Short sleep duration or sleeping less than seven hours each night linked to a higher risk of dementia onset among individuals aged 57-69, defined as younger-older adults. While, this linked to a lower risk of developing the condition among older-older adults aged 70 or older. Detecting this sleep pattern may help physicians or families identify individuals at risk of dementia earlier. It may also help those at risk proactively take action to delay dementia onset.  

Our sleep duration changes as we age. For instance, the duration of the rapid eye movement sleep, the stage where most dreams occur, starts to decline at around age of 60. Another example is that after individuals turned 40 years old, the percentage of time spent asleep while in bed, also called sleep efficiency, decreases every decade. Previous studies have explored the links between sleep duration, sleep disturbances, and the risk of developing dementia. While, there is no definite conclusion yet on the link between short sleep period and dementia. 

To further look at this link, since 2008, researchers from Sweden and the UK started following up 7223 participants without dementia living in England. During the next 10 to 11 years, the researchers asked the participants to self-report the average hours of sleep each night from Monday to Friday. Then the researchers categoried less than seven hours as short sleep, seven to eight hours as ideal sleep, and over eight hours as long sleep. To determine whether the participants developed dementia over the years, they used two approaches. One is the diagnosis of dementia by a physician, another one is the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) results shared by families or caregivers. Until 2019, 409 of the participants developed the condition.  

Among the older-older adults aged 70 years or over, the risk of developing dementia among those with short sleep was lower by 26% than individuals who had ideal sleep period. While, for those aged between 57 and 69, or younger-older adults who slept less than seven hours, the risk was higher by 81%. 

The risk of dementia was higher by 71% among older-older adults who had long sleep, however, long sleep did not have negative impact on younger-older adults. This finding also echoes the different effects of short sleep on older- and younger-older adults. 

Another study published this year also showed that in Greece, older-older adults with dementia slept noticeably longer each night, compared to those without the condition who slept about seven hours. 

Younger-older adults who sleep less than seven hours each night have higher risk of developing dementia. The researchers also suggest that long sleep may be an early sign of changes in cognitive ability or dementia among older-older adults. By paying attention to this, physicians, families, or the older adults themselves could proactively prevent progression of the conditions. 

This study was published in Psychiatry Research. Image credit: Canva

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