Circadian aspects in the aetiology and pathophysiology of insomnia.

Because the endogenous circadian pacemaker is a very strong determinant of alertness/sleep propensity across the 24 h period, its mistiming may contribute to symptoms of insomnia (e.g., difficulties initiating sleep and maintaining sleep) and to the development of insomnia disorder. Despite the separation of insomnia and circadian rhythm disorders in diagnostic nosology implying independent pathophysiology, there is considerable evidence of co-morbidity and interaction between them. Sleep onset insomnia is associated with later timed circadian rhythms and can be treated with morning bright light to shift rhythms to an earlier timing. It is also possible that the causal link may go in both directions and that having a delayed circadian rhythm can result in enough experiences of delayed sleep onset to lead to some conditioned insomnia or insomnia disorder further exacerbating a delayed circadian rhythm. Early morning awakening insomnia is associated with an advanced circadian phase (early timing) and can be treated with evening bright light resulting in a delay of rhythms and an improved ability to sleep later in the morning and to obtain more sleep. There is some evidence suggesting that sleep maintenance insomnia is associated with a blunted amplitude of circadian rhythm that may be treated with increased regularity of sleep and light exposure timing. However, this is an insomnia phenotype that requires considerably more circadian research as well as further insomnia clinical research with the other insomnia phenotypes incorporating circadian timing measures and treatments.

Associations between chronotypes and psychological vulnerability factors of depression.

Chronotypes have been associated with psychopathology. The eveningness chronotype has been consistently linked with depressed states or depressive disorder, but the underlying mechanism remains unclear. Prior studies have shown associations between chronotype and personality traits that are linked to depression (e.g. neuroticism), but other psychological vulnerability factors have not been previously investigated in relation to chronotypes. The aim of this study was to examine the association between chronotypes, depression and psychological risk factors of depression (namely, cognitive reactivity and worry), in a large cohort of depressed patients and healthy individuals. We used data from the Netherlands Study of Depression and Anxiety (n = 1654), which includes 1227 clinically diagnosed individuals with a lifetime diagnosis of depression and 427 healthy controls. We assessed cognitive reactivity (Leiden Index of Depression Sensitivity-Revised) and trait worry (Penn State Worry Questionnaire). We controlled for sociodemographic factors as well as for insomnia and neuroticism. We found that the evening type is associated with higher cognitive reactivity scores, especially with increased rumination. Cognitive reactivity also mediated the relationship between chronotype and depression status, even when controlling for neuroticism and insomnia. Trait worry was not associated with chronotype. Our findings show that depressogenic cognitions are more prevalent in evening types and perhaps mediate the association between chronotype and depression. Further prospective research is needed to determine the timeline of the association. Nevertheless, results imply that targeting depressogenic cognitive processes, perhaps in combination with chronotherapeutic treatments, may be particularly useful in evening types.

Morningness-eveningness and depressive symptoms: Test on the components level with CES-D in Polish students.

BACKGROUND: The study aimed to elucidate previously observed associations between morningness-eveningness and depressive symptomatology in university students. Relations between components of depressive symptomatology and morningness-eveningness were analysed. METHODS: Nine hundred and seventy-four university students completed Polish versions of the Centre for Epidemiological Studies - Depression scale (CES-D; Polish translation appended to this paper) and the Composite Scale of Morningness. Principal component analysis (PCA) was used to test the structure of depressive symptoms. Pearson and partial correlations (with age and sex controlled), along with regression analyses with morning affect (MA) and circadian preference as predictors, were used. RESULTS: PCA revealed three components of depressive symptoms: depressed/somatic affect, positive affect, interpersonal relations. Greater MA was related to less depressive symptoms in three components. Morning circadian preference was related to less depressive symptoms in depressed/somatic and positive affects and unrelated to interpersonal relations. Both morningness-eveningness components exhibited stronger links with depressed/somatic and positive affects than with interpersonal relations. Three CES-D components exhibited stronger links with MA than with circadian preference. In regression analyses only MA was statistically significant for positive affect and better interpersonal relations, whereas more depressed/somatic affect was predicted by lower MA and morning circadian preference (relationship reversed compared to correlations). LIMITATIONS: Self-report assessment. CONCLUSIONS: There are three groups of depressive symptoms in Polish university students. Associations of MA with depressed/somatic and positive affects are primarily responsible for the observed links between morningness-eveningness and depressive symptoms in university students. People with evening circadian preference whose MA is not lowered have less depressed/somatic affect.

Perceived morningness-eveningness predicts academic adjustment and substance use across university, but social jetlag is not to blame.

Past research has consistently found that evening-types typically report poorer academic adjustment and higher levels of substance use compared to morning-types. An important development within the morningness-eveningness and psychosocial adjustment literature has been the hypothesis that social jetlag (i.e. the asynchrony between an individual's "biological" and "social" clocks) is one factor that may explain why evening-types are at a greater risk for negative psychosocial adjustment. Yet, only a handful of studies have assessed social jetlag. Furthermore, the few studies that have assessed social jetlag have done so only with concurrent data, and thus have not been able to determine the direction of effects among morningness-eveningness, social jetlag and psychosocial adjustment. To address this important gap in the literature, the present 3-year longitudinal study employed the use of a cross-lagged auto-regressive model to specifically examine the predictive role of perceived morningness-eveningness and social jetlag on two important indices of psychosocial adjustment among university students: academic adjustment and substance use. We also assessed whether there would be an indirect effect between perceived morningness-eveningness and psychosocial adjustment through social jetlag. Participants were 942 (71.5% female; M = 19 years, SD = 0.90) undergraduates at a mid-sized university in Southern Ontario, Canada, who completed a survey at three assessments, each one year apart, beginning in first-year university. Measures were demographics (age, gender and parental education), sleep problems, perceived morningness-eveningness, social jetlag, academic adjustment and substance use. As hypothesized, results of path analyses indicated that a greater perceived eveningness preference significantly predicted higher social jetlag, poorer academic adjustment and higher substance use over time. In contrast, we found no support for social jetlag as a predictor of academic adjustment and substance use, indicating that social jetlag did not explain the link between perceived morningness-eveningness and negative psychosocial adjustment. An important finding was the significant predictive effect of higher substance use on social jetlag over time. Results of the present study highlight the importance of employing a longitudinal framework within which to specifically determine the direction of effects among the study variables in order to validate proposed theoretical models that aim to guide our understanding of how perceived morningness-eveningness, social jetlag, academic adjustment and substance use relate to each other.

Influence of chronotype and social zeitgebers on sleep/wake patterns

Inter-individual differences in the phase of the endogenous circadian rhythms have been established. Individuals with early circadian phase are called morning types; those with late circadian phase are evening types. The Horne and Östberg Morningness-Eveningness Questionnaire (MEQ) is the most frequently used to assess individual chronotype. The distribution of MEQ scores is likely to be biased by several fact, ors, such as gender, age, genetic background, latitude, and social habits. The objective of the present study was to determine the effect of different social synchronizers on the sleep/wake cycle of persons with different chronotypes. Volunteers were selected from a total of 1232 UFPR undergraduate students who completed the MEQ. Thirty-two subjects completed the study, including 8 morning types, 8 evening types and 16 intermediate types. Sleep schedules were recorded by actigraphy for 1 week on two occasions: during the school term and during vacation. Sleep onset and offset times, sleep duration, and mid-sleep time for each chronotype group were compared by the Mann-Whitney U-test separately for school term and vacation. School term and vacation data were compared by the Wilcoxon matched-pair test. Morning types showed earlier sleep times and longer sleep duration compared with evening types (23:00 ± 44 and 508.9 ± 50.27 vs 01:08 ± 61.95 and 456.44 ± 59.08, for the weekdays during vacation). During vacation, the subjects showed later sleep times, except for the morning types, who did not exhibit differences for sleep onset times. The results support the idea that social schedules have an impact on the expression of circadian rhythmicity but this impact depends on the individual chronotype.