Today is World Sleep Day, where we celebrate the importance of gaining enough sleep and highlight medical conditions as a result of problems in our sleep. However, new studies are showing that while sleep is incredibly important, too much napping may be a cause for concern, particularly in old age.

One recent study, published in Alzheimer's and Dementia, has found a significant correlation between long naps during the day and Alzheimer’s disease, suggesting the behavior may be a precursor to developing the neurological condition, alongside worse cognition later in life. 

Identifying this relationship has been a difficult task, with research often producing conflicting results – some studies have highlighted the positive benefits of napping in later life. Spanish and Latin cultures often partake in siestas, which has been shown in some studies to reduce blood pressure but may also act as a marker for possible health conditions.  

Researchers from the University of California, San Francisco, aimed to delve into napping and extended sleep as a marker for aging and age-related neurological disorders. Taking data from 1,401 participants with an average age of 81, the study looked at the incidence of dementia against daytime napping habits. Each individual wore a wristwatch-like actigraphy device that measures sleep and came in for follow-up appointments up to 14 years later. 

The results found that older adults tended to nap longer and more frequently with age, but that Alzheimer’s dementia doubled the rate at which naps increased as they aged. Long and frequent daytime naps were an indicator of Alzheimer’s dementia and also poorer cognition a year later, and the relationship was bidirectional – those that napped more were more likely to have worse cognition, and those with worse cognition were more likely to nap more the next year. 

On average for people who did not develop cognitive impairment or Alzheimer’s dementia, napping increased by 11 minutes per day. Those diagnosed with mild cognitive impairment increased their napping by 24 minutes, while those diagnosed with Alzheimer’s increased their napping by a staggering 68 minutes, almost triple that of the impairment group. 

“We found the association between excessive daytime napping and dementia remained after adjusting for nighttime quantity and quality of sleep,” said co-senior author Dr Yue Leng of the UCSF Department of Psychiatry and Behavioral Sciences, in a statement. 

“This suggested that the role of daytime napping is important itself and is independent of nighttime sleep.” 

The team believes the study may finally settle the debate over whether napping and dementia are linked, and suggest that the two may share similar mechanisms within the brain. It is also possible that excessive sleep may be indicative of disease, though more research would need to be done. 

The study shows for the first time that napping and Alzheimer’s disease “seem to be driving each other’s changes in a bi-directional way,” said Leng. 

“I don’t think we have enough evidence to draw conclusions about a causal relationship, that it’s the napping itself that caused cognitive aging, but excessive daytime napping might be a signal of accelerated aging or cognitive aging process."