Introduction

Inadequate sleep hygiene has been considered one of the several factors contributing to poor sleep and insomnia, including insomnia comorbid with mental disorders (^{Nowell et al., 1997}; ^{Kohn & Espie, 2005}). Sleep hygiene (SH) consists of recommendations aimed at avoiding behavioral practices that interfere with sleep and practicing behaviors that promote good sleep (^{Stepanski & Wyatt, 2003}). However, the study of the association of SH with the sleep of patients with insomnia has yielded mixed results. Whereas ^{Lacks and Rotert (1986)} found that insomniacs adhere less to SH rules than controls, ^{Harvey (2000)} found no differences in the practice of SH rules between insomniacs and control individuals. In a study of SH practices in a population-based sample of insomniacs, ^{Jefferson et al. (2005)} found that subjects with insomnia were more likely to show inadequate SH practices such as smoking, drinking alcohol, napping, and sleeping on weekends in comparison with good sleepers matched by age and sex. In a similar manner, single SH practices (variable sleep length, noise disturbance, going to bed thirsty, and worrying about the ability to fall asleep at bedtime) have been found to predict sleep quality in college students (^{Brown, Buboltz, & Soper, 2002}). ^{Gellis, Park, Stotsky, and Taylor (2014)} reported that inconsistent sleep schedules and behaviors that promote arousal near bedtime were significantly associated to insomnia severity in college students. These last findings suggest that some SH components might have a greater influence on sleep than others.

Nevertheless, few studies have assessed the efficacy of SH as a single treatment for insofigurmnia and their results have not been encouraging. In two studies, SH did not produce significant changes in sleep (^{Friedman et al., 2000}; ^{Engle-Friedman, Bootzin, Hazlewood, & Tsao, 1992}), and only in one study, SH produced a significant improvement of insomnia (^{Schoicket, Bertelson, & Lacks, 1988}).

The practice of SH in insomnia associated to mental disorders has been scarcely studied (^{Kohn & Espie, 2005}) and as far as we know, the practice of SH by depressed patients with comorbid insomnia has not been explored. The study of this population is particularly interesting if we consider, as has been suggested by ^{Stepanski and Wyatt (2003)}, that inadequate SH may be operating when there is a greater predisposition to sleep problems as happens with major depression; and maybe only some SH rules may be contributing to patients´ poor sleep.

In this way, in this study we aimed to compare the practice of SH rules between patients with major depression with comorbid insomnia, primary insomnia, and good sleepers; and to examine the relationship between the practice of SH, sleep quality, and insomnia severity.

Method

Results

One hundred and eighty-two individuals participated in the study: 62 patients with major depressive disorder (MDD), 56 patients with primary insomnia (PI), and 64 good sleepers (GS). While there were no significant gender differences among the groups, patients with PI were significantly older than GS, who, in turn, had significantly more schooling years than PI and MDD patients (Table 1).    

Individuals with MDD had significantly higher scores on ISI and PSQI than PI patients, who, in turn, showed significantly worse scores than GS (Table 2). Age and schooling did not contribute significantly to the difference in ISI (age F(2) = 1.7, p = .17; schooling F(2) = 1.9, p = .14) and PSQI scores (age F(2) = .53, p = .58; schooling F(2) = .45, p = .63). Likewise, patients with MDD had the worst practice of SH measured as a whole; again, age and education did not contribute to this difference (age F(2) = 1.2, p = .29; schooling F(2) = 1.8, p = .16). When the groups were compared in the domains of SH, participants with MDD showed a significantly worse practice of sleep schedule and arousal related behaviors than PI group, but there were not significant differences in drinking/eating and sleep environment domains. Both, MDD and PI groups had significantly higher scores than GS in all SH domains (Table 2).    

In respect to the relationship between SH practice and insomnia, a significant moderate relation between global SH and ISI scores was observed (Table 3). Likewise, all SH domains showed significant positive relations with insomnia. Similar correlation coefficients were observed for the relation between SH, either global or dimensions, and PSQI scores in the whole sample. However, when correlation coefficients were calculated in each group, a different pattern of results was obtained. In GS, there was no significant relation between SH, either global or any dimension, and insomnia severity. In contrast, sleep environment and arousal-related behaviors showed a weak positive relation with sleep quality scores. In the PI group, significant weak correlation coefficients were observed between the practice of SH as a whole and insomnia and sleep quality; only arousal-related behaviors showed a significant moderate relation with insomnia and sleep quality. In the MDD group, there were no significant relations between insomnia and SH; by contrast, arousal-related behaviors showed a significant weak relation to sleep quality.    

The results of the linear regression analyses are shown in Tables 4 and 5. More than a half of the variance in insomnia severity was explained by the model (R² = .58, F (4, 177) = 61.1, p  <  .001). However, only arousal-related behaviors (ß = .79, p  <  .001) and drinking/eating habits (ß = -.17, p  <  .01) significantly contributed to the model. In the second regression analysis, again, 57% of the variance in sleep quality scores was explained by the predictors together (R² = .57, F (4, 177) = 59.4, p  <  .001); but only arousal related behaviors (ß = .77, p  <  .001) and drinking/eating behaviors (ß = -.12, p  <  .05) were significantly associated with sleep quality.    

Discussion and conclusion

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 practice of SH is even worse. 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.

These results are consistent with those of early (^{Lacks & Rotert, 1986}) and recent studies (^{Yang et al., 2010}) that have found insomnia subjects practice less the SH rules than good sleepers; but our results also differ from findings of some other studies (^{Harvey, 2000}). 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 (2009)} who used a 19-item SH instrument and 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 (^{Hauri, 1977}) shows some differences from his own updated list (^{Hauri, 1992}) and also from the maladaptive practices included in the Inadequate Sleep Hygiene category of the International Classification of Sleep Disorders 2 (^{Stepanski & Wyatt, 2003}; ^{American Academy of Sleep Medicine, 2005}). 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 the 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 (2009)} 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. (2010)} who using the SH Practices Scale identified that the 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 (^{Manber et al, 2008}).

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 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 (^{Vincent & Lionberg, 2001}). But it is also possible that SH is not lacking 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 (^{Chung et al, 2017}). 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 (^{Jefferson et al., 2005}; ^{Johnson, Rohers, Roth, & Breslau, 1998}). 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 (^{Spielman, Caruso, & Glovinsky, 1987}).

Our results show that patients with insomnia, either primary or comorbid with major depressive disorder, have a worse practice of SH in comparison with good sleepers. However, the contribution of inadequate sleep hygiene to poor sleep seems to be through the practice maladaptive behaviors related with arousal.