URC

Assessing the Relationship between Sex, Temperature and Sleep

John Wayland
University of Wales, Newport


Abstract

Circadian rhythms exert various physiological influences that encourage sleep. However, the relationship between temperature, sex, and sleep is complex. This study examined the relationship between these factors using an online questionnaire. Participants consisted of 83 females and 47 males who rated their temperature and length of sleep. Results indicated differences between and within sexes but found that neither temperature nor the interaction between these factors influenced the length of sleep that participants recorded. Explanations suggest that the subjective nature of the experiment may have influenced the result. Consideration is therefore given to future integration of subjective responses alongside readings of temperature. Additionally, a longitudinal study is suggested to assess temperature change over a substantial period of development.

Keywords: circadian rhythms, body temperature, sleep patterns, sex

Sleep is a vital part of any individual’s day. On average, individuals will sleep for a total of 175,000 hours in their lifetime (Pinel 2009, p. 348).  Colman (2008, p. 701) defined sleep as a periodic state of muscular relaxation, reduced metabolic rate, and suspended consciousness. Furthermore, sleep consists of five stages that include REM (rapid eye movement) sleep, followed four separate stages called one, two, three, and four collectively known as NREM (non-rapid eye movement) sleep. Psychologists have developed two theories that explain why animals sleep. Supporters of recuperation theories of sleep argue that wakefulness interrupts the homeostasis of the body and that sleep is a function that addresses this disruption (Pinel 2009, p. 352). In contrast, circadian theories of sleep maintain that sleep is part of a 24-hour internal system (Pinel 2009, p. 352). For example, Cariou, Galy, and Melan (2008) conducted a study assessing the 24-hour variation of alertness levels of workers. They found that during the night shift, heart rates were lower. Specifically, heart rates dropped from a rate of about 84 beats per minute (M= 84.40. SD= 10.11) at 15:00 hours to roughly 73 beats per minute (M= 73.64. SD= 10.59) at 02:00 hours. Evidently, circadian rhythms dictate the wake-sleep cycle of all individuals. Furthermore, circadian rhythms affect individuals not only when they are asleep or awake, but also influence their body physiologically in other ways, such as temperature. This study examined the role of circadian rhythms on sleep. Specifically, it assessed the relationship between sex, temperature, and sleep. Rather than the use of testing involving intrusive apparatus, it was thought possible to gauge an understanding of the relationship among temperature, sex, and sleep through the subjective self-reports of participants.

Despite understanding the physiological effects of circadian rhythms, the relationship between temperature and sleep is complex and fiercely contested. This study attempts to understand this complex relationship. Krauchi, Cajochen, Pache, Flammer, and Wirz-Justice (2006) suggested that thermoregulatory processes are very much implicated in the instigation of human sleep. Furthermore, they maintained that the slow drop in core body temperature and onset of sleep has been observed in various mammals and clearly has its origins in the evolutionary development of circadian rhythms. However, Krauchi and Wurz-Justice (2001) also stated that even though circadian rhythms are essential in the initialisation of sleep, their role in maintaining sleep is questionable. Raymann, Swaab, and Van Someren (2006) suggested that as humans age, disturbances of sleep increase. They continue to argue that one of the main factors of sleep disturbance is critical loss of temperature due to neuronal activity in the brain. In contrast, other studies suggest that ambient temperature exerts a strong influence upon sleeping patterns. 

Kumar, Mallick, and Kumar (2009) found that rats preferred to stay at a temperature of 27 Celsius when allowed to select their own ambient temperature. When the rats stayed at 30 Celsius there was an increase in the length of sleep. Furthermore, they found that different temperatures influenced rapid-eye movement and deep slow wave sleep patterns, suggesting that ambient temperature can influence the quality of sleep experienced by mammals. Although this suggestion relies on conclusions drawn from the use of a lab and non-human participants. Van Someren (2006) suggested that the lab produces unreliable statistics on sleep and temperature but agreed that a stable warm temperature increases length of sleep. He argued that during human habitual sleep, changes in skin temperature, due to environmental factors, rather than core temperature affect length of sleep. He maintained that naturalistic studies show that humans will seek to warm themselves with warm clothing, by curling up, and cuddling.

This study and various others have suggested that manipulation or a change of temperature can influence an individual’s length of sleep. Specifically, Okamoto-Mizuno, Tsuzuki, Ohshiro, and Mizuno (2005) suggested that low ambient temperatures influence the NREM sleep stages and decrease rapid-eye movement. Okamoto-Mizuno et al. (2005) attempted to change the sleeping patterns of nine male participants by using an electric blanket in order to control the temperature. They found that use of an electric blanket resulted in a decrease of sleep stage 1 and rapid eye-movement but made no significant changes to the other sleep stages. In addition to this, Teramoto, Tokura, Ioki, Suho, Inoshiri, and Masusa (1998) established that different room temperatures also affect length of sleep. They conducted an experiment using two conditions. One condition involved a slow increase of temperature followed by a slow decrease over 8 hours. The second condition involved a slow decrease of temperature followed by a slow increase over the same period of time. They found that participants reported having better quality sleep in the second condition.

In an attempt to assess the relationship between temperature and sleep in babies, Bach, Telliez, Leke, and Libert (2000) exposed neonates to slightly cooler temperatures than normal during sleep. They found that there were minor differences between sexes (boys slept longer than girls), but no significant factor between sex, temperature, and length of sleep was found.

Other studies have focused on the idea that lack of sleep can affect body temperature. For example, Vaara, Kyrolainen, Koivu, Tulppo, and Finni (2009) conducted a sleep deprivation study to assess the relationship between lack of sleep and changes in body temperature. They tested participants’ heart rate and body temperature during 60 hours of sleep deprivation at various intervals using an active orthostatic test. They reported that throughout the deprivation, heart rate and body temperature decreased, but blood pressure remained reasonably steady. They concluded that lack of sleep causes physiological changes, specifically in relation to thermoregulation.

Evidently, the relationship between ambient temperature, body temperature, and sleep is therefore a complex one. With studies differing in their opinion of whether sleep affects temperature or whether a change in temperature affects sleep or both, this present study hypothesised that temperature and sex exerted a significant influence an individual’s length of sleep. Additionally, the null hypothesis was that sex and temperature did not significantly influence an individual’s length of sleep.

Method

Participants

The sample consisted of 47 male and 83 female participants, totalling 130 participants overall. The average age of the participants was 37 (M= 37.16. SD= 11.78). The mean average male participant age was 36 (M= 36.7. SD= 13.34). The mean average female participant age was 37 (M= 37.6. SD= 10.74). All participants completed the same online questionnaire.

Materials

Google Docs hosted the multiple-choice online questionnaire, which consisted of consent information and 43 questions. The questions used specifically for this test were sex, temperature rating, and length of sleep. Participants could choose their response for temperature from three answers ranging from ‘too hot’ ‘too cold’ or ‘just about right’.

Design

The study was a quasi-experiment. Specifically to this study, there were two independent variables, which were being monitored: Sex, which consisted of two factors, either male or female, and Body Temperature, which consisted of three factors, either “too hot”, “too cold” or “just right”. These were compared to a dependent variable, the number of hours of sleep participants reported.

Procedure

Participants were required to read through a brief paragraph that informed them their participation was anonymous and were then asked to give their consent. They were then required to answer 43 questions to complete the survey. Upon completion, participants were informed their answers were being kept confidential and would be used in the final report.

Results

  

 

Value Label

N

Sex

1

Male

47

2

Female

83

Body Temperature

1

I was too hot

18

2

I was too cold

10

3

I was just right

102

Table 1. Between-Subjects Factors

Figure 1 shows that overall, a large majority of participants felt their sleep temperature was just right. However, 18 suggested they were too hot, and 10 reported being too cold.

Descriptive Statistics

Sex

Body Temperature

Mean

Std. Deviation

N

Male

I was too hot

6.8333

1.16905

6

I was too cold

7.8750

1.03078

4

I was just right

7.1514

1.79453

37

Total

7.1723

1.67224

47

Female

I was too hot

8.3750

1.44796

12

I was too cold

6.8333

1.72240

6

I was just right

6.9692

2.01197

65

Total

7.1627

1.96831

83

Total

I was too hot

7.8611

1.52244

18

I was too cold

7.2500

1.51383

10

I was just right

7.0353

1.92890

102

Total

7.1662

1.86008

130

Table 2. Dependent Variable: Number of Hours Slept - Mean Average of Hours Slept and Standard Deviation.

Figure 2 displays the mean averages of hours slept of male and females and their temperature. Males who felt hot recorded less hours than males who felt just right or too cold (M= 6.83. SD= 1.16). In contrast, females who felt cold recorded fewer hours sleep than those who felt just right or too hot (M= 6.83. SD = 1.72). However, women who felt too hot recorded the longest length of sleep (M= 8.37. SD= 1.44). Overall, participants who felt too hot recorded the longest length of sleep (M= 7.86. SD= 1.52), followed by participants who felt too cold (M= 7.25. SD= 1.51), and finally participants who felt just right (7.03. SD= 1.92).

Tests of Between-Subjects Effects

Source

Type III Sum of Squares

df

Mean Square

F

Sig.

Corrected Model

23.404a

5

4.681

1.372

.239

Intercept

2734.930

1

2734.930

801.876

.000

sex

.143

1

.143

.042

.838

Body temperature

4.455

2

2.227

.653

.522

sex * body temperature

12.880

2

6.440

1.888

.156

Error

422.923

124

3.411

 

 

Total

7122.315

130

 

 

 

Corrected Total

446.326

129

 

 

  

a. R Squared = .052 (Adjusted R Squared = .014)

 

 

 

Table 3. Dependent Variable: Number of Hours Slept - Two-way analysis of variance (ANOVA)

A two-way analysis of variance (ANOVA) was performed to analyse the relationship between sex, body temperature, and sleep and the interaction between sex and body temperature. Evidently, sex is not a significant factor upon the number of hours a participant sleeps [F(1,129)=.042;p>.838]. Furthermore, body temperature is also not a significant factor of the length of sleep reported [F(1,129)=.653;p>.522]. As well, there is no significant interaction between body temperature and sex [F(1,129)=1.888;p>.156].

Discussion

Evidently, there is some difference between the lengths of sleep between and within the sexes. Males who felt too cold slept more than other males. In contrast, males who felt too hot slept less than other males in the groups. Additionally, females who felt they were too hot slept more than other females. Furthermore, females who felt they were too cold slept less than females in the other groups. Overall, men slept marginally more than women. Further, participants who felt hot slept marginally more than any other participants from any other group. Therefore, it is possible to conclude that there is some slight variation between the sexes and their reported temperatures. However, the differences are so marginal it is unlikely these differences would be replicated in other studies. Yet, as the majority of participants felt just right, it is reasonable to conclude that these findings support the theory of Van Someren (2006), who suggested that humans actively seek to maximise their length of sleep by staying comfortable.

Therefore, this study found that there was no significant relationship between sex, temperature, and the interaction between these factors on the length of sleep. This may be because the study relied upon the self-evaluations of participants, which were subjective in nature. Such subjectivity cannot provide a clear answer compared to actually monitoring the physiological changes, such as temperature of participants as they sleep. Despite this, it does offer some interesting findings regarding how the participants felt, which may provide an important psychological aspect to how an individual rates their own temperature and sleep. This study rejects the experimental hypothesis and accepts the null hypothesis that temperature is not a significant influence upon length of sleep.

To some extent these findings support the conclusions reached by Bach et al. (2000) that there is very little influence of such factors upon the length of sleep. It may be possible that from birth to adulthood there is very little difference between the sexes, and any marginal change is due to factors mentioned by Raymann et al. (2006), such as the effect of aging on neuronal activity. This study is unable to make such strong conclusions, given the limitations of the experiment.

Future studies could monitor the subjective responses of participants over a long period of time, such as years or months. A longitudinal study such as this could provide more evidence of a relationship between sex, temperature, and length of sleep. Additionally, such studies could assess these factors over a long period of time while monitoring participants of different ages to examine the different possible changes of body temperature and sleep patterns throughout adolescence or old age. Future sleep studies might monitor temperature in a manner that does not rely solely upon the subjective responses of participants, as was the case in the online questionnaire used in this study. Such studies would be able to provide conclusive evidence of the relationship between sex, temperature, and length of sleep. Integration between the monitoring of temperature and the subjective responses of participants, in a similar manner to the experiment conducted by Teramoto et al. (1998), could also assess the relationship between actual temperature versus perceived temperature during sleep and their influence upon the length of sleep.

Further, cross-cultural studies might assess whether there is a universal ideal sleep temperature, given the various climates in which individuals sleep. The present study was limited to participants located mostly in Northwest Europe. A cross-cultural study could examine the different self-reports of perceived temperature during sleep of individuals in two contrasting climates. Furthermore, such findings may support the work of Kumar et al. (2009) and Okamoto-Mizuno et al. (2005) who found that external temperatures such as room temperature could affect sleep. Additionally, future studies could introduce other variables, replicating studies by Okamoto-Mizuno et al. (2005) by controlling the participant’s temperature through the use of electric blankets or other similar devices. Such studies could also continue to assess the affect of temperature on sleep.

Summary

Essentially, this study found that between and within sexes, perceived temperature exerted a marginal influence on the length of sleep. However, it also found that neither sex nor temperature were significant factors to conclude that they directly influence the length of sleep in a substantial manner. Despite the fact that it did not concur with previous research, this study did provide an example of how future studies could utilise the subjective responses of participants in a manner that would draw out stronger conclusions regarding the relationship between temperature and length of sleep. It is evident that the circadian rhythms, no matter how they are studied, are profound in their silent influence over all animals. Ongoing research has much more to learn about the complex nature and origins of the circadian rhythms. Such future conclusions may even expand human understanding of our place within the evolutionary perspective of life and assist those who suffer from the multitude of sleep disorders, which blight many lives.

 

References

Bach, V., Telliez, F., Leke, A., and Libert, J.P. (2000). Sex-related sleep differences in neonates in thermoneutral and cool environments. Journal of Sleep Research. 9 (3), 249-254.

Cariou, M., Galy, E., and Melan, C. (2008). Differential 24-hour variation of alertness and subjective tension in process controllers: investigation of the relationship with body temperature and heart rate. Chronobiology International. 25 (4), 597-609. doi: 10.1080/07420520802261838

Colman, A. (2008). Oxford dictionary of psychology. London: Oxford Press.

Krauchi, K., and Wirz-Justice, A. (2001). Circadian clues to sleep onset mechanisms. Journal of Neuropsychopharamacology. 25 (5), 92-96.

Krauchi, K., Cajochen, C., Pache, M., Flammer, J., and Wirz-Justice, A. (2006). Thermoregulatory effects of melatonin in relation to sleepiness.
Chronobiology International. 23 (1), 475-484. doi: 10.1080/07420520500545854

Kumar, D., Mallick H., and Kumar, V., (2009). Ambient temperature that induces maximum sleep in rats. Physiology and Behaviour. 98 (1), 186-191. doi: 10.1016/j.physbeh.2009.05.008

Okamoto-Mizuno, K., Tsuzuki, K., Ohshiro, Y., and Mizuno, K. (2005). Effects of an electric blanket on sleep stages and body temperature in young men. Journal of Ergonomics. 48 (7), 749-757. doi: 10.1080/00140130500120874

Pinel, J. (2009). Biopsychology. Boston: Pearson.

Raymann, R., Swaab, D., and Van Someren, E. (2006). Skin deep: enhanced sleep depth by cutaneous temperature manipulation. Brain. 131 (2), 500-513. doi:10.1093/brain/awm315

Teramoto, Y., Tokura, H., Ioki, I., Suho, S., Inoshiri, R., and Masusa, M. (1998). The effect of room temperature on rectal temperature during night sleep. Journal of Thermal Biology. 23 (1), 15-21.

Vaara, J., Kyrolainen, H., Koivu, M., Tulppo, and M., Finni, T. (2009). The effect of 60 hour sleep deprivation on cardiovascular regulation and body temperature. European Journal of Applied Psychology. 105 (3), 349-444. doi: 10.1007/s00421-008-0921-5

Van Someren, J.W. (2006). Mechanisms and functions of coupling between sleep and temperature rhythms. Progress in Brain Research. 153, 309-324.


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