In a new longitudinal study, investigators discovered that older adults who sleep less than 4.5 hours or more than 6.5 hours a night report significant cognitive decline over time, but the cognitive scores for those with sleep duration in between the range, remain stable.

The study was published online on the 20th of October this year in the journal Brain, as part of a growing body of research that looks to address if sleep can be used as a marker of Alzheimer’s disease progression. Previous studies have suggested a strong relationship between sleep patterns and Alzheimer’s disease, which affects close to 6 million Americans.

So if the research is really on to something, to protect your brain you need to get a minimum of four and a half hours sleep a night and no more than six and a half, so set your alarm clock for a 6 am wake up call if you’re hitting the hay at midnight and you’ll be within safe limits.

The studies lead author Brendan Lucey, MD, MSCI, associate professor of neurology and director of the Washington University Sleep Medicine Center, St. Louis, Missouri had this to say;

“This really suggests that there’s this middle range, a ‘sweet spot,’ where your sleep is really optimal,”

Sleep, AD and Cognitive function

The problem researchers face is unwinding the complex relationship shared by sleep, Alzheimer’s Disease (AD), and cognitive decline. In an earlier study by the same group, poor sleep quality was associated with early signs of AD, and a report published in September found that elderly people who slept less than 6 hours a night had a greater burden of amyloid-beta, a hallmark sign of AD.

For this particular study, however, researchers monitored sleep-wake activity over 4–6 nights in 100 participants who underwent annual cognitive assessments and clinical studies, including APOE genotyping, as part of a longitudinal study at the Knight Alzheimer Disease Research Center at Washington University.

Participants also provided cerebrospinal fluid (CSF) total tau and amyloid-β42 and wore a small EEG device on their forehead while they slept. The majority of participants had a clinical dementia rating (CDR) score of 0, indicating no cognitive impairment. Twelve individuals had a CDR >0, with most reporting mild cognitive impairment. For more details on the trial itself, please refer to the linked article above.

What does the new data mean?

Understanding how sleep changes at different stages of AD could help researchers determine if sleep can be used as a marker of disease progression, which could in turn lead to interventions to slow that process. It’s like identifying a tell tales symptom that allows AD patients to be identified for possible treatment.

The upshot is that you want to try and ensure at least six hours of restful sleep a night, which, as you age, can prove challenging. As I age I now often find myself wide awake at 4 am and inevitably resort to coffee and the laptop, two terrible habits that are guaranteed to ban any further thought of sleep.

These are patterns we need to be aware of and try to address to ensure we’re hitting that sweet spot. Our sleep patterns may however reveal far more and as this research highlights, could soon be used as markers for certain conditions.

According to Lucey, who plans to repeat the study,

“We’re not at the point yet where we can say that we need to monitor someone’s sleep time and then do an intervention to see if it would improve their risk for cognitive decline, but that’s a question I’m very excited to try to answer.”

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