Influence of temperature during your sleep

From Control Systems Technology Group
Revision as of 10:33, 29 February 2016 by S150635 (talk | contribs)
Jump to navigation Jump to search

Back to literature: Literature

Back to main page: PRE2015_3_Groep4

Article: The exact temperature you should sleep at to get a good night’s sleep

Posted by Chris Bailey × January 21, 2014, at 9:33 am

My girlfriend and I share a bed, but our sleeping preferences could not be more different. I like a few, thin sheets, and she likes ten heavy blankets piled on top of one another. She likes a bit of light in the room, and I like it pitch black. She likes the room to be as hot as possible while I like the room to be slightly cool.

Among those variables, the room temperature sticks out the most to me, because it has affected our sleep so much. That motived me to do some research to ask: what’s the exact temperature we should set the thermostat to in order to get a good night’s sleep?

Unfortunately, unlike there is with your office thermostat, there are no definitive answers out there. But over the last couple of weeks I’ve dug deep into the topic, and here are a few suggestions I uncovered for setting your thermostat to get a good night’s sleep:

  • The sleeping temperature recommended by every study I found differed, but most studies recommended setting your thermostat to about 65ºF (18.5ºC). [1]
  • Temperatures below 54ºF and above 75ºF have been shown to be disruptive to your sleep. [2]
  • Before you go to sleep, your body’s internal temperature drops, which “promotes deep continuous sleep”. Setting your thermostat to around 65º will help your body get to that temperature faster, which will let you fall asleep faster, and sleep better. This is why exercising or eating a large meal close to bedtime disrupts your sleep: both activities raise your body’s core temperature. [3]
  • Multiple studies have found that participants with insomnia have a significantly better sleep when they slept in a cooler room.
  • The American Academy of Sleep Medicine suggests “thinking of a bedroom as a cave: It should cool, quiet, and dark.” [4]
  • Everyone’s ideal sleeping temperature is different, and what’s comfortable for you might not be comfortable for someone else. The key is to keep your bedroom at a “thermally neutral” temperature. According to Sleep Number, “thermally neutral means that our body doesn’t have to do anything to create heat (shiver) or shed heat (sweat) to compensate for being too cold or warm.” [5]

For the last couple of months, I’ve been diving deep into experimenting with my sleep. I promise I’ll share more lessons learned as the weeks roll on!

  1. Sources:;;;
  2. Source:
  3. Source:
  4. Source:
  5. Source:

Article: Effects of thermal environment on sleep and circadian rhythm

By Kazue Okamoto-Mizuno and Koh Mizuno

In short The thermal environment is one of the most important factors that can affect human sleep. The stereotypical effects of heat or cold exposure are increased wakefulness and decreased rapid eye movement sleep and slow wave sleep. These effects of the thermal environment on sleep stages are strongly linked to thermoregulation, which affects the mechanism regulating sleep. The effects on sleep stages also differ depending on the use of bedding and/or clothing. In semi-nude subjects, sleep stages are more affected by cold exposure than heat exposure. In real-life situations where bedding and clothing are used, heat exposure increases wakefulness and decreases slow wave sleep and rapid eye movement sleep. Humid heat exposure further increases thermal load during sleep and affects sleep stages and thermoregulation. On the other hand, cold exposure does not affect sleep stages, though the use of beddings and clothing during sleep is critical in supporting thermoregulation and sleep in cold exposure. However, cold exposure affects cardiac autonomic response during sleep without affecting sleep stages and subjective sensations. These results indicate that the impact of cold exposure may be greater than that of heat exposure in real-life situations; thus, further studies are warranted that consider the effect of cold exposure on sleep and other physiological parameters.

Disrupted sleep patterns do not only have effect on daytime activities. Also several other health issues can be affected by a bad nights rest. Things as for example obesity or mortality. Sleep and thermoregulation Many previous studies in humans indicate that sleep is strongly linked to thermoregulation Humans have a sleep-wake rhythm that is repeated in a 24-hour cycle. The core body temperature, which also cycles along with the sleep-wake rhythm, decreases during the nocturnal sleep phase and increases during the wake phase repeatedly in one night. Sleep is most likely to occur when Core temperature decreases, while it hardly occurs during the increasing phases. At the normal sleep onset period in humans, Core temperature decreases due to an underlying circadian rhythm. The driving force behind this Core temperature decrease is the peripheral skin temperature, which is rich in arteriovenous anastomoses and plays a central role in thermoregulation by adjusting blood flow to the skin. The Core temperature decrease in the sleep onset period is also strongly associated with cardiac autonomic activity. It has been suggested that changes in the cardiac autonomic nervous system precede sleep onset, which is strongly associated with changes in body temperature.

The temperature and humidity of the microclimate between humans and bed covers (bed climate) also play crucial roles in creating a warm bed climate temperature to support increased Skin temperature and sleep. The bed climate temperature and relative humidity are generally maintained around 32°C to 34°C, 40% to 60% relative humidity when normal sleep is obtained Besides that bed cover behaviors and body position may have an important role as well. Considering that poor sleepers spend more time on their backs with their heads straight, sleep positions may be related to sleep quality.

Effects of heat exposure Increases in wakefulness are greater in cold Ta (surroundings temperature) than in heat, suggesting that the impact of cold exposure is greater than that of heat exposure. Ta higher or lower than the thermal neutral temperature (29°C) have been shown to increase wakefulness and decrease REM in semi-nude subjects. However, these results are based on semi-nude subjects and exclude the effects of bed covers and clothing. In real-life situations where bed covers and clothing are used, sleep is actually disturbed during heat exposure rather than cold exposure in the young, as well as in the elderly. The increased wakefulness and decreased REM are stereotypical effects that are observed in heat exposure. Wakefulness is the only stage that can cope with an increased thermal load and that wakefulness replaces REM to maintain homoeothermic state. Heat load suppresses the decrease in Core temperature and increases Skin temperature and whole body sweat loss during sleep.

The increased Skin temperature is largely due to increased skin blood flow, which is regulated primarily through two pathways in the sympathetic nervous system: the noradrenergic vasoconstrictor system and the active vasodilator system. Increased Skin temperature during sleep in heat exposure may be largely due to an increased active vasodilator system. There is a possibility that increased vasodilator activity may be related to increased Skin temperature and wakefulness due to heat exposure during sleep.

One of the most important factors that increase heat stress during sleep is the humidity. Humid heat exposure further increases wakefulness and decreases REM, and excessively suppresses the decrease in core temperature, whereas Skin temperature and whole body sweat loss are not affected. Decreased ambient humidity allows sweat to evaporate, thereby dissipating the heat, whereas increased humidity does not allow the sweat to evaporate, causing the skin to remain wet. This is an important fact for understanding what effect the humidity has on the core temperature. Test results indicate that if air conditioning use is limited, then it should be used during the initial segment of sleep. Furthermore, when air conditioning is used in the later segment of sleep, drying off the sweat and changing clothing are essential to avoid chilling effects.

Sleep in older men is more affected by heat exposure than in younger men. This result indicates that the Ta during sleep warrants particularly careful consideration in older men, especially since decreased sleep duration in the older men is related to reduced quality of life and mortality. Ta for the elderly should also take into account clothing conditions. The difference between cold exposure and heat exposure is that cold exposure mainly affects the later segment of sleep, where REM is dominant. In semi-nude sub- jects, cold exposure mainly affects REM due to suppression of the thermoregulatory response. SWS is not affected because it predominates in the initial segment of sleep. In thermoregulation during sleep, Core temperature decreases through the night as the Ta decrease. However, in real-life situations people generally use clothing and bed covers during sleep in cold exposure. In studies using clothing and/or bedding, no significant difference was observed in sleep in a Ta range of 13°C to 23°C and 3°C to 17°C. Also, no significant difference in sleep quality measured by actigraphy was observed between 9°C and 20°C in the elderly. These results indicate that, in real-life situations, cold exposure does not affect sleep.

With regard to cardiac autonomic activity based on the HRV index, the ratio of the low frequency (LF) to high frequency (HF) band (LF/HF) significantly decreases during stage 2 and SWS, while the percentage of the LF component (LF/(LF + HF)) significantly decreases during SWS as the Ta decreases from 17°C to 3°C. In contrast, no significant effect is observed during REM or wakeful- ness. These results may indicate that cardiac parasympathetic activity predominates under cold exposure during stage 2 and SWS, although the results of the LF/HF and LF/(LF + HF) should be interpreted with caution. The dominant parasympathetic activity during stage 2 and SWS may be related to at least three factors: cold stimulation of the head since sufficient thermal insulation of the body is obtained from bedding and clothing; cold air inhalation; and whole body cooling. First, cold stimulation of the face, a unique reflex referred to as cold face test, increases the cardiac parasympathetic activity and the peripheral skin SSNA simultaneously and integrates the trigeminal brain stem reflex arc in wakeful subjects. Additionally, this reflex activates reflex centers located in the medullary region and induces bradycardia. Furthermore, the concomitant increase in the SSNA leads to vasoconstriction, an increase in blood pressure and a significant increase in the HF component. Second, inhalation of cold air may increase muscle sympathetic nervous activity and blood pressure in wakeful subjects. Third, whole body cooling may also be related to increases in systolic and diastolic blood pressure and decreases in heart rate in wakeful subjects. Considering that approximately 70% of sleep time comprises stage 2 and SWS, the cardiac parasympathetic activity may be dominant during sleep in cold exposure. Conclusions Heat exposure affects SWS and REM, whereas cold exposure does not affect sleep stages. Considering that a Ta of 32°C with 80% relative humidity affects only SWS without affecting REM, heat affects SWS first, whereas REM may be well-preserved in real-life situations. Sleep disturbance during heat exposure may lead to behavioral thermoregulation in humans, for example, using an air conditioner to decrease Ta. However, during cold exposure, the cardiac autonomic response may be affected without affecting sleep stages and subjective sensations, and so not trigger behavioral thermoregulation to control Ta. This indicates that the impact of cold exposure may be greater than that of heat; thus, further studies are warranted to consider the effect of cold exposure on sleep and other physiological parameters.




References 1.Gilbert SS, van den Heuvel CJ, Ferguson SA, Dawson D: Thermoregulation as a sleep signalling system. Sleep Med Rev 2004, 8:81–93. 2.Hasler G, Buysse DJ, Klaghofer R, Gamma A, Ajdacic V, Eich D, Rossler W, Angst J: The association between short sleep duration and obesity in young adults: a13-year prospective study. Sleep 2004, 27:661–666. 3.Dew MA, Hoch CC, Buysse DJ, Monk TH, Begley AE, Houck PR, Hall M, Kupfer DJ, Reynolds CF 3rd: Healthy older adults’ sleep predicts all-cause mortality at 4 to 19 years of follow-up. Psychosom Med 2003, 65:63–73. 4.Manabe K, Matsui T, Yamaya M, Sato-Nakagawa T, Okamura N, Arai H, Sasaki H: Sleep patterns and mortality among elderly patients in a geriatric hospital. Gerontology 2000, 46:318–322. 5.Parsons K: Human Thermal Environments. Oxford: Taylor & Francis; 1993. 6.Van Someren EJ: Mechanisms and functions of coupling between sleep and temperature rhythms. Prog Brain Res 2006, 153:309–324. 7.Czeisler C, Buxton O, Khalsa S: The human circadian timing system and sleep-wakeregulation. In Principles and Practice of Sleep Medicine. Edited by Kryger M, Roth T, Dement W. Philadelphia: Elsevier; 2005. 8.Barrett J, Lack L, Morris M: The sleep-evoked decrease of body temperature. Sleep 1993, 16:93–99. 9.Krauchi K, Cajochen C, Werth E, Wirz-Justice A: Functional link between distal vasodilation and sleep-onset latency? Am J Physiol Regul Integr Comp Physiol 2000, 278:R741–R748. 10.Lack L, Gradisar M: Acute finger temperature changes preceding sleep onsets over a 45-h period. J Sleep Res 2002, 11:275–282. 11.Krauchi K, Cajochen C, Wirz-Justice A: Circadian and homeostatic regulation of core body temperature and alertness in humans: what is the role of melatonin? In Circadian Clocks and Entrainment. Edited by Honma K, Honma S. Hokkaido: Hokkaido University Press; 1998. 12.Raymann RJ, Swaab DF, van Someren EJ: Skin temperature andsleep-onset latency: changes with age and insomnia. Physiol Behav 2007, 90:257–266. 13.Van Someren EJ: More than a marker: interaction between the circadian regulation of temperature and sleep, age-related changes, and treatment possibilities. Chronobiol Int 2000, 17:313–354. 14.Okamoto-Mizuno K, Yamashiro Y, Tanaka H, Komada Y, Mizuno K, Tamaki M, Kitado M, Inoue Y, Shirakawa S: Heart rate variability and body temperature during the sleep onset period. Sleep Biol Rhythms 2008, 6:42–49. 15.Krauchi K, Knoblauch V, Wirz-Justice A, Cajochen C: Challenging the sleep homeostat does not influence the thermoregulatory system in men: evidence from a nap vs. sleep-deprivation study. Am J Physiol Regul Integr Comp Physiol 2006, 290:R1052–R1061. 16.Okamoto K, Nagai Y, Iizuka S: Age effects on physiological responses and bed climate during sleep after heating the lower extremities. J Home Economics Japan 1998, 49:1307–1312. 17.Okamoto K, Nagai Y, Iizuka S: Effects of age on physiological response and bed climate during sleep followed by using the electric blanket. J Home Economics Japan 1999, 50:259–265. 18.Monk TH, Reynolds CF 3rd, Buysse DJ, Hoch CC, Jarrett DB, Jennings JR, Kupfer DJ: Circadian characteristics of healthy 80-year-olds and their relationship to objectively recorded sleep. J Gerontol 1991, 46:M171–M175. 19.Okamoto-Mizuno K, Tsuzuki K: Effects of season on sleep and skin temperature in the elderly. Int J Biometeorol 2010, 54:401–409. 20.Raymann RJ, Swaab DF, van Someren EJ: Skin deep: enhanced sleep depth by cutaneous temperature manipulation. Brain 2008, 131:500–513. 21.Van Someren E: Sleep propensity is modulated by circadian and behavior- induced changes in cutaneous temperature. J Thermal Biol 2004, 29:437–444. 22.Okamoto K, Iizuka S, Okudaira N: The effects of air mattress upon sleep and bed climate. Appl Human Sci 1997, 16:97–102. 23.Okamoto K, Mizuno K, Okudaira N: The effects of a newly designed air mattress upon sleep and bed climate. Appl Human Sci 1997, 16:161–166. 24.Yanase T: A study on the physiological and psychological comfort of residential conditions. J Home Economics Jap 1998, 49:975–984. 25.Glotzbach SF, Heller HC: Central nervous regulation of body temperature during sleep. Science 1976, 194:537–539. 26.Parmeggiani PL: Interaction between sleep and thermoregulation: an aspect of the control of behavioral states. Sleep 1987, 10:426–435. 27.Candas V, Libert JP, Muzet A: Heating and cooling stimulations during SWS and REM sleep in man. J Therm Biol 1982, 7:155–158. 28.Jennings JR, Reynolds CF, Bryant DS, Berman SR, Buysse DJ, Dahl RE, Hoch CC, Monk TH: Peripheral thermal responsivity to facial cooling during sleep. Psychophysiology 1993, 30:374–382. 29.Ogawa T, Satoh T, Takagi K: Sweating during night sleep. Jpn J Physiol 1967, 17:135–148. 30.Libert JP, Candas V, Muzet A, Ehrhart J: Thermoregulatory adjustments to thermal transients during slow wave sleep and REM sleep in man. J Physiol Paris 1982, 78:251–257. 31.Sagot JC, Amoros C, Candas V, Libert JP: Sweating responses and body temperatures during nocturnal sleep in humans. Am J Physiol 1987, 252: R462–R470. 32.Dewasmes G, Bothorel B, Candas V, Libert JP: A short-term poikilothermic period occurs just after paradoxical sleep onset in humans: characterization changes in sweating effector activity. J Sleep Res 1997, 6:252–258. 33.Sugenoya J, Iwase S, Mano T, Sugiyama Y, Ogawa T, Nishiyama T, Nishimura N, Kimura T: Vasodilator component in sympathetic nerve activity destined for the skin of the dorsal foot of mildly heated humans. J Physiol 1998, 507(Pt 2):603–610. 34.Amoros C, Sagot JC, Libert JP, Candas V: Sweat gland response to local heating during sleep in man. J Physiol Paris 1986, 81:209–215. 35.Haskell EH, Palca JW, Walker JM, Berger RJ, Heller HC: Metabolism and thermoregulation during stages of sleep in humans exposed to heat and cold. J Appl Physiol 1981, 51:948–954. 36.Palca JW, Walker JM, Berger RJ: Thermoregulation, metabolism, and stages of sleep in cold-exposed men. J Appl Physiol 1986, 61:940–947. 37.Okamoto-Mizuno K, Nagai Y, Iizuka S: The effects of ambient temperature change on the covered area of the body during sleep. J Home Economics Jap 2003, 54:1025–1030. 38.Miyazawa M: On the correlation between bed climate influenced by combinations of mattresses and sleep. Res J Living Science 1976, 23:86–91. 39.De Koninck J, Gagnon P, Lallier S: Sleep positions in the young adult and their relationship with the subjective quality of sleep. Sleep 1983, 6:52–59. 40.Haskell EH, Palca JW, Walker JM, Berger RJ, Heller HC: The effects of high and low ambient temperatures on human sleep stages. Electroencephalogr Clin Neurophysiol 1981, 51:494–501. 41.Okamoto-Mizuno K, Mizuno K: Sleep and environment. Treatment Strageties - Respiratory 2011, 2:87–89. 42.Karacan I, Thornby JI, Anch AM, Williams RL, Perkins HM: Effects of high ambient temperature on sleep in young men. Aviat Space Environ Med 1978, 49:855–860. 43.Okamoto-Mizuno K, Mizuno K, Michie S, Maeda A, Iizuka S: Effects of humid heat exposure on human sleep stages and body temperature. Sleep 1999, 22:767–773. 44.Libert JP, Di Nisi J, Fukuda H, Muzet A, Ehrhart J, Amoros C: Effect of continuous heat exposure on sleep stages in humans. Sleep 1988, 11:195–209. 45.Bach V, Maingourd Y, Libert JP, Oudart H, Muzet A, Lenzi P, Johnson LC: Effect of continuous heat exposure on sleep during partial sleep deprivation. Sleep 1994, 17:1–10. 46.Tsuzuki K, Okamoto-Mizuno K, Mizuno K: Effects of humid heat exposure on sleep, thermoregulation, melatonin, and microclimate. J Therm Biol 2004, 29:31–36. 47.Pierzga JM, Frymoyer A, Kenney WL: Delayed distribution of active vasodilation and altered vascular conductance in aged skin. J Appl Physiol 2003, 94:1045–1053. 48.Sakaguchi S, Glotzbach SF, Heller HC: Influence of hypothalamic and ambient temperatures on sleep in kangaroo rats. Am J Physiol 1979, 237: R80–R88. 49.Okamoto-Mizuno K, Tsuzuki K, Mizuno K: Effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans. Int J Biometeorol 2005, 49:232–237. 50.Okamoto-Mizuno K, Tsuzuki K, Mizuno K, Iwaki T: Effects of partial humid heat exposure during different segments of sleep on human sleep stages and body temperature. Physiol Behav 2005, 83:759–765. 51.Bakkevig MK, Nielsen R: Impact of wet underwear on thermoregulatory responses and thermal comfort in the cold. Ergonomics 1994, 37:1375–1389. 52.Miyazawa M: Air conditioning. In Sleep Environment. Tokyo: Asakura Shoten; 1999:157–163 [Torii S (Series Editor)]. 53.Tsuzuki K, Yokoyama K, Yokoi T, Ogi H, Taya H, Yoshioka M, Nakamura K: Thermal environments and indoor air quality in the elderly houses in a rural area. Jpn J Biometeor 2001, 38:23–32. 54.Sassa N, Isoda N: Study on the consciousness of energy-saving and life style - a case for the detached house of the newly-developed residential area in the suburbs of Nara city. J Home Economics Jap 2003, 54:935–943. 55.Okamoto-Mizuno K, Tsuzuki K, Mizuno K: Effects of mild heat exposure on sleep stages and body temperature in older men. Int J Biometeorol 2004, 49:32–36. 56.Dijk DJ, Duffy JF, Riel E, Shanahan TL, Czeisler CA: Ageing and the circadian and homeostatic regulation of human sleep during forced desynchrony of rest, melatonin and temperature rhythms. J Physiol 1999, 516(Pt 2):611–627. 57.Dijk DJ, Duffy JF, Czeisler CA: Contribution of circadian physiology and sleep homeostasis to age-related changes in human sleep. Chronobiol Int 2000, 17:285–311. 58.Inoue Y, Kuwahara T, Araki T: Maturation- and aging-related changes in heat loss effector function. J Physiol Anthropol Appl Human Sci 2004, 23:289–294. 59.Lushington K, Dawson D, Lack L: Core body temperature is elevated during constant wakefulness in elderly poor sleepers. Sleep 2000, 23:504–510. 60.Dawson D, Rogers NL, van den Heuvel CJ, Kennaway DJ, Lushington K: Effect of sustained nocturnal transbuccal melatonin administration on sleep and temperature in elderly insomniacs. J Biol Rhythms 1998, 13:532–538. 61.Kenney WL, Chiu P: Influence of age on thirst and fluid intake. Med Sci Sports Exerc 2001, 33:1524–1532. 62.Okamoto K, Kudoh Y, Yokoya T, Okudaira N: A survey of bedroom and bed climate of the elderly in a nursing home. Appl Human Sci 1998, 17:115–120. 63.Okamoto-Mizuno K, Tsuzuki K, Ohshiro Y, Mizuno K: Effects of an electric blanket on sleep stages and body temperature in young men. Ergonomics 2005, 48:749–757. 64.Buguet A, Cespuglio R, Radomski MW: Sleep and stress in man: an approach through exercise and exposure to extreme environments. Can J Physiol Pharmacol 1998, 76:553–561. 65.Kreider MB, Iampietro PF: Oxygen consumption and body temperature during sleep in cold environments. J Appl Physiol 1959, 14:765–767. 66.Muzet A, Libert JP, Candas V: Ambient temperature and human sleep. Experientia 1984, 40:425–429. 67.Okamoto-Mizuno K, Tsuzuki K, Mizuno K, Ohshiro Y: Effects of low ambient temperature on heart rate variability during sleep in humans. Eur J Appl Physiol 2009, 105:191–197. 68.Candas V, Libert J, Vogt J, Ehrhart J, Muzet A: Body temperature during sleep under different thermal conditions. In Indoor Climate, Effect on Human Comfort, Performance and health.: Danish Building Research Institute; 1979:763–776. 69.Hilz MJ, Stemper B, Sauer P, Haertl U, Singer W, Axelrod FB: Cold face test demonstrates parasympathetic cardiac dysfunction in familial dysautonomia. Am J Physiol 1999, 276:R1833–R1839. 70.Brown CM, Sanya EO, Hilz MJ: Effect of cold face stimulation on cerebral blood flow in humans. Brain Res Bull 2003, 61:81–86. 71.Gavhed D, Makinen T, Holmer I, Rintamaki H: Face temperature and cardiorespiratory responses to wind in thermoneutral and cool subjects exposed to -10degrees C. Eur J Appl Physiol 2000, 83:449–456. 72.LeBlanc J, Mercier I: Cold wind stimulation reflex. J Appl Physiol 1992, 73:1704–1707. 73.Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation 1996, 93:1043–1065. 74.Heindl S, Struck J, Wellhoner P, Sayk F, Dodt C: Effect of facial cooling and cold air inhalation on sympathetic nerve activity in men. Respir Physiol Neurobiol 2004, 142:69–80. 75.Korhonen I: Blood pressure and heart rate responses in men exposed to arm and leg cold pressor tests and whole-bodycold exposure. Int J Circumpolar Health 2006, 65:178–184. 76.Kloner RA: Natural and unnatural triggers of myocardial infarction. Prog Cardiovasc Dis 2006, 48:285–300. 77.Mercer JB: Cold–an underrated risk factor for health. Environ Res 2003, 92:8–13. 78.Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. The Eurowinter Group. Lancet 1997, 349:1341–1346. 79.Keatinge WR, Coleshaw SR, Cotter F, Mattock M, Murphy M, Chelliah R: Increases in platelet and red cell counts, blood viscosity, and arterial pressure during mild surface cooling: factors in mortality from coronary and cerebral thrombosis in winter. Br Med J (Clin Res Ed) 1984, 289:1405–1408. 80.Rudnicka AR, Rumley A, Lowe GD, Strachan DP: Diurnal, seasonal, and blood- processing patterns in levels of circulating fibrinogen, fibrin D-dimer, C-reactiveprotein, tissue plasminogen activator, and von Willebrand factor in a 45-year-oldpopulation. Circulation 2007, 115:996–1003. 81.Lavery CE, Mittleman MA, Cohen MC, Muller JE, Verrier RL: Nonuniform nighttime distribution of acute cardiac events: a possible effect of sleep states. Circulation 1997, 96:3321–3327. 82.Viola AU, Simon C, Ehrhart J, Geny B, Piquard F, Muzet A, Brandenberger G: Sleep processes exert a predominant influence on the 24-h profile of heart rate variability. J Biol Rhythms 2002, 17:539–547. 83.Ohkubo T, Hozawa A, Yamaguchi J, Kikuya M, Ohmori K, Michimata M, Matsubara M, Hashimoto J, Hoshi H, Araki T, Tsuji I, Satoh H, Hisamichi S, Imai Y: Prognostic significance of the nocturnal decline in blood pressure in individuals with and without high 24-h blood pressure: the Ohasama study. J Hypertens 2002, 20:2183–2189. 84.Verdecchia P, Porcellati C, Schillaci G, Borgioni C, Ciucci A, Battistelli M, Guerrieri M, Gatteschi C, Zampi I, Santucci A, Reboldi G: Ambulatory blood pressure. An independent predictor of prognosis in essential hypertension. Hypertension 1994,24:793–801. 85.Okamoto K, Kimura F, Tsuruhashi R, Iizuka S: A Survey of sleep environment of elderly people. Proceedings of the Jissen Women’s University 1993, 30:63–69. 86.Aschoff J, Tokura H: Circadian activity rhythms in squirrel monkeys: entrainment by temperature cycles. J Biol Rhythms 1986, 1:91–99. 87.Francis AJ, Coleman GJ: The effect of ambient temperature cycles upon circadian running and drinking activity in male and female laboratory rats. Physiol Behav 1988, 43:471–477. 88.Refinetti R: Entrainment of circadian rhythm by ambient temperature cycles in mice. J Biol Rhythms 2010, 25:247–256. 89.Dewasmes G, Nicolas A, Rodriguez D, Salame P, Eschenlauer R, Joly D, Muzet A: Human core temperature minimum can be modified by ambient thermal transients. Neurosci Lett 1994, 173:151–154. 90.Togo F, Aizawa S, Arai J, Yoshikawa S, Ishiwata T, Shephard RJ, Aoyagi Y: Influence on human sleep patterns of lowering and delaying the minimum core body temperature by slow changes in the thermal environment. Sleep 2007, 30:797–802. 91.Teramoto Y, Oikura H, Ioki I, Suho S, Inoshiri R, Masuda M: The effect of room temperature on rectal temperature during night sleep. J Therm Biol 1998, 23:15–21. 92.Wakamura T, Tokura H: Circadian rhythm of rectal temperature in humans under different ambient temperature cycles. J Therm Biol 2002, 27:439–447. 93.Dewasmes G, Signoret P, Nicolas A, Ehrhart J, Muzet A: Advances of human core temperature minimum and maximal paradoxical sleep propensity by ambient thermal transients. Neurosci Lett 1996, 215:25–28. 94.Muzet A, Ehrhart J, Candas V, Libert J, Vogt J: REM sleep and ambient temperature in man. Int J Neuroscience 1983, 18:117–125. 95.Czeisler CA, Zimmerman JC, Ronda JM, Moore-Ede MC, Weitzman ED: Timing of REM sleep is coupled to the circadian rhythm of body temperature in man. Sleep 1980, 2:329–346. 96.Okamoto K, Nakabayashi K, Mizuno K, Okudaira N: Effects of truss mattress upon sleep and bed climate. Appl Human Sci 1998, 17:233–237. 97.Okada M, Midorikawa-Tsurutani T, Tokura H: The effects of two different kinds of quilt on human core temperature during night sleep. Ergonomics 1994, 37:851–857. 98.Park SJ, Tokura H: Effects of different types of clothing on circadian rhythms of core temperature and urinary catecholamines. Jpn J Physiol 1998, 48:149–156. 99.Krauchi K, Wirz-Justice A: Circadian rhythm of heat production, heart rate, and skin and core temperature under unmasking conditions in men. Am J Physiol 1994, 267:R819–R829. 100.Kondo M, Tokura H, Wakamura T, Hyun KJ, Tamotsu S, Morita T, Oishi T: Physiological significance of cyclic changes in room temperature around dusk and dawn for circadian rhythms of core and skin temperature, urinary 6-hydroxymelatonin sulfate, and waking sensation just after rising. J Physiol Anthropol 2007, 26:429–436. 101.Shido O, Sugimoto N, Tanabe M, Sakurada S: Core temperature and sweating onset in humans acclimated to heat given at a fixed daily time. Am J Physiol 1999, 276:R1095–R1101. 102.Klerman EB, Rimmer DW, Dijk DJ, Kronauer RE, Rizzo JF 3rd, Czeisler CA: Nonphotic entrainment of the human circadian pacemaker. Am J Physiol 1998, 274:R991–R996. 103.Kondo M, Tokura H, Wakamura T, Hyun KJ, Tamotsu S, Morita T, Oishi T: Combined influences of gradual changes in room temperature and light around dusk and dawn on circadian rhythms of core temperature, urinary 6-hydroxymelatonin sulfate and waking sensation just after rising. Coll Antropol 2007, 31:587–593. 104.Van Someren E: Thermosensitivity of the circadian timing system. Sleep and Biological Rhythms 2003, 1:55–64.