Naps: The physiology of the ‘Siesta’
Our culture tends to view a nap almost as a sign of weakness of character or laziness. Other cultures incorporate a nap into their daily routine. All ages and species nap. Western society’s view of the nap is yet another reflection of the lack of appreciation of the importance of sleep to alertness.
For good sleep hygiene, naps should be relatively brief (10 to 30 minutes) and completed by early in the afternoon. In general a normal nap is relatively voluntary or elective; it is not overwhelming or irresistible. The latter experience may be an indicator of abnormal daytime sleepiness.
Early in childhood sleep changes from a pattern of frequent, variable length sleep and wake periods to one in which sleep is consolidated at night. There is a clear indication that napping increases again from middle age on, but not necessarily daily. People who nap regularly do not appear to do so because they have a sleep disorder, though people who do are more inclined to fall asleep during the day. Habitual nappers don’t have a different personality than those who don’t nap.
The period from roughly 1PM to 4PM shows the greatest tendency for people to nap. Though there is strong popular view that afternoon sleepiness is related to meals, especially ones rich in carbohydrates, the bulk of evidence shows this not to be true, in general, though it may have some influence in certain individuals. In fact, it is now clear that the tendency to be sleepy and nap then is due to the body’s genetically determined sleep-wake rhythm. There is a biphasic tendency to sleep, afternoon and night. It has been theorized that the midday nap evolved in order to conserve energy and water during the hottest time of the day. The morning and evening, in contrast, are alert periods with little inclination to sleep, the latter sometimes referred to as the “forbidden zone” for sleep.
Napping should be viewed as normal - in fact, encouraged, if it improves alertness, and is especially valuable if sleep the night before was short. There don’t appear to be any negative effects, with two exceptions. The first likely comes from the tendency to go into SWS in the afternoon. Awakening from prolonged naps at that time can be accompanied by a groggy, even confused state termed sleep inertia, usually lasting up to 15 minutes. The other is that prolonged naps, especially over 2 hours long, may reduce nighttime sleep. It is best to keep naps to no longer than 20 to 30 minutes, and recognize that even a 5-minute ‘snooze’ may be beneficial.
