Taking a brief nap on the couch can be a satisfying way to relieve fatigue after a week of overworking. Recent research indicates that even a short nap can work wonders for your memory, mood, and alertness.
According to a study conducted by the National University of Singapore, even shorter naps of 10 minutes can alleviate sleepiness and enhance mood. However, a 30-minute nap is required to improve memory encoding, which is the process of comprehending and retaining new information. The findings were published in the journal Sleep.
The researchers examined 32 young adults who were asked to nap for 10, 30, and 60 minutes on separate days. To compare the prolonged benefits of the different naps, mood, subjective sleepiness, and cognitive performance were assessed at intervals of five, 30, 60, and 240 minutes after awakening.
All nap durations ranging from 10 to 60 minutes provided significant advantages over staying awake. The 10-minute nap was the most suitable choice for avoiding “sleep inertia”, which is the strange drowsy sensation experienced after waking up and not knowing where you are, who you are, or what you’re doing. But this sleep inertia resulted in a temporary decline in the subjects’ performance, which subsided within 30 minutes of waking.
Dr Ruth Leong, a research fellow from the Centre for Sleep and Cognition at the Yong Loo Lin School of Medicine, noted: “Many people are aware of the benefits of napping, but the pressure to use time effectively during the workday can make it difficult for some to nap regularly. We had to inquire if there was a recommended duration for a mid-afternoon nap that would strike a balance between practicality and meaningful benefits. While no definitive “winning” nap duration was identified, a 30-minute nap appears to offer the best combination of practicality and benefit.”
The researchers highlighted the limitations of their findings. The study did not have enough statistical power to examine the impact of habitual napping on nap benefits. Previous studies have shown different benefits of naps depending on nap habits, but this may vary across domains. Future studies may compare habitual and non-habitual nappers to investigate how different nap durations may impact nappers differently. But the study’s sample size may be considered small for the number of questions addressed, and multi-centre studies may be needed to resolve issues of statistical power.
Also, the study only examined a 210-minute delay between encoding and retrieval on the picture encoding task, so it is possible that benefits with the 60-minute nap may have been observed if a longer delay was examined. Future work evaluating the relative efficacy of nap durations on memory encoding could extend delay intervals to investigate this possibility. Similarly, future studies could extend test intervals to assess the temporal trajectory of benefits up to before bedtime, given that benefits of 30-minute and 60-minute naps were observed even up to 240 minutes post-nap.
As the study did not examine nocturnal sleep following the nap, it remains unknown how naps of different durations would impact nocturnal sleep. However, previous experimental work in adolescents has found that naps of 60–90 minutes did not curtail nocturnal sleep, and observational studies have shown that daytime napping in young and middle-aged adults does not impair sleep at night. The relationship between napping and nocturnal sleep may be more mixed in older adults depending on baseline sleep health and total sleep obtained across a 24-hour period, highlighting the need to experimentally evaluate the efficacy of nap durations across different age groups.
All nap durations improved alertness and increased positive mood. But compared to waking, a 30-minute nap incurred minimal sleep inertia and benefited memory encoding. With 10–15 minutes of sleep latency in mind, one should allocate around 40–45 minutes to obtain 30 minutes of sleep for a midday refresh for learning and mood improvement.
