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Many times we can read on the newspaper or on social media, or hear on the radio or on television, that is important to follow a proper sleeping schedule and take care of one’s quality of sleep. It is indeed very true that sleeping properly is linked to a healthier body weight, increased concentration and productivity, decreased risk for heart diseases and diabetes, and an overall better health. Noticeably, sleep quality has been researched extensively in its links to dementia.

Often times we are advised to sleep at least 8 hours per day, but is there any fundament to this well-known notion, particularly with regards to dementia? Perhaps not exactly 8, but close enough.

In 2015 a large group of scientists concluded a very large study, exploring sleep duration of over 7400 women, and its link to dementia and cognitive decline. What they found out was rather surprising. Not only they confirmed that sleeping 6 or less hours per night, for a prolonged period of time, is correlated with a higher degree of cognitive decline and higher rates of dementia, which was something they were expecting, but also, and more surprisingly, that sleeping 8 or more hours per night was associated with the same risks.

The risk was estimated to be very similar. The scientists found out that the risk for short sleepers was increased by 36%, while the risk for long sleepers was increased by 35%. Scientists were not able however to explain why exactly did long sleepers experience an increased risk. They hypothesized a longer sleep being an indicator of a proinflammatory state which may play a role in the subsequent developing of dementia, or a reset of the circadian rhythm (our internal clock or sleep/wake cycle), which may play a role in developing neurodegenerative diseases.

Regardless, what they found out is that consistent bad sleeping habits, specifically either under-sleeping or over-sleeping, play an influential role in whether a person goes on developing cognitive decline and dementia.


source: Chen et al. (2015), Sleep duration, cognitive decline, and dementia risk in older women, Alzheimer and Dementia, 12(1), pp. 21-33.