2006, Number 2
Influence of subjective sleep quantity and quality on anxiety and depressed mood state
Miró E, Martínez P, Arriaza R
Full text
Language: Spanish
References: 31
Page: 30-37
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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 or less per day), subjects with intermediate sleep pattern (sleeping 7-8 hours per day) and subjects with long sleep pattern (sleeping 9 or more hours per day). The reason for these individual differences in sleep duration is unknown and it is still debatable as to whether a period of 7 or 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, or less, than associated to the intermediate sleep pattern (78 hours), appears to have adverse consequences on physical health. In different studies, the subjects with intermediate sleep pattern have a better physical health, a minor mortality risk and, for example, a minor risk for developing diabetes or coronary 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 relevant 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 disorders.
In order to better understand 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 reached.
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 (short, intermediate and long sleep pattern), the subjective sleep quality (high, medium or 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 explored 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 extreme circadian type (morning-type or 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). Three subgroups were formed within each sleep pattern in function of the subjective sleep quality, considered as being high, medium or low. These percentages were 25%, 40% and 35%, respectively, in the group with short 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 depressed 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 or BDI punctuations higher than 18 points or with scores over the centil 70 in neuroticism and psychoticism were excluded in order to guarantee that the sample was free of psychological dysfunction.
Two-way ANOVAs were performed to examine the effects of sleep quantity (short, intermediate or long sleep pattern) and subjective sleep quality (high, medium or low sleep quality) as well as their interaction on anxiety and depressed mood state. The Levene test was used to examine variance homogeneity. The Scheffé test (for equal variances) and the Tamhane test (for 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 lower quality (14.34). There were no differences as to anxiety between the group with medium and low sleep quality. The BDI scores were influenced by the sleep quantity as well as the quality of sleep. The subjects with short sleep pattern had higher 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 lower punctuations on depressed mood (3.51) than those with medium (7.73) or low (11.64) sleep quality.
Depressed mood is the variable which holds a closer 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 measures that provide complementary information.
The mechanisms that can be mediating in the observed relationships are unclear. Note that the data for 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 worried or anxious disturbs the normal appearance of these 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 unclear in long sleep pattern subjects and maybe related to the extra REM sleep that typically occurs 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 encourage preventive and educational measures designed to improve our sleep habits.
This assumption is not incompatible with a certain individual variability that may exist with reference to sleep duration, albeit within certain boundaries (e.g. in young people from 6 to 9 hours) which will come to be included in the intermediate sleep pattern.
REFERENCES