A seemingly harmless daytime nap may carry unexpected significance for brain health in later life. New research linked frequent daytime napping, especially sleep that happens unintentionally, with a higher risk of developing dementia among older adults.

The study, published in The Journal of Gerontology: Medical Sciences, came from researchers at the Johns Hopkins Bloomberg School of Public Health. The team tracked nearly 1,000 adults who were age 65 or older.

None of the participants showed signs of memory or thinking problems when the study began in 2013. A decade later, researchers examined how their daytime rest habits related to long term brain health.

Those habits included how frequently participants napped, how long they slept during the day and whether they fell asleep accidentally. The findings indicated that these details may provide information that nighttime sleep duration or quality alone cannot capture.

Participants who napped most days or every day had a 48% higher risk of developing dementia compared with people who rarely or never napped. Whether that daytime sleep was planned also appeared to matter.

Older adults who fell asleep unintentionally during the day had a 39% higher risk of dementia. Short naps were also linked to poorer outcomes in the study.

Naps lasting 30 minutes or less were associated with a 40% higher risk of dementia, even after researchers adjusted for other health factors. For naps lasting longer than 30 minutes, the association became less pronounced after nighttime sleep patterns were considered.

Study authors Adam Spira, Ph.D., a professor at the Bloomberg School, and postdoctoral fellow Kening Jiang, Ph.D., emphasized that duration is only one part of the picture.

“Our study highlights the importance of looking beyond just how long people nap and considering other napping characteristics, such as how frequently they nap and whether their naps are intentional,” Spira and Jiang told Fox News Digital.

They added, “This study provides important longitudinal evidence that frequent and unintentional daytime napping were associated with a higher risk of developing dementia among older adults.”

The findings remained consistent after the researchers accounted for nighttime sleep length, daytime drowsiness and indicators of sleep apnea. The team also stressed that nighttime sleep and daytime napping are closely connected.

“Nighttime sleep and daytime napping are closely related,” Spira and Jiang said. “Daytime napping may compensate for poor nighttime sleep, but it may also reduce the drive to sleep at night, potentially contributing to nighttime sleep disturbances, another important potential risk factor for dementia.”

Despite the associations, the researchers did not conclude that daytime naps directly cause changes in the brain. Instead, changing nap habits could represent an early warning sign of underlying brain changes.

Brain regions involved in regulating wakefulness can begin to deteriorate during the early stages of dementia, according to the researchers. Those changes can lead to more frequent fatigue during the day.

To examine whether early dementia cases were driving the results, the team analyzed the data again after excluding anyone who developed dementia during the first five years. The association involving frequent and accidental naps remained just as strong.

That finding suggested that changes in daytime napping patterns can emerge years before a formal dementia diagnosis. Still, the research team emphasized that the study was observational and had limitations.

“We did not directly intervene on participants’ napping behaviors to examine whether changing these behaviors would affect their dementia risk,” Spira and Jiang told Fox News Digital.

“Although we don’t know whether napping causes dementia, our study findings suggest that daytime napping patterns may be useful indicators of future dementia risk,” they added. The findings indicate that frequent or unintentional daytime naps among older adults may be worth monitoring.