A siesta (Spanish pronunciation: [ˈsjesta]) is a short nap taken in the early afternoon, often after the midday meal. Such a period of sleep is a common tradition in some countries, particularly those where the weather is warm.
Since the siesta is the traditional daytime sleep of Spain, and through Spanish influence, of many Hispanic American countries and in the Philippines, the word siesta has been taken from Spanish, from the Latin hora sexta – "the sixth hour" (counting from dawn, therefore noon, hence "midday rest"). Einhard's Life of Charlemagne recounts the emperor's summertime siesta: "In summer, after his midday meal, he would eat some fruit and take another drink; then he would remove his shoes and undress completely, just as he did at night, and rest for two or three hours."[1]
Factors explaining the geographical distribution of the modern siesta are mainly high temperatures and heavy intake of food at the midday main meal. Combined, these two factors contribute to the feeling of post-lunch drowsiness. In these countries, the heat can be unbearable in the early afternoon, making a midday break at home ideal. However, in the cold Patagonia, people have siestas too. This could indicate that siestas have a stronger relation with culture than with climate.
The original concept of a siesta seems to have been merely that of a midday break intended to allow people to spend time with their friends and family.
A siesta takes place when the sun is at its highest point. This is when the sun's ultraviolet radiation is at its peak at midday. Prolonged exposure to ultraviolet radiation may result in sunburn, especially if one has fair skin. Recurring overexposure to ultraviolet radiation can cause some forms of skin cancer.
The sun's infrared radiation causes high air temperatures from the midday onwards, the highest temperatures taking place in the early afternoon. High temperatures can cause fatigue or in more serious cases heat exhaustion, hyperthermia (sunstroke) and death.
Older, pre-teenage children are usually capable of napping, but acquire the ability to nap as teenagers as well.[2]
The timing of sleep in humans depends upon a balance between homeostatic sleep propensity, the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode, and circadian rhythms which determine the ideal timing of a correctly structured and restorative sleep episode. The homeostatic pressure to sleep starts growing upon awakening. The circadian signal for wakefulness starts building in the (late) afternoon. As Harvard professor of sleep medicine Charles A. Czeisler notes, "The circadian system is set up in a beautiful way to override the homeostatic drive for sleep."[3]
Thus, in many people, there is a dip when the drive for sleep has been building for hours and the drive for wakefulness has not yet started. This is, again quoting Czeisler, "a great time for a nap."[3] The drive for wakefulness intensifies through the evening, making it difficult to get to sleep 2–3 hours before one's usual bedtime when the wake maintenance zone ends.
In some individuals, "postprandial dip", a brief drop in blood glucose levels caused by the body's normal insulin response to a heavy meal, may produce drowsiness after the meal that can encourage a nap. However, the appearance of the dip is primarily circadian as it occurs also in the absence of the meal.
The concept of a midday nap is also prominent in other tropical or subtropical countries, where the afternoon heat dramatically reduces work productivity. The Washington Post of February 13, 2007 reports at length on studies in Greece that indicate that those who nap have less risk of heart attack.[4]
In the United States, the United Kingdom, and a growing number of other countries, a short sleep has been referred to as a "power nap", a term coined by Cornell University social psychologist James Maas[5] and recognized by other research scientists such as Sara Mednick[6] as well as in the popular press.[7]
Although many cultures acknowledge the benefits of a siesta, or midday nap, this custom is in decline.[citation needed] Because many people now commute between home and work in much greater distances than in the past, it makes it harder to find a common time and place to rest each day. In Spain specifically, while under the threat of an economic crisis, an increasing number of people swap a lunchtime rest for extra hours of work.[citation needed]
The siesta habit has recently been associated with a 37% reduction in coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep (Naska et al., 2007).
Nevertheless, epidemiological studies on the relations between cardiovascular health and siesta have led to conflicting conclusions, possibly because of poor control of moderator variables, such as physical activity. It is possible that people who take a siesta have different physical activity habits, e.g. waking earlier and scheduling more activity during the morning. Such differences in physical activity may mediate different 24-hour profiles in cardiovascular function. Even if such effects of physical activity can be discounted for explaining the relationship between siesta and cardiovascular health, it is still unknown whether it is the daytime nap itself, a supine posture or the expectancy of a nap that is the most important factor.
It was recently suggested that a short nap can reduce stress and blood pressure (BP), with the main changes in BP occurring between the time of lights off and the onset of stage 1 (Zaregarizi, M. 2007 & 2012). Dr. Zaregarizi and his team have conducted that the acute time of falling asleep was where beneficial cardiovascular changes take place. This study has indicated that a large decline in blood pressure occurs during the daytime sleep-onset period only when sleep is expected however when subjects rest in a supine position, the same reduction in blood pressure is not observed. This blood pressure reduction may be associated with the lower coronary mortality rates seen in Mediterranean and Latin American populations where siestas are common.
Dr. Zaregarizi assessed cardiovascular function (blood pressure, heart rate, and measurements of blood vessel dilation) while nine healthy volunteers, 34 years of age on average, spent an hour standing quietly; reclining at rest but not sleeping; or reclining to nap. All participants were restricted to 4 hours of sleep on the night prior to each of the sleep laboratory tests. During the three phases of daytime sleep, he noted significant reductions in blood pressure and heart rate. By contrast, they did not observe changes in cardiovascular function while the participants were standing or reclining at rest.
These findings also show that the greatest decline in blood pressure occurs between lights-off and onset of daytime sleep itself. During this sleep period, which lasted 9.7 minutes on average, blood pressure decreased, while blood vessel dilation increased by more than 9 percent. “There is little change in blood pressure once a subject is actually asleep," Dr. Zaregarizi noted, and he found minor changes in blood vessel dilation during sleep (Zaregarizi, M. 2007 & 2012).
Naska, A., Oikonomou, E., Trichopoulou, A., Psaltopoulou, T. and Trichopoulos, D. (2007). Siesta in healthy adults and coronary mortality in the general population. Archives of Internal Medicine, 167, 296-301.
MohammadReza Zaregarizi, Ben Edwards, Keith George, Yvonne Harrison, Helen Jones and Greg Atkinson. (2007). Acute changes in cardiovascular function during the onset period of daytime sleep: Comparison to lying awake and standing. American J Appl Physiol 103:1332-1338.
MohammadReza Zaregarizi (Author). Effects of Exercise & Daytime Sleep on Human Haemodynamics: With Focus on Changes in Cardiovascular Function during Daytime Sleep Onset. BOOK, ISBN (978-3-8484-1726-1), March, 2012.
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