An afternoon snooze might seem appealing to middle-aged folks and seniors, but these naps could carry a high cost.

People with certain types of napping patterns have a greater risk of an early death, researchers are slated to report at an upcoming meeting of the American Academy of Sleep Medicine (AASM).

“People who slept longer during the day, had irregular daytime sleep patterns, or slept more around midday and early afternoon were at greater risk, even after accounting for health and lifestyle factors,” lead researcher Chenlu Gao, a postdoctoral research fellow at Massachusetts General Hospital in Boston, said in a news release.

The findings call into question the whole concept of the "power nap."

For the study, researchers analyzed data on more than 86,500 people participating in the UK Biobank long-term health research project. 

These folks had their sleep habits monitored for a week using wrist devices, and researchers compared those habits to death records. Their average age was 63 at the time their napping was tracked.

Nearly 5,200 people died during a follow-up of 11 years, researchers said.

Results showed an increased risk of premature death for:

• People who tended to take longer daytime naps.

• Folks whose napping patterns fluctuated frequently.

• People who napped between 11 a.m. and 3 p.m.

This last observation contradicts AASM guidelines, which encourages adults to limit themselves to “power naps” of no more than 20 to 30 minutes in the early afternoon, researchers noted.

Naps that last longer than a half-hour can cause grogginess that undercuts the potential helpfulness of a siesta, researchers said.

“Interestingly, the data that shows risks associated with napping around midday and early afternoon contradicts what we currently know about napping, so further research on that link could be warranted,” Gao said.

Gao is to present these findings Wednesday during the AASM's annual meeting in Seattle.

Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.