Study details

For the study, researchers from Mass General Brigham and Rush University Medical Center analyzed data from the Rush Memory and Aging Project, which started in 1997 as a cohort study focused on the cognition and neurodegeneration of older, primarily white individuals in northern Illinois.

Starting in 2005, participants in the project wore wrist activity monitors for 10 days to measure their rest activity. The researchers then extracted sleep patterns from the rest-activity data and mapped nap length, frequency, time of day, and day-to-day variability.

The study utilized 19 years' worth of data on 1,338 total participants with an average age of 81 years old. The researchers analyzed the data for associations between napping patterns at the initial assessment and all-cause mortality during the 19-year follow-up period. They found that longer, more frequent, and morning naps were all associated with higher all-cause mortality rates.

Specifically, the researchers found that each additional hour of daytime napping per day was associated with a roughly 13% increased mortality risk, each extra nap per day was associated with around a 7% increased mortality risk, and morning nappers had a 30% higher mortality risk compared to afternoon nappers. Irregular napping was not associated with any increased mortality risk.

However, there were limitations to the study. Since it was an observational study, it only showed a correlation between napping and mortality but not a causal relationship. In addition, the study didn't account for any contributing health conditions, and the sleep trackers only measured movement but not brain activity, meaning rest could be misclassified as sleep in some instances.

In addition, since the study population was limited to older, white adults in the Midwest, it's possible the results may not apply to other groups.

"It is important to note that this is correlation not causation. Excessive napping is likely indicating underlying disease, chronic conditions, sleep disturbances, or circadian dysregulation," Gao said. "Now that we know there is a strong correlation between napping patterns and mortality rates, we can make the case to implement wearable daytime nap assessments to predict health conditions and prevent further decline."