Sleep disorders constitute one of the most relevant health problems in Occidental societies. Between 30-40% of the population suffers from insomnia, whereas 1-10% suffers sleep apneas, and around 60% of shift workers report disturbances in the circadian rhythm. The importance of a good sleep quality is not only fundamental in determining health, but is also a propitiatory element for a good quality of life. Sleep quality is not only defined as a good night sleep. It also includes a good daytime functioning (the adequate level of attention needed to complete different tasks). Sleep disorder incidence rates in different populations need to be studied in order to better understand this daytime functioning and its determining factors. To reach this objective, and because of difficulties involved in administering a polysomnographic evaluation to detect sleep quality, self-report measures are used in the majority of the cases (for example, the Pittsburg Sleep Quality Index). From a behavioral evaluation point of view, sleep is made up of four different dimensions: circadian time, that is, the time of day when sleep is located, the organism's intrinsic factors (age, sleep, sleep patterns), a subject's facilitating and inhibiting behaviors, and the environment in which the subject sleeps. As sleep hygiene affects these last two dimensions, in our study we focus on the inhibiting behaviors (psychoactive substance consumption). The present investigation uses the Pittsburg Sleep Quality Index to analyze the subjective sleep quality in a sample of 716 university students (584 females and 132 males). The investigation also evaluates the effects of alcohol, caffeine, and tobacco consumption on sleep quality. The Pittsburg Sleep Quality Index provides a total sleep quality score and partial scores for seven different components: subjective sleep quality; sleep latency; sleep duration; habitual sleep efficiency; sleep dysfunctions; use of hypnotic medication; and daytime dysfunction. The score for each one of the seven components oscillates between zero (absence of difficulty) and three (severe difficulty). The total score ranges from 0 to 21, with a cut-off point of 5, which differentiates between good and bad sleepers. This instrument reveals satisfactory psychometric data in the Spanish population, demonstrating an internal consistency which oscillates between 0.67 in a student sample and 0.81 in a clinical sample. A sensitivity of 88.63% and a specificity of 74.19% is obtained when analyzing the validity. The results show that approximately 30% of the sample presents a poor sleep quality, an excessive latency, and a poor sleep efficiency. These results suggest that difficulties in falling asleep characterize a poor sleep quality in younger subjects, whereas nighttime and premature awakenings are more common among older subjects. The total scores for the Pittsburg Sleep Quality Index reveal that 60.33% of the sample score higher than five, therefore defining these subjects as poor sleepers. The only difference found between males and females is observed in the hypnotic consumption component, in which women presented higher scores. The absence of differences in sleep quality between men and women could be due to the sample median age (20.92 years), since the poorest sleep quality in women is more evident as age increases. However, our data support evidence that the use of hypnotics is more frequent in women than in men. It is also demonstrated that an excessive use of alcohol, caffeine, and nicotine provokes a variety of sleep disturbances: an increase in sleep latency, nocturnal awakenings, a reduction in slow sleep waves, a reduction in the total sleep time, and a poor self-report. However, the effect of these substances on sleep in a social consumption context (non-excessive) is not understood yet. In this study, we have defined social consumers as those subjects who daily drink between two and four alcoholic drinks or two and four cups of coffee, or who daily smoke between 20 and 30 cigarettes. The results showed that a non-excessive daily consumption of alcohol, caffeine, and tobacco provokes a poor sleep quality, a greater sleep latency, a greater number of sleep disturbances, and a greater daytime dysfunction. This indicates that the characteristics and quality of sleep in subjects who do not excessively consume alcohol, caffeine, and tobacco are very similar to the characteristics and sleep quality of substance dependent subjects. Another relevant fact is that the effects that we have found when using self-report measures are similar to those found through a polysomnographic evaluation in subjects dependent on psychoactive substances. This reveals the need to control the consumption of these substances in order to maintain an adequate sleep quality. Furthermore, this demonstrates that poor sleep quality should also be added to the diverse negative effects of an excessive psychoactive substance consumption.
