Resumen:

La duración habitual de sueño varía notablemente de unas personas a otras sin que se tenga claro a qué se deben tales diferencias. Suele establecerse una distinción entre los denominados sujetos con patrón de sueño corto (duermen seis horas o menos al día), los sujetos con patrón de sueño intermedio (duermen entre 7-8 horas al día), y aquéllos con patrón de sueño largo (duermen más de nueve horas al día).

En los últimos años se han acumulando pruebas respecto a que el dormir menos tiempo -y también, paradójicamente, más tiempo del asociado al patrón de sueño intermedio- parece tener consecuencias adversas pata la salud física a diversos niveles. Por el contrario, los estudios sobre las posibles diferencias psicológicas entre los patrones de sueño son escasos e inconsistentes. Además, la investigación al respecto se ha centrado en el parámetro de duración sin evaluar simultáneamente otros aspectos del sueño que son relevantes como la calidad del mismo. El impacto negativo que ejerce sobre la salud una pobre calidad de sueño, se conoce mejor, peto este aspecto ha sido analizado casi exclusivamente en muestras de sujetos con trastornos del sueño. Pata una mejor comprensión de la relación entre sueño y bienestar psicológico se hace necesario estudiar el efecto conjunto de la calidad y la cantidad de horas de sueño sin la influencia directa de alteraciones clínicas.

El presente trabajo analiza la influencia del patrón de sueño (corto, intermedio y largo), la calidad de sueño (alta, media y baja) y la posible interacción entre ambos factores sobre la ansiedad y el estado de ánimo deprimido.

Participaron en la investigación 125 estudiantes sanos (110 mujeres y 15 varones) de 18 a 26 años, seleccionados mediante un cuestionario de sueño elaborado pata este propósito que explotaba sus hábitos de sueño y controlaba que los sujetos no tuvieran problemas médicos, psicológicos o estuvieran tomando fármacos. La muestra se distribuía del siguiente modo: 1) Sujetos con patrón de sueño corto (n=20), 2) Sujetos con patrón de sueño intermedio (n=82), y 3) Sujetos con patrón de sueño largo (n=23). A su vez, dentro de cada uno de los patrones de sueño, se establecieron tres subgrupos en función de si la calidad subjetiva de sueño eta alta, media o baja.

La ansiedad y el estado de ánimo deprimido se evaluaron con los Inventarios de Ansiedad y Depresión de Beck (BAI y BDI, respectivamente). Se excluyó a los sujetos con puntuaciones superiores a 18 en estos instrumentos a fin de intentar garantizar que la muestra no presentara alteraciones psicológicas.

Se efectuaron ANOVAs para examinar si el patrón de sueño, la calidad de sueño o la interacción de ambos factores tenían algún efecto en la ansiedad o en el ánimo deprimido. Los contrastes post hoc se realizaron con la prueba de Scheffé o de Tamhane. Los resultados mostraron que la ansiedad en el BAI eta influida por la calidad de sueño peto no por su duración. Los sujetos satisfechos con su sueño presentaban menos ansiedad (8.18) que los que estimaban que su sueño eta de menor calidad (14.34). Las puntuaciones en el BDI se hallaron influidas tanto por la cantidad como por la calidad de sueño. Los sujetos con patrón de sueño corto alcanzaron cifras más altas en la variable estado de ánimo deprimido (10.75) que los que tenían un pattón de sueño medio (6.10) o latgo (6.04). Por lo que se refiere a la calidad de sueño los sujetos con alta calidad calificaron más bajo en la variable ánimo deprimido (3.51) que los que tenían una calidad de sueño media (7.73) o baja (11.64).

El ánimo deprimido es la variable que guarda una relación más estrecha con los procesos de sueño como lo indica el hecho de que, incluso en una muestra no clínica, sus puntuaciones son moduladas tanto por la cantidad como por la calidad de sueño. La ansiedad sólo resulta afectada por la calidad de sueño. En ninguna de las variables analizadas existe una interacción significativa entre cantidad y calidad de sueño lo que pone de manifiesto la necesidad de evaluar ambos aspectos ya que se trata de dos medidas relativamente independientes que proporcionan información complementaria.

Se ofrecen algunas hipótesis sobre los mecanismos que pueden estar mediando en las relaciones observadas. Se destaca que es importante tomar en serio las consecuencias asociadas con los modelos desviados de la duración y de la calidad óptima del sueño, y es necesario fomentar iniciativas preventivas y educativas destinadas a mejorar nuestros hábitos de sueño.

Palabras clave: Duración habitual del sueño; calidad subjetiva de sueño; ansiedad; estado de ánimo deprimido

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.

Key words: Habitual sleep duration; subjective sleep quality; anxiety; depressed mood state