 1).

Analyses revealed a similar set of results in a group of 55-65 year-olds after an average 15 year follow-up. In a final group of 65-75 year-olds, however, the relationship between sleep and dementia was not as significant once other health-related and behavioral factors were taken into account.

Some participants were asked about their sleep duration on one more occasion between their original measurement and follow-up. The researchers found that people who had reported sleeping six or fewer hours in both their 50s and 60s had a much greater risk for dementia diagnoses compared to those with any other pattern of responses across measurements.

Of note, this study did not find a significant relationship between sleeping eight or more hours and dementia diagnoses.

As sleep and mood disorders are known to be intimately related, a key contribution of this study was its statistical consideration of mental health factors when examining the sleep-dementia relationship.

This provided evidence that these factors are not secretly driving the association. While mood disorders, such as depression, are still believed to play a pivotal role, the findings suggest there exists a consistent, independent relationship between sleep duration in midlife and dementia.

Further studies are required to investigate why short sleep duration, and sleep disturbances at large, can have a negative effect on healthy aging and sleep, which will help identify preventative routes that can be taken earlier in life.

Table 1. Association between sleep duration at age 50 and incidence of dementia

Sleep duration at age 50 N cases / N total Model 1

Hazard Ratio**, accounting for sociodemographic factors

Model 1 + behavioral factors Model 1 + health-related factors
Short (≤ 6 hours) 211/3149 1.28* 1.27* 1.22*
Normal (7 hours) 219/3624 1 (ref) 1 (ref) 1 (ref)
Long (≥ 8 hours) 91/1186 1.25 1.25 1.24

* statistically significant** The hazard ratio is the comparison between the probability of dementia in the short and long sleep groups compared to the normal sleep group.

Table 2. Association between sleep duration at age 60 and incidence of dementia

Sleep duration at age 60 N cases / N total Model 1

Hazard Ratio, adjusted for sociodemographic factors

Model 1 + behavioral factors Model 1 + health-related factors
Short (≤ 6 hours) 192/2759 1.48* 1.46* 1.38*
Normal (7 hours) 142/2988 1 (ref) 1 (ref) 1 (ref)
Long (≥ 8 hours) 75/1417 1.15 1.17 1.13

* statistically significant

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About Our Editorial Team

author
Olivia Murillo

Contributing Writer

About Our Editorial Team

author
Olivia Murillo

Contributing Writer

  • References

    +1 Sources
    1. 1. Sabia, Fayosse, A., Dumurgier, J., et al. (2021). Association of sleep duration in middle and old age with incidence of dementia. Nature Communications, 12, 2289. Published.https://pubmed.ncbi.nlm.nih.gov/33879784/

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