- Taking a nap at 1 p.m. had significant effects on the quality of sleeping during the following night.
- Napping reduced the amount of deep and dream sleep and increased the amount of time spent in light sleep.
- Naps increased concentration of an antibody that protects from respiratory infections.
Sleep is essential to help the body recover from both physical and psychological fatigue suffered throughout the day. Sleep, and one’s level of awakeness during the day, are influenced by the circadian rhythm. One familiar aspect of this daily rhythm is a tendency to feel sleepy and less attentive between 2 and 4 p.m. This postprandial pause often leads to an afternoon nap. Some studies suggest that afternoon naps can interfere with the quality of sleep later that night. In addition, one recent study from China reported that the duration of the afternoon nap was correlated with the rate of coronavirus disease infection in 2019. This discovery raised the question of whether afternoon naps can negatively affect nighttime sleep quality or general health.
In the study by Liang et al., an experiment was conducted to scrutinize the effects of the siesta on the nocturnal sleeping quality and the level of secreted immunoglobulin E (S-IgE) in the saliva, a specific antibody against certain viral or parasitic infections. All subjects reported a regular sleep pattern before testing and were not allowed consumption of alcohol and caffeine-containing foods such as cola, coffee, and chocolate. Strenuous exercises were not allowed for three hours before the testing. Core and skin temperatures were monitored. During the experiment, slow-wave (deep) sleeping duration, light sleeping duration, and rapid eye movement (REM) duration were recorded continuously. A sleeping quality questionnaire survey was conducted 15 minutes after waking to monitor feelings of grogginess, disorientation, drowsiness, and cognitive impairment. Subjects were required to take a 30- to 40-minute nap at 1:00 p.m., under a thermoneutral environment. Subjects of the nonnapping group continued their studying activities in another room.
Napping is both good and bad.
The study found that taking a nap in the afternoon had significant effects on the quality of sleep during the following nocturnal sleep. Napping reduced the amount of time spent in both deep sleep and dream sleep (REM) and increased the amount of time spent in light sleep. Deep sleep is required for the release of many essential hormones necessary for healing and growth. REM sleep is essential for mental health and is critical for memory consolidation during normal sleep cycles. Thus, because subjects who did not take naps had more REM, their next-day cognitive performance and their degree of mental relaxation would be better than the subjects who took naps.
Despite these quantitative changes in nocturnal sleep, the subjects expressed quite positive subjective evaluations of their sleeping quality. The subjects felt as though their nap had no negative effect on the quality of their sleep during the evening.
The subjects who napped had higher S-IgE concentration than the subjects who did not take naps. These results suggest that taking a nap provides a significant benefit for respiratory immunity.
What explains the effect of napping?
Falling asleep at night is usually accompanied by an increase in skin temperature and a decline in core body temperature. This is why good sleep hygiene requires that the bedroom be as cool as possible: It helps the body to transition into a normal sleep cycle. In the current study, the participants who did not take naps had a higher skin temperature and lower core body temperature as compared to the participants who took naps. The authors concluded that taking a daytime nap alters your nighttime thermoregulation and slows the onset of nocturnal sleep as well as disrupts the normal sleep pattern—i.e., less REM and deep sleep. The subjects who took naps had a higher core temperature, which impaired their ability to fall asleep quickly. The higher core temperature may also underlie the higher S-IgE concentration, which is an immunity indicator in healthy people that might convey protection from respiratory tract infections.
In conclusion, the occasional nap is not harmful; just don’t make a habit of napping every day. The reduction in deep sleep and REM dream sleep will ultimately impair daytime cognitive performance.
Liang, S, et al., (2023) Respiratory immunity responses and nocturnal sleeping quality alterations under thermoneutral environments: Does the siesta matter? Indoor and Built Environment.
Mantua J, Spencer RMC. Exploring the nap paradox: are mid-day sleep bouts a friend or foe? Sleep Med 2017; 37: 88–97.
Coiffard B, et al., A Tangled Threesome: Circadian Rhythm, Body Temperature Variations, and the Immune System. Biology 2021; 10: 65.