Our results suggest that individuals with insomnia have a worse practice of SH in comparison to good sleepers; we also found that when insomnia is comorbid with major depression the SH practice is even worse. Interestingly, although poor practice of SH showed a moderate relationship with insomnia symptoms and poor sleep quality in the whole sample, only in patients with PI the association remained as significant but weak.
Our results are consistent with those of early  and recent studies  that have found insomnia subjects practice less the SH rules than good sleepers; but our results also differ from findings of some other studies . A possible explanation for this disagreement is the variable definition of SH used in the studies. Investigations that have found a significant association between insomnia and poor SH practice (including this one) have used more comprehensive instruments to measure SH. In support of this view are the findings of Gellis and Lichstein who using a 19 item SH instrument found that poor sleepers engaged significantly more frequent in poor sleep SH practices than good sleepers .
Sleep hygiene recommendations lists are quite variable. There are numerous lists, with more or less SH rules and there is no consensus about essential practices or a minimal list. For example, the Hauri’s original list  shows some differences from his own updated list  and also from the maladaptive practices included in the inadequate sleep hygiene category of the International Classification of Sleep Disorders 2 [3, 22]. Moreover, some of the SH recommendations may overlap with the more clearly defined interventions such as stimulus control or sleep restriction therapies.
In this sense, the study of isolated SH practices or SH dimensions may shed light on the active ingredients of SH. We found that patients with insomnia, either primary or comorbid with major depression, had a worse practice in all SH dimensions than good sleepers. However, although good sleepers had a better practice in all SH domains, only sleep environment domain and arousal related behaviors showed a weak but significant association to sleep quality. Similarly, in MDD patients only arousal related behaviors had a weak association with sleep quality, even though MDD group had the worst practice of SH rules. This suggest that SH practice has a small contribution to the sleep of GS and MDD individuals. Only in the PI group, the practice of arousal-related behaviors was moderately associated to insomnia and sleep quality.
The arousal-related behaviors dimension of SH was the only one that showed a consistent, significant relationship with sleep quality and more importantly it was the main predictor of insomnia severity and poor sleep quality. This finding is consistent with observations of Gellis and Lichstein who found that poor sleepers presented with more worries, plans or thoughts about important matters in bed than good sleepers ; and also, it concurs with results of Yang et al. who using the SH practices scale identified that practice of maladaptive arousal related behaviors was the only one significant difference between insomnia subjects and good sleepers . The contribution of arousal-related behaviors to insomnia severity is not a surprise; in fact, is consistent with the physiologic, cognitive, and emotional hyperarousal state associated with insomnia which is one of the targets of cognitive behavioral therapy for insomnia (CBT I), including comorbid insomnia with major depression .
Although we found that the presence of major depression was associated with a worse practice of SH in general and in all SH domains in comparison with good sleepers, the lack of significant relation of SH with insomnia scores suggests that the contribution of SH to insomnia severity in major depression might be negligible.
Even when the evidence about the poorer practice of SH by individuals with insomnia is inconclusive, and some reports have informed about its lack of efficacy as a monotherapy, SH education remains as one of the interventions included in multicomponent therapies. This might be due, at least in part, to its popularity and acceptance. Sleep hygiene is probably the most popular behavioral insomnia approach and some studies have found that patients prefer it to other therapies . But it is also possible that SH is not lacking of effects on insomnia symptoms. A recent systematic review has shown that although SE is less efficacious than CBT I, treatment with SH is associated with improvement of several sleep indexes . Considering our results, the correction of arousal related behaviors might be the main mechanism underlying the mild sleep improvement produced by SH. Taken together, the SH’s popularity, its acceptance and its possible effects on arousal related behaviors might be enough reasons to maintain SH in multicomponent therapies. To say the least, SH may serve as an entry step or a as an induction intervention to more efficacious therapies. This speculation deserves future research.
On the contrary, if the contribution of inadequate SH to insomnia is just through the practice of maladaptive arousal related behaviors which can be properly treated with other interventions, future investigations should consider the exclusion or substitution of SH in multicomponent therapies.
There are several limitations to this study that should be acknowledged. We did not include a sample of depressed patients without insomnia; consequently, our results cannot be generalized to this infrequent expression of major depression. Although the instrument we used to assess SH showed a satisfactory reliability coefficient, the subscale of eating/drinking behaviors had a slightly low coefficient of internal consistency; therefore, the significant findings associated with this SH domain could be questionable. Nevertheless, our results are in line with reports of a higher use of sleep disrupting substances among poor sleepers [6, 26]. Likewise, although we tried to study the association of a set of behaviors with insomnia, we did not evaluate isolated behaviors or dimensions, therefore some SH rules/domains might be operating through combined mechanisms. Finally, our results do not inform whether inappropriate SH practice is a predisposing, precipitant, or perpetuating factor, which is of particular relevance in the context of Spielman’s model of insomnia .