Naps can be amazing. They can rejuvenate you in a variety of ways, such as boosting alertness, reaction time, memory, and problem-solving.
Short naps might offset some of the damage wrought by sleep deprivation and could even help reduce the risk of dementia.
But a new study suggests that in older adults, certain nap patterns could be a warning sign worth paying attention to.
Taking a lot of daytime naps, especially in the morning, is associated with higher mortality rates for older adults, researchers in the US found.
This "excessive" napping may signal underlying or developing health problems, they note, and could represent a trackable metric for early detection.
"Our study is one of the first to show an association between objectively measured nap patterns and mortality, and suggests there is immense clinical value in tracking napping patterns to catch health conditions early," says first author Chenlu Gao, a sleep scientist at Mass General Brigham.
Previous research has also linked frequent napping with specific health problems, including hypertension and stroke, but the overall relationship remains poorly understood.
There is evidence of correlation, for example, but little clarity about causation. Naps don't necessarily promote the ailments with which they're associated, and may be beneficial – if inadequate – attempts to mitigate some pre-existing health problem.
And despite strong evidence for a link between naps and illness, there are still key questions about the mere association, let alone what's causing what. This is partly due to limitations in the existing data.
"Excessive napping later in life has been linked to neurodegeneration, cardiovascular diseases, and even greater morbidity, but many of those findings rely on self-reported napping habits and leave out metrics like when and how regular those naps are," Gao says.
Between 20 and 60 percent of older adults take daytime naps, and many are likely invigorating, or at least innocuous. While excessive napping is linked to a range of maladies, further study of these links has been hindered by data that lack objectivity and granularity.
In hopes of addressing this, Gao and her colleagues used information from the Rush University Memory and Aging Project, which began in 1997 as a cohort study of cognitive abilities and neurodegeneration in hundreds of over-55s from northern Illinois.
The study incorporated wrist monitors in 2005 to record people's behavior over an average period of 10 days and differentiate between periods of activity and rest.
Those activity monitors remained a feature of the ongoing study, contributing to two decades of available statistics from a total of 1,338 individuals by 2025.
Equipped with all this objective data on napping patterns, the authors of the new study could apply rigorous scrutiny to factors such as nap length, frequency, and time of day, as well as variability in people's daily napping habits.
Looking at napping patterns at the outset and all-cause mortality over 19 years of follow-up, the researchers found that longer and more frequent naps, as well as morning naps, were associated with a higher risk of death.
Each extra hour of daily napping was associated with a roughly 13 percent higher mortality risk, the study found. Each additional nap per day was also linked with a 7 percent higher risk of dying during the follow-up period.
The time of day seems to matter, too. The mortality risk for morning nappers is about 30 percent higher than that of early afternoon nappers, the study suggests.
Again, this does not necessarily mean napping is responsible.
"It is important to note that this is correlation, not causation," Gao says. "Excessive napping is likely indicating underlying disease, chronic conditions, sleep disturbances, or circadian dysregulation."
Rather than discouraging daytime dozing, these findings cast naps as potentially valuable clues about a person's health.
Related: Scientists Reveal The Optimal Amount of Sleep to Lower Dementia Risk
"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," Gao says.
The study was published in JAMA Network Open.