Traditional sleep advice has focused on the number of hours a person sleeps. But for older adults, the quality of sleep may affect cognitive performance the following day regardless of their quantity of sleep, a new study shows. Sleep quality was based on how much time someone was awake between when they first went to sleep and when they rose in the morning.

For the study, researchers analyzed data from 261 participants over age 70 who lived in the community in Bronx County, New York.

For 16 days, participants wore smart watches that tracked their sleep. They also completed cognitive assessment “games” six times a day on a smartphone — when they woke up, before they went to bed and four randomly selected times throughout the day. The games took roughly four minutes each, and measured different aspects of cognitive performance including visual working memory, visuospatial memory and processing speed. At the study’s conclusion, the researchers had collected a total of 20,532 cognitive assessments from the participants.

On average, participants slept 7.2 hours each night and spent just over one hour awake during a given night of sleep. Additionally, participants took an average of 0.4 naps each day, which is two naps every five days.

Analyses showed that when an individual was awake for 30 minutes longer during the night than their average amount, their processing speed was slower than usual the next day. Napping the previous day, bedtime and quantity of sleep showed no effect on processing speed or any other aspects of cognitive performance.

Overall, older adults who, on average, spent more time awake during their night’s sleep performed worse on three of the four cognitive tests. In addition to slower processing speed, they performed worse on two tests of visual working memory.

For older adults with sleep problems, researchers recommended evaluating their sleep environment — including avoiding screens before bed and sleeping in dark, quiet conditions at a consistent time. If problems persist, cognitive behavior therapy is an effective option.

To read the full study, published in Sleep Health, click here