ABSTRACT
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Abstract: In relation to individual differences in the habitual duration of sleep, a distinction can be established between subjects having a short sleep pattern (6 hours or less of sleep per night), subjects with an intermediate sleep pattern (between 7 and 8 hours of sleep), and subjects with a long sleep pattern (more than 9 hours of sleep). The reason for these individual differences in sleep duration is unknown. Diverse studies have been carried out in an attempt to understand if psychological or physiological differences exist in people with distinct sleep patterns. Recently, it has been demonstrated that sleeping less and, paradoxically, sleeping more than the sleep quantity associated with the intermediate sleep pattern (7-8 hours) has a negative impact on physical health. On the contrary, studies about possible psychological differences between different sleep patterns are almost nonexistent. Some studies that analyze variables regarding vigilance suggest that subjects with a long sleep pattern have a poorer performance in tests of vigilance than subjects who have a short sleep pattern. In turn, subjects with short sleep pattern appear to have more academic efficiency problems and appear to show a more depressed mood state than the subjects belonging to the other sleep pattern groups. One aspect that has been scarcely analyzed, with the exception of the classic works by Hartmann and Hicks in the 1970's, is if sleep patterns differ according to personality characteristics. The dimensions of personality which have received more attention have been extraversion and neuroticism, and none of the majority of studies has observed any significative differences in function of sleep patterns. Nevertheless, in the case of neuroticism, results are contradictory and there exist also reports that observe differences in sleep pattern function. It is important to emphasize that in these studies the quantity of sleep was not considered along with other essential aspects of sleep such as quality. Perhaps this aspect could explain a part of the inconsistent findings in the literature. On the other hand, psychoticism, which along with extraversion and neuroticism constitutes the third big dimension of the known tripartite model of personality, has been the least investigated personality dimension. Again, no work exists which analyzes the relations between the pattern of sleep and the dimension of personality of cognitive limits more recently proposed by Hartmann. The present study is a part of a wider investigation, the objective of which is to analyze the relations between the subjective quantity and quality of sleep and psychological variables in healthy individuals. This paper is centered on the influence of the pattern of sleep (short, intermediate, and long), the subjective quality of sleep (high, medium, or low) and the possible interaction between both factors in the personality dimensions of neuroticism, psychoticism, and cognitive limits. The sample was composed of 125 healthy students (110 women and 15 males) with ages ranging from 18 to 26 years old. The participants were selected according to their responses to a sleep questionnaire created for this purpose, which explored the habits of sleep, the state of medical health, past and present psychological condition, and possible use of medication. All the subjects selected showed good medical and psychological health, they did not use any type of medication, nor did they belong to any extreme morning or evening type of circadian rhythm. Each subject had a regular bedtime hour between 11:30 p.m. and 2:30 a.m. and waking hour between 7:30 a.m. and 10:30 a.m. The subjects selected were divided into three groups in accordance with the number of hours they habitually slept in order to feel good during the day: 1. subjects with short sleep pattern (n=20), 2. subjects with intermediate sleep pattern (n=82) and finally, 3. subjects with long sleep pattern (n=23). Additionally, other three groups were established within each of the sleep patterns considering if the quality of sleep was high, medium, or low. In short sleep pattern group the quality of sleep reported as high, medium, and low was 25%, 40%, and 35%, respectively. These percentages were 42.68%, 43.9%, and 13.41% in the group with an intermediate sleep pattern; and 30.43%, 52.17%, and 17.39% in the group with a long sleep pattern. The personality dimensions of neuroticism and psychoticism were evaluated with The Eysenck Personality Questionnaire (EPQ-A). The cognitive boundaries were evaluated with The Boundary Questionnaire (BQ). In addition, subjects completed the Beck Depression Inventory (BDI) and the Beck Anxiety Inventory (BAI) (which have not been taken into consideration here). The criteria of exclusion were a score higher than 18 on the BDI or the BAI and a score higher than 70 on the dimensions of neuroticism and psychoticism. These last exclusions were established to make assure the subjects were free of psychological dysfunction. Two-way analyses of variance (ANOVAs) were performed to assess the effects of the quantity of sleep (short, intermediate, or long sleep pattern), and the subjective quality of sleep (high, medium, or low) and the possible interaction between both factors in the case of each variable. The Levene test was used to examine variance homogeneity. Likewise, the Scheffé Test (for equal variances) and the Tamhane Test (for unequal variances) were used as post hoc contrast statistics. The results showed the dimension of neuroticism was influenced by subjective sleep quality, but not by habitual sleep duration. Subjects with a poor subjective sleep quality scored higher on neuroticism (15.14) than those who had a medium (13.23) or good (9,96) sleep quality. Contrarily, the personality dimension of psychoticism was influenced by sleep quantity, but not quality. Subjects with a low sleep pattern scored slightly higher in psychoticism (2.57) than those with intermediate (1.52) or short (1.25) sleep patterns. The dimension of cognitive boundaries was not related with any of these aspects. There was not any significant interaction between sleep quantity and sleep quality for the analyzed variables. This result highlights the need to evaluate sleep quantity as well as sleep quality, treating them as two relatively independent measures that provide complementary information. The highest scores of neuroticism of the group with the worse quality of sleep are consistent with recent reports showing that being worried or anxious disturbs the normal appearance of slow wave sleep (phases 3 and 4). The expression of this sleep phase is psychologically linked with sleep quality. On the other hand, it may be the case that the highest scores in psychoticism obtained by the subjects with long sleep pattern relate with the extra quantity of REM they obtain by sleeping a greater number of hours. This phase of sleep has been associated with mood regulation and psychological balance. In polysomnographic studies, subjects with long sleep pattern are characterized as having a greater quantity of phase 1, 2, and REM sleep and less quantities of slow wave sleep than the other sleep patterns. However, the present data are correlational and not casual. Thus, the mechanisms which could be influencing in the observed relationships are unknown. Similarly, it is unclear how sleep pattern differences might translate into psychological or biological changes which may affect personality, mood, or health. Future longitudinal research, including objective sleep measurements in healthy subjects, as well as in subjects with sleep disorders of different degrees, may contribute to the clarification of these mechanisms. In any case, sleep seems to be an excellent indicator of several psychological characteristics and so the consequences associated with models which deviate from the intermediate sleep pattern deserve to be taken seriously. It is also important to develop preventive and educational initiatives to optimize our sleeping habits.
ABSTRACT
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Abstract: The areas in which interesting connections can be established between sleep and health are increasingly numerous. With reference to the habitual sleep duration, usually there is a distinction between subjects being mentioned as having short sleep pattern (sleeping 6 hours ot less per day), subjects with intermediate sleep pattern (sleeping 7-8 houts per day) and subjects with long sleep pattern (sleeping 9 ot more hours per day). The reason for these individual differences in sleep duration is unknown and it is still debatable as to wherher a period of 7 ot 8 hours of sleep is, in fact, ideal in terms of physical and mental well being. Evidence found in the last few years shows that sleeping more time, ot less, than associated to the intermediate sleep pattern (7-8 hours), appeats to have adverse consequences on physical health. In different studies, the subjects with intermediate sleep pattern have a better physical health, a minot mottality tisk and, fot example, a minot tisk fot developing diabetes ot coronaty events. On the other hand, there are very few investigations concerning the possible psychological differences between sleep patterns and the results are inconsistent. Also, the current line of investigation focuses on the sleep quantity parameter without simultaneously evaluating other televant sleep aspects, such as sleep quality. The negative impact on health of a poor sleep quality is better understood, but has been investigated almost exclusively in subjects with sleep disotdets. In order to better undetstand the relationship between sleep and psychological well being it is necessary to investigate the joint effect of sleep quality and sleep quantity without a direct influence of clinical alterations. Furthermore, the difference between sleep quantity and sleep quality is important if a more complete analysis of this topic is to be teached. The present work is the first of two that analyze the relation between subjective sleep quantity and quality, and psychological variables in healthy subjects. This paper focuses on the influence of the sleep pattern (shott, intermediate and long sleep pattern), the subjective sleep quality (high, medium ot low sleep quality), and the possible interaction between both factors on the anxiety and the depressed mood state. All study participants were selected considering their responses to a sleep questionnaire created for this purpose, which exploted sleep habits, past and present medical and psychological conditions, and medication consumption. The final sample was composed of 125 healthy students (110 women and 15 men) aged between 18 and 26 years. The selected subjects presented good medical and psychological health and neither consume any type of medication non had an extteme citcadian type (morning-type ot evening-type). Each subject had a common bedtime hour between 11:30 p.m. and 2:30 a.m. and a wake time hour between 7:30 a.m. and 10:30 a.m. The sample was divided in the following way: 1) Subjects with a short sleep pattern (n=20), 2) Subjects with an intermediate sleep pattern (n=82), and 3) Subjects with a long sleep pattern (n=23). Thtee subgroups wete fotmed within each sleep pattetn in function of the subjective sleep quality, consideted as being high, medium ot low. These petcentages wete 25%, 40% and 35%, tespectively, in the gtoup with shott sleep pattern; 42.68%, 43.9% and 13.41% in the group with intermediate sleep pattern; and 30.43%, 52.17% and 17.39% in the group with long sleep pattern. The anxiety and the deptessed mood state were evaluated with the Beck Anxiety Inventory (BAI) and the Beck Depression Inventory (BDI), respectively. In adittion, subjects completed the Eysenck Personality Questionnaire (EPQ)(which has not been taken into consideration here). Subjects with BAI ot BDI punctuations highet than 18 points ot with scores over the centil 70 in neutoticism and psychoticism were excluded in order to guatantee that the sample was ftee of psychological dysfunction. Two-way ANOVAs were performed to examine the effects of sleep quantity (short, intermediate ot long sleep pattern) and subjective sleep quality (high, medium ot low sleep quality) as well as their interaction on anxiety and depressed mood state. The Levene test was used to examine vatiance homogeneity. The Scheffé test (fot equal vatiances) and the Tamhane test (fot unequal variances) were used as post hoc contrast statistics. The results showed that the BAI punctuations were influenced by subjective sleep quality but not by habitual sleep duration. Those subjects satisfied with their sleep had less anxiety symptoms (8.18) than those who estimated their sleep as being of lowet quality (14.34). There were no differences as to anxiety between the group with medium and low sleep quality. The BDI scotes were influenced by the sleep quantity as well as the quality of sleep. The subjects with short sleep pattern had highet punctuations on depressed mood (10.75) than those with medium (6.10) or long (6.04) sleep pattern. With reference to sleep quality, subjects with high subjective sleep quality had lowet punctuations on depressed mood (3.51) than those with medium (7.73) ot low (11.64) sleep quality. Depressed mood is the variable which holds a closet relationship with sleep processes, as can be seen in its relations with sleep quantity as well as subjective sleep quality, even the sample was non-clinical. Anxiety is related with sleep quality. There is not any significant interaction between sleep quantity and sleep quality for the analyzed variables. This results highlight the need to evaluate sleep quantity as well as sleep quality, due to both being relatively independent measutes that ptovide complementaty infotmation. The mechanisms that can be mediating in the observed relationships are uncleat. Note that the data fot this type of study is correlational and not causal. Sleep quality seems to depend on the expression of slow wave sleep (phases 3 and 4). Recent studies show that being wottied ot anxious disturbs the normal appeatance of there phases, which could be related to the findings found in the current study. In relation to sleep duration, it is possible that the negative impact of a short sleep pattern on mood be related with some type of accumulated sleep deprivation. The reasoning is even more uncleat in long sleep pattern subjects and maybe related to the extra REM sleep that typically occuts when a person sleeps more than 7-8 hours. In order to better understand this series of relationships it is necessary to carry out longitudinal investigations with objective measures in healthy subjects as well as in subjects with sleep disorders of different degrees, and should include subjects with different ages (children, adults, etc.). It is important to consider the consequences associated to the deviant models of sleep duration and optimum sleep quality, making it necessary to encoutage preventive and educational measutes designed to improve out sleep habits. This assumption is not incompatible with a cettain individual variability that may exist with reference to sleep duration, albeit within cettain boundaties (e.g. in young people from 6 to 9 hours) which will come to be included in the intermediate sleep pattern.