Dependent negative life events and sleep quality: An examination of gene–environment interplay

Negative life events, sleep quality, and depression among older adults in Shandong Province, China: A conditional process analysis based on economic income

AIM

Negative life events have been reported as a risk factor for depression. However, the mechanism between negative life events and depression is still unclear. This study aimed to explore the mediating role of sleep quality and the moderating role of economic income in the association between negative life events and depression among older adults aged 60 years and over.

METHODS

A multi-stage stratified sampling method was used to select elderly individuals over 60 years old in Shandong, China, making use of the Household Health Interview Survey (2020). In total, 3868 older adults completed the measures of negative life events, sleep quality, depression, and economic income.

RESULTS

Negative life events positively predicted depression among the elderly (proportion of direct effect, 55.12%), and poor sleep quality could mediate this association (proportion of indirect effect, 44.87%). Economic income played a moderating role in the relationship between negative life events, sleep quality, and depression (the first and second half of the mediating effect, the direct effect of negative life events on depression). Both effects were weaker among the elderly with higher economic incomes.

CONCLUSIONS

Negative life events had positive effects on depression in older adults. Economic income moderated the direct effect of negative life events and the mediating effect (first and second half) of sleep quality on depression. When the elderly experience negative life events, interventions for improving their sleep quality and financial support could effectively prevent depression. Geriatr Gerontol Int 2024; 24: 751-757.

Negative life events and sleep disturbance among adolescents: Intolerance of uncertainty as mediator and moderator

BACKGROUND

While negative life events (NLEs) have been linked to an increased risk of sleep disturbance among adolescents, the mechanisms of this impact still lack further examination. The current study aimed to explore whether intolerance of uncertainty (IU), a dispositional transdiagnostic vulnerability factor for psychopathology, could act as a mediator and/or moderator in the link from NLEs to sleep disturbance.

METHODS

A longitudinal nested subsample of 54,240 Chinese adolescents (aged 9-19) were surveyed at baseline (Timepoint 1) and six months later (Timepoint 2). They completed questionnaires to assess their IU, NLEs, sleep disturbance and sociodemographic characteristics. Mediation and moderation analyses were conducted to test our hypotheses.

RESULTS

Upon adjusting for covariates, IU was found to mediate the relationship between NLEs and residual changes in sleep disturbance over a six-month period, with the mediation effect accounting for 31.8%. Additionally, the moderating role of IU in this relationship was also identified, suggesting that a high level of IU exacerbated the effect of NLEs on sleep disturbance.

CONCLUSIONS

In conclusion, our findings shed light on the dual roles of IU in the link from NLEs to sleep disturbance, holding significant practical implications for preventing and intervening in sleep disturbance among adolescents. To mitigate the risk of sleep disturbance among adolescents experiencing NLEs, timely assessments of IU and tailored interventions to enhance uncertainty tolerance are necessary.

The interaction between polygenic risk and environmental influences: A direct test of the 3P model of insomnia in adolescents

BACKGROUND

Stress is a universal phenomenon and one of the most common precipitants of insomnia. However, not everyone develops insomnia after experiencing a stressful life event. This study aims to test aspects of Spielman's '3P model of insomnia' (during adolescence) by exploring the extent to which: (a) insomnia symptoms are predicted by polygenic scores (PGS); (b) life events predict insomnia symptoms; (c) the interaction between PGS and life events contribute to the prediction of insomnia symptoms; (d) gene-environment interaction effects remain after controlling for sex.

METHODS

The sample comprised 4,629 twins aged 16 from the Twin Early Development Study who reported on their insomnia symptoms and life events. PGS for insomnia were calculated. In order to test the main hypothesis of this study (a significant interaction between PGS and negative life events), we fitted a series of mixed effect regressions.

RESULTS

The best fit was provided by the model including sex, PGS for insomnia, negative life events, and their interactions (AIC = 26,158.7). Our results show that the association between insomnia symptoms and negative life events is stronger for those with a higher genetic risk for insomnia.

CONCLUSIONS

This work sheds light on the complex relationship between genetic and environmental factors implicated for insomnia. This study has tested for the first time the interaction between genetic predisposition (PGS) for insomnia and environmental stressors (negative life events) in adolescents. This work represents a direct test of components of Spielman's 3P model for insomnia which is supported by our results.

Linking genetic foundations of sleep disturbances to personality traits: a study of mid-life twins

Risk of sleep disturbances depends on individuals' personality, and a large body of evidence indicates that individuals prone to neuroticism, impulsivity, and (low) extraversion are more likely to experience them. Origins of these associations are unclear, but common genetic background may play an important role. Participants included 405 twin pairs (mean age of 54 years; 59% female) from the National Survey of Midlife Development in the United States (MIDUS) who reported on their personality traits (broad and specific), as well as sleep disturbances (problems with falling asleep, staying asleep, waking early, and feeling unrested). Uni- and bivariate biometric decompositions evaluated contributions of genetic and environmental factors to associations between personality and poor sleep, as well as unique contributions from individual traits. Neuroticism, extraversion, conscientiousness, and aggressiveness were the strongest phenotypic predictors of poor sleep. Genetic sources of covariance were about twice as large as non-shared environmental sources, and only shared genetic background accounted for links between aggressiveness and poor sleep. Neuroticism and extraversion accounted for most of the genetic overlap between personality and sleep disturbances. The findings shed light on developmental antecedents of ties between personality and poor sleep, suggesting a larger role of common genetic background than idiosyncratic life experiences. The results also suggest that emotion-related traits play the most important role for poor sleep, compared to other personality traits, and may partially account for genetic associations with other traits.

Behaviour genetics and sleep: A narrative review of the last decade of quantitative and molecular genetic research in humans

During the last decade quantitative and molecular genetic research on sleep has increased considerably. New behavioural genetics techniques have marked a new era for sleep research. This paper provides a summary of the most important findings from the last ten years, on the genetic and environmental influences on sleep and sleep disorders and their associations with health-related variables (including anxiety and depression) in humans. In this review we present a brief summary of the main methods in behaviour genetic research (such as twin and genome-wide association studies). We then discuss key research findings on: genetic and environmental influences on normal sleep and sleep disorders, as well as on the association between sleep and health variables (highlighting a substantial role for genes in individual differences in sleep and their associations with other variables). We end by discussing future lines of enquiry and drawing conclusions, including those focused on problems and misconceptions associated with research of this type. In this last decade our knowledge about genetic and environmental influences on sleep and its disorders has expanded. Both, twin and genome-wide association studies show that sleep and sleep disorders are substantially influenced by genetic factors and for the very first time multiple specific genetic variants have been associated with sleep traits and disorders.

Associations between experienced aggression, poor sleep, and suicide risk among Chinese adolescents

STUDY OBJECTIVES

The physical and mental health of adolescents is an important study area. This study aims to examine the occurrence of aggression, sleep disturbances, and suicide risk among Chinese adolescents, along with the relationships between these factors.

METHODS

This is a cross-sectional study conducted through an online survey. Of the original 7011 Chinese adolescent respondents, the analysis included data from 6122 adolescents, aged between 12 and 18 years, from 23 regions, whose average age was 16.12 (±1.44) years, with 48.8% being male. While the chi-square test and t-test were used for analyzing demographic data and continuous variables, respectively, mediation analysis was used to explore the mechanism of experiencing aggression on suicide risk. The respondents' sleep quality, nightmare distress, daytime sleepiness, fatigue, and suicide risk were assessed using the Pittsburgh Sleep Quality Index (PSQI), Nightmare Distress Questionnaire-Chinese version (NDQ-CV), Chinese Adolescent Daytime Sleepiness Scale (CADSS), Multidimensional Fatigue Inventory (MFI-20), and the suicide risk module of the Mini-International Neuropsychiatric Interview (MINI), respectively. Four items were used to assess adolescents' experiences with aggression.

RESULTS

Of the respondents, 42% reported experiencing aggression by others, especially parental physical maltreatment. Furthermore, 26.9% of adolescents in school, and in particular, 31.8% in senior high school experienced insomnia symptoms. Adolescents who reported experiences of aggression had more severe insomnia symptoms, nightmare distress, fatigue, and a higher risk of suicide when compared with those who did not (all ps < 0.001). Insomnia symptoms, nightmare distress, and fatigue all mediated the relationship between aggression and suicide risk, and there was a chain of mediating effects between these factors [for total indirect effect β = 1.1512, 95% CI (0.9671 to 1.3426), direct effect β = 0.4934, 95% CI (0.1978 to 0.7891), and total effect β = 1.6446, 95% CI (1.3479 to 1.9414)].

CONCLUSIONS

Our findings indicate that among adolescents, experiencing aggression is associated with an increased suicide risk. In addition to the direct effect of aggression on suicide risk, insomnia, nightmare distress, and fatigue mediate the relationship between aggression and suicide risk. More attention should be paid to adolescents experiencing aggression, and interventions should be implemented and strengthened.

Components of Stress and Their Associations with Sleep Problems: A Cohort Study of Older Employees

OBJECTIVE

To identify latent components from among 13 work and non-work stressors and to examine whether the accumulation of stress factors within these components was associated with sleep problems.

METHODS

A cohort of older employees (n = 2771 individuals, n = 3921 person-observations) responded to at least two surveys. Principal Component Analysis (PCA) was used to identify latent components. Analysis of variance was used to examine their associations with sleep.

RESULTS

The components were: 'Physical workload and shift work', 'Psychosocial workload', 'Social and environmental non-work adversity' and 'Life event- and health-related non-work adversity'. They were consistently associated with sleep problems, except for 'Physical workload and shift work'. 'Social and environmental non-work adversity' was associated with sleep problems at follow-up.

CONCLUSIONS

Clusters of work- and non-work-related stressors were identified, and their accumulation was associated with sleep problems among older employees.

Associations of negative life events and coping styles with sleep quality among Chinese adolescents: a cross-sectional study

BACKGROUND

Limited published research has examined the relationships of negative life events and coping styles with sleep quality in Chinese junior high school students. We aimed to investigate the prevalence of poor sleep quality and to clarify the role of coping styles between negative life events and sleep quality.

METHODS

A cross-sectional study of 3081 students was conducted in Ganzhou City, Jiangxi Province, Southeastern China. Adolescent Self-Rating Life Events Checklist, Simplified Coping Style Questionnaire, and Pittsburg Sleep Quality Index were applied to assess negative life events, coping styles, and sleep quality, respectively. Descriptive analyses, independent-samples t tests, one-way analyses of variance, Pearson correlation analyses, and structural equation modeling (SEM) were applied to analyze the data.

RESULTS

The prevalence of poor sleep quality was 26.7%. Negative life events (B = 0.038, P < 0.001) and negative coping style (B = 0.049, P < 0.001) demonstrated a positive association with poor sleep quality, while positive coping style indicated a negative association with poor sleep quality (B = -0.029, P < 0.001). Interactions of negative life events and coping styles with sleep quality were not found (all P > 0.05). The association between negative life events and sleep quality was mediated by negative coping styles.

CONCLUSIONS

Our results indicated that poor sleep quality was common in these Chinese adolescents. Negative life events and negative coping style were associated with an increased prevalence of poor sleep quality, while the positive coping style was related to a decreased prevalence of poor sleep quality. A negative coping style mediated the association between negative life events and sleep quality.

Stressful life events and poor sleep quality: a cross-sectional survey in the Chinese governmental employees

Evidence has shown that stressful life events are associated with sleep quality, yet studies on employees are scarce. In the present study, we explored the association between stressful life events and sleep quality in Chinese governmental employees. The cross-sectional data on 10,994 Chinese governmental employees aged 20-60 years were derived from a cohort study on chronic diseases of governmental employees in Hunan Province, China. Logistic regression models were used to calculate the adjusted odds ratio (OR) and the 95% confidence interval (CI). Of the participants, 3517 (32.0%) reported poor sleep quality in the past month. Participants who experienced more than two life events in the past year were associated with 3 times (OR: 3.681, 95%CI:3.287-4.123) greater likelihood of poor sleep quality. Negative life events, but not positive life events, were significantly associated with poor sleep quality. Regarding the types of events, economic-related life events were associated with poor sleep quality only in employees aged 20-35 years. Regarding the specific life events, work stress, job dissatisfaction, pregnancy or wife pregnancy,quality in Chinese governmental employees. discord with spouse's parents, separation from spouse due to work, bad relationship between spouse, unsatisfied sex life, misunderstood, blamed, false accusation or argument, and lifestyle changes were significantly associated with poor sleep quality. When stratified by sex, age and occupational position, the association of specific events and sleep quality were different. The present study showed that cumulative life events, negative life events and several specific events were significantly associated with poor sleep quality on Chinese governmental employees.

Examining Response to Negative Life Events Through Fitness Tracker Data

Negative life events, such as the death of a loved one, are an unavoidable part of life. These events can be overwhelmingly stressful and may lead to the development of mental health disorders. To mitigate these adverse developments, prior literature has utilized measures of psychological responses to negative life events to better understand their effects on mental health. However, psychological changes represent only one aspect of an individual's potential response. We posit measuring additional dimensions of health, such as physical health, may also be beneficial, as physical health itself may be affected by negative life events and measuring its response could provide context to changes in mental health. Therefore, the primary aim of this work was to quantify how an individual's physical health changes in response to negative life events by testing for deviations in their physiological and behavioral state (PB-state). After capturing post-event, PB-state responses, our second aim sought to contextualize changes within known factors of psychological response to negative life events, namely coping strategies. To do so, we utilized a cohort of professionals across the United States monitored for 1 year and who experienced a negative life event while under observation. Garmin Vivosmart-3 devices provided a multidimensional representation of one's PB-state by collecting measures of resting heart rate, physical activity, and sleep. To test for deviations in PB-state following negative life events, One-Class Support Vector Machines were trained on a window of time prior to the event, which established a PB-state baseline. The model then evaluated participant's PB-state on the day of the life event and each day that followed, assigning each day a level of deviance relative to the participant's baseline. Resulting response curves were then examined in association with the use of various coping strategies using Bayesian gamma-hurdle regression models. The results from our objectives suggest that physical determinants of health also deviate in response to negative life events and that these deviations can be mitigated through different coping strategies. Taken together, these observations stress the need to examine physical determinants of health alongside psychological determinants when investigating the effects of negative life events.

Assessing the impacts of ALAN and noise proxies on sleep duration and quality: evidence from a nation-wide survey in Israel

Sleep is a reversible state that sustains physiological and psychological processes in humans. As well established, individual-level factors, such as stress, smoking, drugs, and caffeine intake, reduce sleep duration and quality. However, studies of the effect of environmental risk factors, such as artificial light at night (ALAN) and noise, on sleep have been infrequent. Using records obtained from the 2017 Social Survey of Israel and combined with ALAN satellite data and various proxies for traffic noise, the present study aimed to determine how the combination of ALAN and traffic noise impact sleep duration and quality in urban areas. The increase of road density at the place of residence reduces average sleep duration by ~4.5% (~18 min.) and increases the frequency of reported sleep difficulties by ~3.5%, all other factors held equal. Similarly, an increase in ALAN exposure reduces average sleep duration by ~3% (~12 min) and increases the frequency of reported sleep difficulties by ~11%. The study also reveals a significant interaction between the two environmental risk factors in question, with the adverse impact of ALAN on sleep quality especially pronounced in high noise exposure areas.

Brain mechanisms of insomnia: new perspectives on causes and consequences

While insomnia is the second most common mental disorder, progress in our understanding of underlying neurobiological mechanisms has been limited. The present review addresses the definition and prevalence of insomnia and explores its subjective and objective characteristics across the 24-hour day. Subsequently, the review extensively addresses how the vulnerability to develop insomnia is affected by genetic variants, early life stress, major life events, and brain structure and function. Further supported by the clear mental health risks conveyed by insomnia, the integrated findings suggest that the vulnerability to develop insomnia could rather be found in brain circuits regulating emotion and arousal than in circuits involved in circadian and homeostatic sleep regulation. Finally, a testable model is presented. The model proposes that in people with a vulnerability to develop insomnia, the locus coeruleus is more sensitive to-or receives more input from-the salience network and related circuits, even during rapid eye movement sleep, when it should normally be sound asleep. This vulnerability may ignite a downward spiral of insufficient overnight adaptation to distress, resulting in accumulating hyperarousal, which, in turn, impedes restful sleep and moreover increases the risk of other mental health adversity. Sensitized brain circuits are likely to be subjectively experienced as "sleeping with one eye open". The proposed model opens up the possibility for novel intervention studies and animal studies, thus accelerating the ignition of a neuroscience of insomnia, which is direly needed for better treatment.

Association of job stress, CLOCK gene polymorphism and their interaction with poor sleep quality

Job stress and the Circadian Locomotor Output Cycles Kaput (CLOCK) gene could affect circadian rhythm and sleep quality. The main aim of our present study was to investigate the association of job stress, CLOCK gene polymorphism and their interaction with sleep quality in a non-clinical Chinese Han population, which has not been reported to date. Using a cross-sectional design, 450 subjects were recruited in Beijing. Sleep quality was measured with the Pittsburgh Sleep Quality Index (PSQI) and job stress was measured with the Work Stress Scale. CLOCK gene rs11932595 polymorphism was genotyped in 297 blood samples. Correlation analysis showed a close but different association of high job stress with the PSQI and its components. Analysis of variance showed significant main effects of the CLOCK gene rs11932595 polymorphism. G-allele carriers had a higher score in the PSQI, sleep duration, sleep latency and sleep disturbances. Further interaction analyses showed an ordinal interaction on sleep duration, and a disordinal interaction on daytime dysfunction. Specifically, G-allele carriers had poorer sleep duration than AA homozygotes when in high job stress, while the two subgroups displayed similar sleep duration when in low job stress, conforming to the diathesis-stress model. In comparison to G-allele carriers, AA homozygotes experienced less daytime dysfunction when in low job stress whereas more daytime dysfunction when in high job stress, fitting with the differential susceptibility model. As genetic links have been revealed, our investigation might be conducive for elucidating aetiological factors for sleep quality and targets for implementing interventions to attain good sleep quality.

Does stress influence sleep patterns, food intake, weight gain, abdominal obesity and weight loss interventions and vice versa?

Decades of research have reported only weak associations between the intakes of specific foods or drinks and weight gain and obesity. Randomized controlled dietary intervention trials have only shown very modest effects of changes in nutrient intake and diet composition on body weight in obese subjects. This review summarizes the scientific evidence on the role mental stress (either in or not in association with impaired sleep) may play in poor sleep, enhanced appetite, cravings and decreased motivation for physical activity. All these factors contribute to weight gain and obesity, possibly via decreasing the efficacy of weight loss interventions. We also review evidence for the role that lifestyle and stress management may play in achieving weight loss in stress-vulnerable individuals with overweight.

Relationships between sleep paralysis and sleep quality: current insights

Sleep paralysis is the unusual experience of waking up in the night without the ability to move. Currently little is known about the experience, despite the fact that the vast majority of episodes are associated with extreme fear and in a minority of cases can lead to clinically significant levels of distress. The aim of this work was to review the existing literature pertaining to the relationship sleep paralysis has to sleep more generally, measured both with subjective questionnaires and objective laboratory recordings. In terms of subjective sleep variables, worse sleep quality has been found in multiple studies to be associated with increased odds of sleep paralysis occurrence. In addition, insomnia symptoms (but not a diagnosed insomnia disorder) have also been found to predict sleep paralysis. Associations between sleep paralysis and other unusual and/or threatening sleep experiences such as nightmares, exploding head syndrome, and lucid dreaming have been reported. In terms of objective measurements, the limited literature to date shows sleep paralysis to be a "mixed" state of consciousness, combining elements of rapid eye movement sleep with elements of wakefulness. Future research needs to focus on longitudinal designs to disentangle the direction of effects and more typically employ a broader assessment of sleep paralysis that better captures associated features such as hallucinations, fear, and distress.

Association of sleep disturbance and sexual function in postmenopausal women

OBJECTIVE

Sleep disturbance and sexual dysfunction are common in menopause; however, the nature of their association is unclear. The present study aimed to determine whether sleep characteristics were associated with sexual activity and sexual satisfaction.

METHODS

Sexual function in the last year and sleep characteristics (past 4 wk) were assessed by self-report at baseline for 93,668 women age 50 to 79 years enrolled in the Women's Health Initiative (WHI) Observational Study (OS). Insomnia was measured using the validated WHI Insomnia Rating Scale. Sleep-disordered breathing (SDB) risk was assessed using questions adapted from the Berlin Questionnaire. Using multivariate logistic regression, we examined cross-sectional associations between sleep measures and two indicators of sexual function: partnered sexual activity and sexual satisfaction within the last year.

RESULTS

Fifty-six percent overall reported being somewhat or very satisfied with their current sexual activity, and 52% reported partnered sexual activity within the last year. Insomnia prevalence was 31%. After multivariable adjustment, higher insomnia scores were associated with lower odds of sexual satisfaction (yes/no) (odds ratio [OR] 0.92, 95% CI, 0.87-0.96). Short sleep duration (<7-8 h) was associated with lower odds of partnered sexual activity (yes/no) (≤5 h, OR 0.88, 95% CI, 0.80-0.96) and less sexual satisfaction (≤5 h, OR 0.88, 95% CI, 0.81-0.95).

CONCLUSIONS

Shorter sleep durations and higher insomnia scores were associated with decreased sexual function, even after adjustment for potential confounders, suggesting the importance of sufficient, high-quality sleep for sexual function. Longitudinal investigation of sleep and its impact on sexual function postmenopause will clarify this relationship.

A Longitudinal Twin and Sibling Study of Associations between Insomnia and Depression Symptoms in Young Adults

STUDY OBJECTIVES

To estimate genetic and environmental influences on the associations between insomnia and depression symptoms concurrently and longitudinally.

METHODS

Behavioral genetic analyses were conducted on data from the British longitudinal G1219 twin/sibling study. One thousand five hundred fiftysix twins and siblings participated at Time 1 (mean age = 20.3 years, SD = 1.76). Eight hundred sixty-two participated at Time 2 (mean age = 25.2 years, SD = 1.73 years). Participants completed the Insomnia Symptoms Questionnaire and the Short Mood and Feelings Questionnaire to assess symptoms of insomnia and depression respectively.

RESULTS

Genetic effects accounted for 33% to 41% of the variance of the phenotypes. The phenotypic correlations were moderate (r = 0.34 to r = 0.52). The genetic correlations between the variables were high (0.73-1.00). Genetic effects accounted for a substantial proportion of the associations between variables (50% to 90%). Non-shared environmental effects explained the rest of the variance and covariance of the traits.

CONCLUSIONS

While genetic effects play a modest role in insomnia and depression symptoms separately, they appear to play a more central role in concurrent and longitudinal associations between these phenotypes. This should be acknowledged in theories explaining these common associations.

Do sleep disturbances and psychotic-like experiences in adolescence share genetic and environmental influences?

Sleep disturbances regularly co-occur with clinical psychotic disorders and dimensions of psychotic-like experiences (PLEs). One possible explanation for this, which has yet to be tested, is that similar genetic or environmental influences underlie sleep disturbances and vulnerability to PLEs. We conducted a twin study to test this possibility in relation to sleep disturbances and six specific PLEs in adolescence in the general population. Approximately 5,000 16-year-old twin pairs completed the Pittsburgh Sleep Quality Index and Insomnia Severity Index. PLEs were assessed using the Specific PLEs Questionnaire, comprising five self-report subscales (Paranoia, Hallucinations, Cognitive Disorganization, Grandiosity, and Anhedonia) and one parent-report subscale (Negative Symptoms). The associations between these measures were tested using structural equation twin model fitting. Paranoia, Hallucinations, and Cognitive Disorganization displayed moderate and significant correlations with both sleep measures (0.32-.42), while Negative Symptoms, Anhedonia, and Grandiosity showed lower correlations (0.01-0.17). Genetic and environmental influences significantly overlapped across PLEs (Paranoia, Hallucinations, Cognitive Disorganization) and both types of sleep disturbance (mean genetic and nonshared environmental correlations = 0.54 and 0.24, respectively). These estimates reduced, yet remained significant, after controlling for negative affect. The association between PLEs with sleep disturbances in adolescence is partly due to genetic and environmental influences that are common to them both. These findings indicate that the known neurobiology of sleep disturbance may provide clues regarding the causes of PLEs in adolescence.

Interaction between 5-HTTLPR genotype and cognitive stress vulnerability on sleep quality: effects of sub-chronic tryptophan administration

BACKGROUND

Abundant evidence suggests that allelic variation in the serotonin transporter-linked polymorphic region (5-HTTLPR) influences susceptibility to stress and its affective consequences due to brain serotonergic vulnerability. Based on recent assumptions, the present study examined whether the 5-HTTLPR genotype may also interact with a vulnerability to chronic stress experience (conceptualized by trait neuroticism) in order to influence sleep quality and, additionally, whether this is influenced by brain serotonergic manipulations.

METHODS

In a well-balanced experimental design, homozygous S-allele (n = 57) and L-allele (n = 54) genotypes with high and low chronic stress vulnerability (neuroticism) were first assessed for general past sleep quality during a month before onset of the experiment. Then subjects were assessed for sleep quality following 7 days of tryptophan (3.0g/day) or placebo intake.

RESULTS

Although high neuroticism was significantly related to a higher frequency of stressful life events and daily hassles, it did not interact with the 5-HTTLPR genotype on general past sleep quality. However, as expected, a 7 day period of tryptophan administration was exclusively associated with better sleep quality scores in the S'/S' genotype with high trait neuroticism.

CONCLUSIONS

Current findings suggest that 5-HTTLPR does not directly interact with stress vulnerability in order to influence sleep quality. Instead, based on current and previous findings, it is suggested that the S'/S' 5-HTTLPR genotype promotes the risk for stress-related sleep disturbances because of an increased susceptibility to the depressogenic consequences of stress. Accordingly, by way of reducing depressive symptomatology, tryptophan augmentation may particularly improve sleep quality in stress-vulnerable individuals carrying the 5-HTTLPR S-allele.

Monozygotic twin differences in non-shared environmental factors associated with chronotype

Twin studies have highlighted that a large proportion of variability in chronotype is accounted for by individual-specific environmental factors (non-shared environmental influences). However, little research has aimed to identify specific non-shared environmental influences on chronotype. Although epidemiological studies have shed light on possible environmental influences on chronotype, a substantial amount of research has highlighted the importance of genetic influences on exposure toward specific environments, a process termed gene-environment correlation. It is possible that associations between the environment and chronotype are in part determined by genetics, rather than being purely environmental in origin. One way of exploring the contribution of purely non-shared environmental components on associations between chronotype and the environment is to use the monozygotic twin differences design. This design allows us to tease apart the influences of genetics and the environment to identify purely environmental components. One hundred eighty-nine monozygotic twin pairs (mean age 19.81 years, SD = 1.26, range = 18-22 years, 66.1% female) completed the Horne and Östberg Morningness-Eveningness Questionnaire as a measure of chronotype and questionnaires assessing the following candidate non-shared environmental influences: dependent and independent negative life events, educational attainment, employment status, relationship status, deviant peers, affiliation with deviant peers, general health, smoking, drug use, and alcohol use. Linear regression analyses indicated the presence of gene-environment correlation for the majority of associations between chronotype and candidate environmental influences. When controlling for genetic and shared environmental effects, within monozygotic twin-pair differences in chronotype were associated with within monozygotic twin-pair differences in dependent negative life events (β = -0.27, p < 0.001), educational attainment (β = -0.14, p < 0.05), smoking status (β = 0.22, p < 0.01), and drug use (β = -0.16, p < 0.01). These results suggest that some of the association between these variables is purely environmental in nature. The associations between the remaining environmental variables and chronotype, however, may be intertwined with underlying genetic factors. These findings add to our understanding of genetic and environmental mechanisms underlying the biological clock.

Arizona Twin Project: a focus on early resilience

The Arizona Twin Project is an ongoing longitudinal study designed to elucidate the genetic and environmental influences underlying the development of early competence and resilience to common mental and physical health problems during infancy and childhood. Participants are a sample of 600 twins (25% Hispanic) recruited from birth records in the state of Arizona, United States. Primary caregivers were interviewed on twins' development and early social environments when twins were 12 and 30 months of age. Measures include indices of prenatal and obstetrical risk coded from hospital medical records, as well as primary caregiver-report questionnaires assessing multiple indicators of environmental risk and resilience (e.g., parental warmth and control, family and social support), twins' developmental maturity, temperament, health, behavior problems, and competencies. Preliminary findings highlight the importance of the early environment for infant and toddler health and well-being, both directly and as a moderator of genetic influences. Future directions include a third longitudinal assessment in middle childhood examining daily bidirectional relations between sleep, health behaviors, stress, and mood.

Genetic and environmental influences on sleep quality in middle-aged men: a twin study

Poor sleep quality is a risk factor for a number of cognitive and physiological age-related disorders. Identifying factors underlying sleep quality are important in understanding the etiology of these age-related health disorders. We investigated the extent to which genes and the environment contribute to subjective sleep quality in middle-aged male twins using the classical twin design. We used the Pittsburgh Sleep Quality Index to measure sleep quality in 1218 middle-aged twin men from the Vietnam Era Twin Study of Aging (mean age = 55.4 years; range 51-60; 339 monozygotic twin pairs, 257 dizygotic twin pairs, 26 unpaired twins). The mean PSQI global score was 5.6 [SD = 3.6; range 0-20]. Based on univariate twin models, 34% of variability in the global PSQI score was due to additive genetic effects (heritability) and 66% was attributed to individual-specific environmental factors. Common environment did not contribute to the variability. Similarly, the heritability of poor sleep-a dichotomous measure based on the cut-off of global PSQI>5-was 31%, with no contribution of the common environment. Heritability of six of the seven PSQI component scores (subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, and daytime dysfunction) ranged from 0.15 to 0.31, whereas no genetic influences contributed to the use of sleeping medication. Additive genetic influences contribute to approximately one-third of the variability of global subjective sleep quality. Our results in middle-aged men constitute a first step towards examination of the genetic relationship between sleep and other facets of aging.

The Genesis 12–19 (G1219) Study: A Twin and Sibling Study of Gene–Environment Interplay and Adolescent Development in the UK

The Genesis 12–19 (G1219) Study is an ongoing longitudinal study of a sample of UK twin pairs, non-twin sibling pairs, and their parents. G1219 was initially designed to examine the role of gene–environment interplay in adolescent depression. However, since then data have continued to be collected from both parents and their offspring into young adulthood. This has allowed for longitudinal analyses of depression and has enabled researchers to investigate multiple phenotypes and to ask questions about intermediate mechanisms. The study has primarily focused on emotional development, particularly depression and anxiety, which have been assessed at multiple levels of analysis (symptoms, cognitions, and relevant environmental experiences). G1219 has also included assessment of a broader range of psychological phenotypes ranging from antisocial behaviors and substance use to sleep difficulties, in addition to multiple aspects of the environment. DNA has also been collected. The first wave of data collection began in the year 1999 and the fifth wave of data collection will be complete before the end of 2012. In this article, we describe the sample, data collection, and measures used. We also summarize some of the key findings to date.

Sleep quality and diurnal preference in a sample of young adults: associations with 5HTTLPR, PER3, and CLOCK 3111

Research investigating associations between specific genes and individual differences with regards to the quality and timing of sleep has primarily focussed on serotonin-related and clock genes. However, there are only a few studies of this type and most of those to date have not considered the possibility of gene-environment interaction. Here, we describe associations between sleep quality and diurnal preference and three functional polymorphisms: 5HTTLPR, PERIOD3, and CLOCK 3111. Furthermore, we assessed whether associations between genotypes and sleep phenotypes were moderated by negative life events-a test of gene-environment interaction. DNA from buccal swabs was collected from 947 individuals [mean age = 20.3 years (SD = 1.77), age range = 18-27 years; 61.8% female] and genotyped for the three polymorphisms. Participants completed the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire. There was a significant main effect of 5HTTLPR on sleep quality, indicating that "long-long" homozygotes experienced significantly poorer sleep quality (mean = 6.35, SD = 3.36) than carriers of at least one "short" allele (mean = 5.67, SD = 2.96; β = -0.34, P = 0.005). There were no main effects of 5HTTLPR on diurnal preference; no main effects of PERIOD3 or CLOCK on sleep quality or diurnal preference; and no significant interactions with negative life events. The main effect of the "long" 5HTTLPR allele contradicts previous research, suggesting that perhaps the effects of this gene are heterogeneous in different populations. Failure to replicate previous research in relation to PERIOD3 and CLOCK concurs with previous research suggesting that the effects of these genes are small and may be related to population composition.