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Psychosomatic Medicine 65:259-267 (2003)
© 2003 American Psychosomatic Society

ORIGINAL ARTICLES

Role of Stress, Arousal, and Coping Skills in Primary Insomnia

Charles M. Morin, PhD, Sylvie Rodrigue, MPs and Hans Ivers, MPS

From Université Laval, Sainte-Foy, Québec, Canada.

Address reprint requests to: Charles Morin, PhD, Professor, Université Laval, École de Psychologie Pavillon F.A.S., Ste-Foy, Québec, Canada G1K 7P4. Email: cmorin{at}psy.ulaval.ca


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
OBJECTIVE: Although stress is often presumed to cause sleep disturbances, little research has documented the role of stressful life events in primary insomnia. The present study examined the relationship of stress and coping skills, and the potential mediating role of presleep arousal, to sleep patterns in good sleepers and insomnia sufferers.

METHODS: The sample was composed of 67 participants (38 women, 29 men; mean age, 39.6 years), 40 individuals with insomnia and 27 good sleepers. Subjects completed prospective, daily measures of stressful events, presleep arousal, and sleep for 21 consecutive days. In addition, they completed several retrospective and global measures of depression, anxiety, stressful life events, and coping skills.

RESULTS: The results showed that poor and good sleepers reported equivalent numbers of minor stressful life events. However, insomniacs rated both the impact of daily minor stressors and the intensity of major negative life events higher than did good sleepers. In addition, insomniacs perceived their lives as more stressful, relied more on emotion-oriented coping strategies, and reported greater presleep arousal than good sleepers. Prospective daily data showed significant relationships between daytime stress and nighttime sleep, but presleep arousal and coping skills played an important mediating role.

CONCLUSIONS: The findings suggest that the appraisal of stressors and the perceived lack of control over stressful events, rather than the number of stressful events per se, enhance the vulnerability to insomnia. Arousal and coping skills play an important mediating role between stress and sleep. The main implication of these results is that insomnia treatments should incorporate clinical methods designed to teach effective stress appraisal and coping skills.

Key Words: insomnia, • sleep disturbance, • stress, • coping skills.

Abbreviations: ANCOVA = analysis of covariance;; ANOVA = analysis of variance;; BAI = Beck Anxiety Inventory;; BDI = Beck Depression Inventory;; CISS = Coping Inventory for Stressful Situations;; DSI = Daily Stress Inventory;; IIS = Insomnia Interview Schedule;; LES = Life Experience Survey;; MANOVA = multiple analysis of variance;; PSAS = Pre-Sleep Arousal Scale;; PSS = Perceived Stress Scale.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Insomnia is a prevalent and costly health problem that is often associated with psychological distress, functional impairments, and reduced quality of life (1). Although significant advances have been made in the treatment of primary insomnia in the last decade (2, 3) , its etiology is still poorly understood. Psychophysiological factors such as stress, anxiety, and hyperarousal are often presumed to play a major role in causing sleep disturbances (4, 5) , but the specific role of those factors in primary insomnia has not been well documented.

Stress is perhaps one of the most common precipitants of sleep disturbance, yet only a few studies have examined systematically its relationship to insomnia (6–8) . Healy et al. (8) reported a significant relationship between major stressful events and the onset of insomnia; specifically they found that insomnia sufferers reported a greater incidence of stressful life events during the year preceding the onset of their insomnia in comparison to previous or subsequent years and in relation to good sleepers. The most frequent stressful events reported by poor sleepers were related to illness and significant losses (eg, death and divorce). A similar study of the relationship between major stressful events and insomnia among elderly individuals (6) found no significant difference in the frequency and in the evaluation of those events between good sleepers and insomnia sufferers; however, there was a significant association between a negative appraisal of stressors and sleep disturbances.

Researchers have also examined the influence of more minor stressful events on sleep. These stressors (eg, arguments with a spouse or job strain) are distinguished from major stressful events by their heightened potential for occurring on a daily basis (9). Rubman et al. (10) found that daily minor stressors correlated with more sleep disturbances among insomnia sufferers. Days filled with more frequent stressors were associated with more time spent awake and poorer sleep quality the following night relative to days with fewer stressors. Another study (11) found that individuals with insomnia reported a greater frequency of negative life events (mostly related to interpersonal relationships), diminished coping skills, and lower self-esteem relative to normal control subjects. Collectively, these data suggest that negative or stressful life events are often associated with sleep disturbances.

It is well recognized that hyperarousal is a core mediating feature of insomnia (4, 5, 12) . Several cross-sectional studies have reported that physiological and cognitive arousals are higher among poor than good sleepers (13–16) . Laboratory studies have also shown that experimentally induced stress at bedtime increases arousal and delays sleep onset (17, 18) . One additional study found that daytime stress was associated with increased bedtime arousal and with more sleep disturbances (19). Despite the apparent link between stress and sleep, it remains unclear whether arousal is a mediating factor of this relationship or an epiphenomenon of nocturnal wakefulness. It is also plausible that the types of strategies used to cope with stress mediate the relationship between stress and sleep. Insomnia sufferers report more difficulty coping with daily stressors than good sleepers (20). This finding has lead to the hypothesis that insomniacs may have deficient coping mechanisms in that they tend to internalize conflicts and ruminate about what they should have done or said in a given situation (5); this rumination would naturally lead to arousal at bedtime. In contrast, individuals who cope more adaptively with daily stress may go to bed in a more relaxed state and sleep better.

According to Lazarus and Folkman (21), coping refers to cognitive and behavioral efforts used to manage external and internal demands that are appraised as taxing or exceeding one’s resources. There are two types of coping strategies, problem-focused and emotion-focused strategies. The perception of control over a stressful situation can determine an individual’s emotional response and predict the most likely coping strategies that will be adopted. In general, emotion-focused coping is more likely to occur when there is an appraisal that nothing can be done to modify harmful, threatening, or challenging environmental conditions. Problem-focused coping is more probable when such conditions are appraised as amenable to change (22). These observations suggest that the types of strategies used by insomniacs to cope with daytime stressors could have an impact on the quality of their sleep at night. In addition, the perception these individuals have of their control over stress could also influence the types of coping strategy used.

The aim of this study was to examine the influence of stress, coping skills, and arousal on sleep patterns of insomniacs and good sleepers. The first objective was to compare individuals with insomnia with good sleepers on several stress- and coping-related variables: 1) frequency and impact of daily minor stressors, 2) frequency and intensity of major stressful events experienced during the last year, 3) coping strategies and perception of control over stress, and 4) presleep arousal state (somatic and cognitive). The second objective was to examine more closely the relationships between daily stress, presleep arousal, and nighttime sleep efficiency and quality. More specifically, it was hypothesized that the relationship of daytime stress to nighttime sleep would be partially mediated by bedtime arousal.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Subjects
The participants were French-speaking community volunteers, aged between 18 and 60 years old, who were recruited through newspaper advertisements. Good sleepers were defined as those participants who had no insomnia complaint and reported to be satisfied with their sleep on a sleep survey. Inclusion criteria for participants with primary insomnia were as follows: 1) a subjective complaint of difficulties initiating and/or maintaining sleep, defined as sleep-onset latency or time awake after sleep onset greater than 30 minutes per night, for a minimum of 3 nights per week; 2) insomnia duration of at least 6 months; and 3) report of at least some daytime impairments (eg, fatigue, impaired functioning, or mood disturbances) attributable to poor sleep. These criteria represent a combination of the diagnostic criteria of the International Classification of Sleep Disorders (23) and the Diagnostic and Statistical Manual of Mental Disorders (24) for chronic primary insomnia. Participants were excluded if there was evidence of 1) another sleep disorder (eg, sleep apnea or periodic limb movements), as suggested by the presence of key symptoms of these disorders; 2) severe depressive or anxiety symptoms, as evidenced by a score greater than 23 on the Beck Depression Inventory (BDI) (25) and/or a score greater than 30 on the Beck Anxiety Inventory (BAI) (26); 3) another medical or psychiatric condition causing insomnia; 4) use of antidepressants or benzodiazepines for a condition other than insomnia; 5) alcohol or substance abuse disorders; 6) currently participating in psychotherapy; or 7) working on a rotating or night shift.

Of the 170 persons who responded to media advertisements, 133 completed a telephone-screening interview. Of those, 51 were excluded because they did not meet inclusion criteria for insomnia or good sleepers (N = 8), age (N = 5) or because of a medical condition (N = 9), a psychiatric disorder, use of psychotropic medications (other than benzodiazepines used for sleep), current psychotherapy (N = 17), alcohol or drug abuse (N = 5), or work on a rotating or night shift (N = 7). After this screening, 82 subjects were eligible for the study and were scheduled for an initial interview. Six did not keep their appointment, and four participants were excluded after the interview because they no longer met criteria (symptoms of another sleep disorder and a score greater than 21 on the BDI). Of the 72 subjects enrolled in the study, 4 dropped out and 1 was excluded because he started a job involving shift work during the course of the study.

A total of 67 persons (38 women and 29 men) completed the study, 40 with insomnia and 27 good sleepers. The average age of participants was 39.6 years (range = 19–60), and the average educational level was 14.8 years (range = 7–20). Fifty-four percent were married, and 67% worked at least part time. In the insomnia group, the average duration of insomnia was 9.8 years (range = 6 months–35 years); there were 6 individuals with sleep-onset insomnia, 15 with sleep-maintenance insomnia, and 19 with mixed sleep-onset and maintenance problems. In addition, 18 were taking medications, and 22 were not. The majority of medicated individuals used benzodiazepines as hypnotics (eg, lorazepam, bromazepam, and temazepam), with an average frequency of 2.8 nights per week (SD = 1.9) and an average dosage of less than 10 mg of diazepam-equivalent per night.

Measures
Screening measures.
The Insomnia Interview Schedule (IIS) (5) is a semistructured interview used to obtain a detailed sleep history and to conduct a functional analysis of precipitating and perpetuating factors of insomnia. It is also designed to screen for other sleep disorders and to determine the relative contribution of psychological, behavioral, environmental, and medical factors. This interview was administered as part of the screening assessment procedure. The BDI (25) and the BAI (26) were used to exclude subjects with severe anxiety and/or depression symptoms. Psychometric properties of the French version of those scales are well established (27, 28) .

Daily self-monitoring measures.
A daily sleep diary (5) was completed on rising each morning. This sleep diary provides subjective estimates of several sleep parameters, including bedtime, sleep-onset latency, frequency of nocturnal awakenings, awakenings duration, wake-up time, rising time, feeling on rising (5-point scale, where 1 = exhausted and 5 = refreshed), and sleep quality (5-point scale, where 1 = very restless and 5 = very sound). The primary sleep variables used in this study were sleep efficiency and sleep quality. Sleep efficiency (ratio of total sleep time divided by time spent in bed and multiplied by 100) is a good quantitative index of the severity of insomnia, whereas sleep quality reflects the individual’s perception of feeling refreshed on rising and of perceived sleep soundness. These variables were computed on a nightly basis, and weekly averages were then computed for the 3 weeks of monitoring. Although sleep diaries do not reflect absolute values obtained from polysomnography, they still represent a reliable and valid index of insomnia (29). They are a practical and economical tool and remain the most often used measure in insomnia outcome research (30, 31) .

The Daily Stress Inventory (DSI) (9) is a 58-item self-report measure that allows a person to indicate events that they have experienced in the past 24 hours. After indicating which events occurred, individuals rate the stressfulness of those events on a Likert scale (1 = occurred but was not stressful, 7 = caused me to panic). Three daily scores are derived for each individual: 1) the number of events that have occurred (FREQ), 2) the sum of the impact rating of these events (SUM), and 3) the average impact rating of the events (AIR; SUM divided by FREQ). Internal consistency and test-retest reliability are adequate, even when considering that stress levels can fluctuate from day to day (9). The DSI was completed daily for 3 weeks. Subjects were instructed to complete it in the evening before going to bed.

The Pre-Sleep Arousal Scale (PSAS) (32) contains 16 items tapping eight symptoms of cognitive (eg, racing mind) and eight symptoms of somatic (eg, muscle tension) arousal experienced at bedtime. Ratings range from 1 (not at all) to 5 (extremely). A total score ranging from 8 to 40 is computed for each subscale; a high score indicates a high arousal. The internal consistency and the test-retest reliability of this questionnaire are adequate (32). Subjects were instructed to complete this scale on arising in the morning along with the sleep diary.

Global and retrospective measures of stress and coping skills.
The Life Experience Survey (LES) (33) is a 57-item self-report measure asking respondents to indicate events they have experienced during the past year. Thirty-four of the events listed in the LES are similar in content to those found in the Schedule of Recent Experience (34). Individuals are also asked to rate, on a 7-point scale (-3 = extremely negative, +3 = extremely positive), the perceived impact of the particular event on their life at the time of occurrence. Four scores are derived from this scale: 1) frequency of events experienced in the past year, 2) intensity of positive events, 3) intensity of negative events, and 4) total score intensity. The LES has acceptable psychometric properties, including internal consistency and test-retest reliability (33).

The Perceived Stress Scale (PSS) (35) is a 14-item self-report scale designed to measure the degree to which situations in one’s life are appraised as stressful. Items represent feelings and thoughts that have occurred in the past month in relation to stressful situations or events. Individuals rate the frequency of each item on a 5-point Likert scale (0 = never, 4 = very often). The higher the total score, the more the person appraises life as unpredictable and uncontrollable. The test-retest reliability of this questionnaire is adequate (35).

The Coping Inventory for Stressful Situations (CISS) (36) is a 48-item self-report measure of coping. The measure is divided into three subscales, each containing 16 items: 1) task-oriented coping, 2) emotion-oriented coping, and 3) avoidance-oriented coping. Only the data related to task- and emotion-oriented coping subscales were analyzed in the present study. These two styles of coping are well validated and have received the most attention in the literature (22, 36–39) . CISS items exemplify different ways of coping, and respondents are asked to rate on a 5-point scale (ranging from 1 = not at all, 5 = very much) how each item is representative of their own ways of coping with stress. The CISS has adequate psychometric properties (36, 39) .

Procedure
After the initial telephone interview, potential subjects were scheduled for an orientation meeting/screening evaluation, which was conducted in small groups and lasted about 11/2 hours. During this session, written informed consent was obtained, and information was provided about the tasks relative to the study. To ensure that participants met inclusion criteria, the IIS (5) was administered in a paper-and-pencil format. Each question was read aloud by the study coordinator, and explanations were provided as needed. After completion of this interview, subjects completed the self-report questionnaires, including the BDI, BAI, LES, PSS, and CISS.

Subjects who still met inclusion criteria after this evaluation were mailed, once a week for 3 weeks, the daily self-monitoring questionnaires (ie, sleep diary, DSI, and PSAS). Subjects were instructed to completed the DSI each evening before going to bed and the PSAS and the sleep diary each morning after rising. To promote compliance with daily monitoring, subjects were asked to return their completed questionnaires on a weekly basis in a prepaid, preaddressed envelope.

Statistical Analyses
Demographics and health habits (ie, sleep medication use, caffeine intake, exercise frequency, and smoking) were investigated as potential covariates using a step-down analysis of covariance (ANCOVA) design (40). To validate the formation of the two groups, one-way (group) analyses of variance (ANOVAs) were conducted on main sleep parameters. Global and retrospective measures were analyzed using one-way (group) ANCOVAs controlling for age. Prospective daily measures (stress, presleep arousal, and sleep) were analyzed as within-subject time-series data. Hence, Pearson correlation coefficients between stress (frequency, sum, and impact), presleep arousal (cognitive and somatic), and sleep (efficiency and quality) were computed for each participant. Using standard meta-analytic procedures (41, 42) , individual Pearson coefficients were transformed into effect-size Zr values and were averaged to test the presence of reliable prospective relationships between stress, arousal, and sleep. To study the contribution of coping on stress, presleep arousal, and sleep, a path model was built from a series of hierarchical linear regressions (43). Alpha level was set at 5% (two-tailed), and all analyses were conducted using SAS 8.2 software (44).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Preliminary Analyses
Three one-way (group) multivariate analyses of variance (MANOVAs) were conducted to test whether medicated and nonmedicated insomniacs significantly differed on the dependent variables. Theses analyses did not show any significant difference for retrospective measures of stress, for prospective daily stress and presleep arousal measures, and for sleep measures (all F values < 1). Thus, medicated and nonmedicated insomnia participants were collapsed into a single insomnia group for all subsequent analyses.

Demographic and Clinical Variables
Table 1 presents the demographic and clinical characteristics of the sample. Groups were not significantly different on gender, marital status, and occupation. However, these analyses revealed a group effect for age (F(1,65) = 13.60, p < .001), sleep medication use (F(1,65) = 9.07, p < .004), and smoking (F(1,65) = 6.42, p < .014). Good sleepers were significantly younger than insomniacs, were using less sleep medication, and were smoking more. However, exploratory step-down ANCOVAs revealed that sleep medication use and smoking failed to reach significance when age was entered as covariate. Thus, only age was retained as a covariate for all subsequent analyses.


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  		TABLE 1. Demographic and Clinical Characteristics of Participantsa
 
One-way (group) ANCOVAs were conducted on the sleep measures to validate the formation of the groups. These analyses revealed significant group differences on measures of sleep efficiency (F(1,64) = 61.31, p < .001) and sleep quality (F(1,64) = 36.91, p < .001). As expected, good sleepers had higher sleep efficiency and better sleep quality than did insomniacs.

One-way (group) ANCOVAs yielded significant differences on the BDI (F(1,64) = 32.73, p < .001) and the BAI (F(1,64) = 15.94, p < .002) measures. The insomnia group reported more intense symptoms of depression and anxiety than did good sleepers, but average scores remained within the nonclinical range. For instance, the average BDI and BAI scores for the insomnia group were 11.7 (SD = 6.1) and 9.2 (SD = 6.2).

Global and Retrospective Measures of Stress and Coping Skills
Group means and standard deviations for global measures of stress (LES, PSS) and coping skills (CISS) are displayed in Table 2. One-way (group) ANCOVAs revealed a significant group difference for the frequency of major stressful events experienced in the past year (F(1,64) = 6.72, p < .01) and the perceived intensity of negative life events (F(1,64), = 15.67, p < .001). For both measures, good sleepers reported less frequent and intense negative events than did insomniacs. No significant group difference was observed for the perceived intensity of positive events.


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  		TABLE 2. Means and Standard Deviations for Retrospective Global Stress and Coping Measuresa
 
There was a significant group difference on the perception of control over stress (F(1,64) = 8.32, p < .005), with insomniacs reporting a lower level of perceived control than good sleepers. ANCOVAs showed that insomniacs were more likely to endorse the negative items (F(1,64) = 8.46, p < .005) and less likely to endorse the positive items (F(1,64) = 4.17, p < .05). Additional analyses on retrospective measures revealed that insomniacs relied significantly more often on emotion-oriented coping strategies than good sleepers (F(1,64) = 3.90, p < .05). No significant group difference was found for task-oriented coping strategies.

Prospective Daily Self-Monitoring Variables
Table 3 shows group means (each participant score was computed from the mean of 21 days of self-recording) and standard deviations for the variables derived from the DSI and the PSAS. One-way (group) ANCOVAs revealed no significant difference between groups for the frequency of daily minor stressors experienced during this 3-week period. However, there was a significant difference for the sum of ratings (F(1,64) = 4.23, p < .04) and the impact of daily stressors (F(1,64) = 10.54, p < .002), suggesting that insomniacs perceived, on average, the same amount of daily events as more stressful than good sleepers.


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  		TABLE 3. Means and Standard Deviations of Prospective Daily Stress and Presleep Arousal Variablesa
 
There were significant group differences for presleep cognitive (F(1,64) = 19.62, p < .001) and somatic arousal (F(1,64) = 12.75, p < .001) subscales. Insomniac participants reported higher presleep cognitive and somatic arousal states than did good sleepers.

Prospective Time-Series Analyses
All seven prospective daily variables (stress frequency, stress sum, stress impact, presleep cognitive and somatic arousal, sleep efficiency, and sleep quality) were analyzed as within-subject time-series data. Hence, significant autocorrelation (ie, serial dependency), checked from lag 1 to 3, was removed from each measure’s time series for every participant. Data from three participants were excluded (ie, one had only 7 of 21 days of data, and daily arousal data from the other participants showed no variance), leaving a sample of 64 participants for these analyses. Once serial dependency was removed, time-series data were seen as statistically independent, and Pearson correlation coefficients between all seven residual time series were computed for every participant. Using standard meta-analytic procedures (41, 42) , all individual coefficients were transformed into effect-size Zr values using the Fisher Z transformation and were averaged to test the existence of significant relationships between stress, presleep arousal, and sleep. Because daytime stress is presumed to affect subsequent presleep arousal, which in turn affects subsequent sleep, only logical and prospective relationships were examined (stress -> arousal, stress -> sleep, and arousal -> sleep). Thus, the sequential assessment of measures associated with prospective within-subject analysis allowed a naturalistic causal test of the impact of stress and arousal on sleep.

Pearson correlation coefficients between daily stress and sleep measures ranged from -0.06 to -0.10 (all p values < .05), suggesting that for a given day, a higher level of stress was associated with more disturbed sleep the next night. However, the magnitude of these effects was small according to the guidelines of Cohen (45). Relationships between daily stress and presleep arousal were also significant (r values ranged from 0.16 to 0.22), indicating that for a given day, a high level of stress was associated with higher level of cognitive and somatic arousal at bedtime. Correlation coefficients between presleep arousal and sleep measures were moderate according to the guidelines of Cohen (45) (r values ranged from -0.20 to -0.35; all p values < .05), suggesting that for a given day, a higher level of presleep arousal was associated with more disrupted sleep.

A mediational analysis was completed to test whether presleep arousal acted as a mediator of the relationship between daily stress and sleep. Hence, partial Pearson correlations between daily stress and sleep residual time series were computed for every participant, with cognitive and somatic presleep arousal residual time series as covariates. As expected, all significant correlations between daily stress and sleep disappeared, which is a clear demonstration of a mediational effect of presleep arousal (46). Consequently, only the more parsimonious mediational model of the impact of stress on sleep via presleep arousal is displayed in Figure 1.



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  		Fig. 1. Mediational model of the prospective impact of daily stress on sleep via presleep arousal during a 21-day period (N = 64). Data are averaged Pearson correlation coefficients (all p values < .001).

 
A one-way (group) MANOVA failed to reveal significant differences between insomniacs and good sleepers on all prospective relationships (F(10,53) = 1.31, NS), suggesting that the processes governing the impact of daily stress on sleep via presleep arousal are similar for good sleepers and insomniacs.

Path Analysis Model of the Impact of Coping on Stress, Presleep Arousal, and Sleep
Because the coping measure was taken only once, it could not be included in the mediational prospective model. Consequently a transversal path model was built to study the contribution of coping on the process detailed in Figure 1 (ie, stress -> arousal -> sleep). Three multivariate canonical correlations between the four sets of measures (coping, stress, presleep arousal, and sleep) were computed to identify the most informative measure of each set (results not reported here). Only the measures that showed the largest contribution to the canonical variance were included in the path model. Hence, a model based on emotional coping, stress impact, cognitive presleep arousal, and sleep efficiency is displayed in Figure 2.



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  		Fig. 2. Path analysis model of the retrospective relationships between emotion-oriented coping, daily stress impact, cognitive presleep arousal, and sleep efficiency (N = 67). Data are ß coefficients adjusted for age. *p < .05, **p < .001, aNS.

 
Interestingly the path model revealed that emotion-focused coping indirectly influenced sleep efficiency by increasing the stress impact but also to a lesser extent by increasing cognitive presleep arousal. No direct relationship was found between coping and sleep efficiency. The significant relationships found in the lower part of Figure 2 (ie, stress -> arousal -> sleep) were not surprising since they were already revealed by the prospective mediational model.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
ACKNOWLEDGMENTS
 REFERENCES
 
This study examined the role of stress, arousal, and coping skills in primary insomnia. The results showed that the frequency of daily minor stressors was comparable for good and poor sleepers, but the perceived impact of those stressors, as well as the intensity of more major negative life events, was higher for insomniacs than for good sleepers. Individuals with insomnia perceived their lives as more stressful, relied more on emotion-focused coping strategies, and reported higher levels of bedtime arousal than did good sleepers. The relationship between daytime stress and nighttime sleep was mediated by bedtime arousal and, to a lesser extent, by coping skills.

The first finding of interest is that insomniacs and good sleepers do not differ in the frequency with which they experience daily minor stressors; rather it is their appraisal of those events that is different, with poor sleepers evaluating both daily minor events and major life events as more stressful than good sleepers. This result suggests that appraisal processes, rather than the actual stress itself, is implicated in the genesis of sleep disturbances. A related finding is that insomniacs perceived their lives as more stressful with more unpredictable and uncontrollable situations than good sleepers. This result is not surprising given that insomniacs tend to appraise their sleep in a similar fashion, that is, as unpredictable and uncontrollable (5, 47) . Collectively these data are consistent with and extend previous findings on the role of stress on sleep (6–11, 19) . In addition, these data complement previous reports that have characterized the psychological profile of insomniacs as an anxiety-prone, obsessive-worrisome cognitive style (5, 13, 48–50) . Insomniacs might then have a greater predisposition to ruminate about stressors and, perhaps, to amplify their impact on one’s life, all of which would enhance the risk for sleep disturbances.

The second objective of this study was to evaluate prospectively the relationship of daily stress to subsequent bedtime arousal and sleep quality. Significant correlations were obtained among those three sets of variables. Higher stress during the day was associated with higher cognitive and somatic arousal at bedtime, which in turn was associated with poorer sleep efficiency and quality. The strength of the relationship between stress and arousal was again greater for the impact factor than for the frequency of daily stressors. More importantly, the significant relationships between daytime stress and sleep were no longer present when presleep arousal was partialed out, a finding that would clearly suggest that arousal plays a mediating role between stress and sleep. Furthermore, the path analytic findings (Fig. 2) would also implicate coping skills as an additional mediating variable of this relationship between stress and insomnia. Together these findings provide evidence of a clear association between stress and sleep and suggest that this relationship is mediated primarily by presleep arousal and secondarily by appraisal processes.

If this model is valid, individuals who are exposed to daily stressors and appraised them as stressful would be more susceptible to experience an elevated presleep arousal state and subsequent sleep disturbances. This is quite plausible given the finding that poor sleepers tended to rely more frequently than good sleepers on emotion-oriented coping strategies (not intended to resolve the problem but to lessen the emotional distress) when facing stressful situations. This might explain why not everyone exposed to daytime stressors subsequently experience sleep difficulties; for example, a person with poor coping skills might focus on the underlying negative emotion and remain hyperaroused at bedtime, whereas someone with more efficient coping skills might use those skills as a buffer against the same stressor, which would minimize bedtime arousal and sleep disturbances.

The present results need to be interpreted cautiously because of some methodological limitations. First, all data are based on subjective and self-report measures. Despite the importance of measuring the subjective perception of sleep and stress, objective measures of sleep (polysomnography) and stress would be useful to corroborate the present findings. The retrospective nature of several stress measures also raises the possibility that responses to some of those instruments was influenced by memory and selective recall biases. On the CISS for instance, participants were asked about their typical reactions when facing a stressful situation; however, it is possible that appraisal of their behaviors in a specific context was difficult to remember or to judge accurately, or that some respondents were inclined to report using strategies that seemed more socially desirable. Finally, the present results generalize only to primary insomniacs because potential participants with comorbid medical or psychiatric illness were excluded from the study.

Despite these limitations, this study expands on previous investigations (6–8, 11) that have examined the relationship of stress, arousal, and coping to sleep disturbances. Additional research using a longitudinal design would be useful to examine more closely the temporal relationship of minor and major stressors on sleep. Prospective and daily measures of coping strategies actually used in day-to-day situations could also yield a more valid sampling than global and retrospective assessment of those skills. The addition of biological measures of stress and immune functions is also likely to yield a more comprehensive understanding of the relationship of stress, arousal, and insomnia (51, 52) . A better understanding of the role of stress and coping should lead to more specific and effective treatment approaches for the management of insomnia. Meanwhile, the main implication of the present study for the clinical management of insomnia is that treatment should not focus too narrowly on reducing stress and arousal; a more effective approach may be to rely on clinical procedures (eg, cognitive restructuring) specifically aimed at altering appraisal of stress and sleep difficulties and at teaching appropriate coping skills.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
REFERENCES
 
This research was supported in part by the National Institute of Mental Health, Grants 55469 and 60413.

Received for publication February 28, 2001.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 

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