A study published on February 23 found that a half-hour nap in the afternoon is associated with a mid-day “refresh.”
“Many know the benefits of napping, but the pressure to optimize time in the workday poses constraints for some on the practicality of napping regularly,” said study coauthor Dr Ruth Leong from the Centre for Sleep and Cognition at the Yong Loo Lin School of Medicine, National University of Singapore, when outlining the motivation for the study.
Naps are defined as short periods of sleep that occur outside a main nocturnal period, and that are different from bouts of uncontrollable and unintended sleep. While the latter may underlie significantly inadequate nocturnal sleep, jetlag, a sleep disorder, or a neurological condition,
voluntary naps often serve as an intended midday refresh that can enhance learning and productivity.
Is there a recommended duration for a mid-afternoon nap that achieves a balance between practicability and meaningful benefits? This question was addressed in the study.
Following their usual amount of night-time sleep, 32 young adults underwent four experimental conditions: awake, a 10-minutes nap, a 30-minute nap, and a 60-minute nap on separate days.
The researchers compared sleep time measured objectively with polysomnography rather than just the amount of time provisioned for the nap. This allowed for unambiguous decision-making about how long one should allocate for a nap, taking into account the average time taken to fall asleep. Mood, subjective sleepiness, cognitive performance were measured at intervals of five minutes, 30 minutes, 60 minutes and 240 minutes after waking from the mid-afternoon naps to compare how long the respective nap benefits lasted. The effect of these nap lengths on memory encoding was also examined.
On average, participants took 10 to 15 minutes to fall asleep. Compared to wake, all nap durations ranging from 10 to 60 minutes had clear benefits for positive mood, subjective sleepiness, and alertness that lasted up to 240 minutes post-nap, suggesting that even a short 10-minutes can act as a midday refresh.
However, only the 30-minute nap had benefits for memory encoding, indicating that minimally, 30 minutes may be needed for benefits to memory.
Improvements for vigilance were moderate, and benefits for speed of processing were not seen. Sleep inertia — the grogginess just after waking that can manifest as temporary decrements in performance — was observed only for the 30 to 60 minutes naps. Even so, decrements were minimal and were resolved within 30 minutes of waking.
While no clear “winning” nap duration was found, a 30-minute nap appeared to have the best trade-off between practicability and benefit.
To read the full study, published in Sleep, click here