Nonshared Environmental Influences on Sleep Quality: A Study of Monozygotic Twin Differences

A narrative review of research linking non-sexual social touch to sleep quality

This narrative review describes the current state of the literature that has examined associations between non-sexual social touch (i.e., affectionate touch, touch therapies, touch with animals and inanimate objects that mimic social touch) and sleep quality. It also highlights areas for future research to clarify the links and to identify underlying mechanisms. Most existing studies have focussed on and shown positive effects of touch therapies (e.g., massage, therapeutic touch) on sleep quality in clinical populations. Although there are fewer studies examining how other forms of social touch are linked with sleep quality, the existing research provides preliminary evidence supporting affectionate touch (e.g., hugging, skin-to-skin contact) and tactile contact with animals (e.g., dogs) and objects that mimic social touch (e.g., robots, weighted blankets) as predictors of better sleep quality, while touch deprivation and touch aversion are associated with worse sleep quality. Informed by the existing literature, we additionally reviewed potential relational-cognitive (e.g., felt-security) and neurobiological (e.g., oxytocin) mechanisms likely to underlie associations between social touch and sleep quality. Overall, current research supports associations between non-sexual social touch and sleep quality. However, future research is needed to establish these links for specific forms of social touch (and in various populations), to test explanatory mechanisms, and to identify boundary conditions. Understanding associations between non-sexual social touch and sleep quality can inform the development of touch-based interventions to improve sleep quality and health.

A narrative review of mechanisms linking romantic relationship experiences to sleep quality

Although a significant body of research has revealed associations between romantic relationship experiences and sleep quality, there has not been clarity regarding the mechanisms underlying such associations. Toward this end, we review the existing studies that have tested mechanisms linking romantic relationship experiences to sleep quality. Guided by both theory and existing research, we organize our review around five key categories of mechanisms that may explain associations between romantic relationship experiences and sleep quality: emotional/affective responses, self-perceptions, social perceptions, self-regulation, and biological functioning. Our review of the literature indicates strong evidence in support of the mediating effects of emotional/affective mechanisms (e.g. emotions and mood states) in explaining associations between various aspects of romantic relationships (e.g. relationship satisfaction, partner conflicts, and attachment orientation) and sleep quality. Although there is ample theoretical support for the other mechanisms proposed, and although all proposed mechanisms have been separately linked to both romantic relationship experiences and sleep quality, few studies have directly tested them, pointing to profitable directions for future research. Understanding underlying mechanisms will enable the development of wise, process-based interventions that target specific mechanisms to improve couple members' sleep quality and romantic relationship functioning.

Cyclical Links Between Daily Partner Interactions and Sleep Quality in Older Adult Couples: The Mediating Role of Perceived Partner Responsiveness and Negative Affect

Researchers have found significant associations between romantic relationship experiences and sleep quality. However, most existing studies are cross-sectional, few have focused on the aging population, and few have considered mechanisms underlying such associations. To address these gaps, 238 older adult couples completed 7-day daily diaries, reporting on their daily relationship, emotional, and sleep experiences. Multilevel structural equation modeling revealed that husbands' higher negative partner interactions and lower positive partner interactions were indirectly associated with their own and their wives' decreased sleep quality that night via lower perceived partner responsiveness and increased negative affect. Moreover, decreased sleep quality was associated with participants' and their partners' increased negative partner interactions and participants' decreased positive partner interactions the next day, with no significant gender differences. This research provides a foundation for future research on cyclical associations between romantic relationship experiences and sleep quality, with implications for relationship-based interventions to improve sleep quality.

Children's objective sleep assessed with wrist-based accelerometers: strong heritability of objective quantity and quality unique from parent-reported sleep

Children's poor sleep is a risk factor for lower cognitive functioning and internalizing and externalizing problems. It is unclear whether genetic and environmental influences vary based on sleep assessment and no studies to date have examined genetic and environmental contributions to links between multiple objective and subjective sleep indicators. Further, nearly all heritability studies rely on subjective parent- or self-report measures of sleep duration and problems. Given these gaps in the literature, we (1) modeled genetic and environmental influences on multiple objective and subjective sleep indicators and (2) estimated genetic and environmental covariances between objective and subjective sleep indicators in middle childhood. Participants were 608 twin children (MZ = 178, same-sex DZ = 234, opposite-sex DZ = 190) assessed at 8 years of age (SD = 0.63 years). Objective nighttime sleep duration, efficiency, sleep onset latency (SOL), midpoint time, and midpoint variability were collected from actigraph watches worn for 7 nights (Mnights = 6.83, SD = 0.62). Children's nighttime sleep duration and daytime sleepiness were assessed via parent report. Findings suggested high additive genetic influence on objective sleep quantity and quality, whereas objective SOL, sleep midpoint time, midpoint variability, parent-reported sleep duration, and daytime sleepiness were largely influenced by the shared environment. Common genetic factors explained associations between objective sleep quantity and quality, but genetics did not account for links with parent-reported sleep duration, midpoint time, or midpoint variability. Thus, objective and parent-reported assessments of children's sleep have unique genetic etiologies and should not be used interchangeably in the sleep literature.

Sleep and social relationships in healthy populations: A systematic review

Over the past decade, research linking sleep and social relationships has burgeoned. Researchers across the globe are trying to understand whether the quality and quantity of our social relationships matter for sleep, and vice versa. We conducted a systematic review of the literature, identifying over 200 relevant articles examining sleep and social relationships in healthy populations. Here, we summarize our findings by reviewing 1) links between sleep and broad social ties across the lifespan, and 2) links between sleep and specific social relationships identified in the literature search, including romantic relationships, family relationships, and work relationships. Taken together, the literature provides evidence that the quality and presence of social relationships, especially our closest relationships, play a role in how we sleep. Likewise, sleep appears to influence our social bonds. However, the majority of work is correlational, limiting conclusions about the directionality of these effects. We conclude by synthesizing the findings, considering the limitations of the present literature, and identifying key future directions for this emerging area of research.

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.

Mechanisms underlying the association between insomnia, anxiety, and depression in adolescence: Implications for behavioral sleep interventions

There is robust evidence of an association between insomnia, anxiety, and depression in adolescence. The aim of this review is to describe and synthesize potential mechanisms underlying this association and explore implications for the design of adolescent behavioral sleep interventions. Specifically, we examine whether insomnia symptoms are a mechanism for the development of internalizing symptoms in adolescence and whether sleep interventions are an effective treatment for both insomnia and internalizing symptoms in adolescence because they target the shared mechanisms underlying these disorders. Research using different methodologies points to the role of sequential, parallel, and interacting mechanisms. In this paper, we review a wide range of relevant biological (i.e., polymorphisms and dysregulation in serotonin, dopamine, and circadian clock genes; alterations in corticolimbic and mesolimbic brain circuits; cortisol reactivity to stress; inflammatory cytokine dysregulation; biased memory consolidation; changes in sleep architecture), psychological (i.e., cognitive inflexibility, interpretational biases, judgment biases, negative attribution styles, worry, rumination, biased attention to threat, dysfunctional beliefs and attitudes about sleep, misperception of sleep deficit), and social mechanisms (i.e., reduced and impaired social interactions, unhelpful parenting behaviors, family stress) and propose an integrative multilevel model of how these phenomena may interact to increase vulnerability to both insomnia and internalizing disorders. Several 'biopsychosocial' mechanisms hold promise as viable treatment targets for adolescent behavioral sleep interventions, which may reduce both insomnia and internalizing symptoms.

An examination of the etiologic overlap between the genetic and environmental influences on insomnia and common psychopathology

BACKGROUND

Insomnia is comorbid with internalizing and externalizing psychiatric disorders. However, the extent to which the etiologic influences on insomnia and common psychopathology overlap is unclear. There are limited genetically informed studies of insomnia and internalizing disorders and few studies of overlap exist with externalizing disorders.

METHODS

We utilized twin data from the Virginia Adult Twin Studies of Psychiatric and Substance Use Disorders (total n = 7,500). Insomnia, internalizing disorders (major depressive disorder [MDD], generalized anxiety disorder [GAD]), and alcohol abuse or dependence (AAD) were assessed at two time points, while antisocial personality disorder (ASPD) was assessed once. Cholesky decompositions were performed in OpenMx and longitudinal measurement models were run on available phenotypes to reduce measurement error.

RESULTS

The latent additive genetic influences on insomnia overlapped significantly (56% for females, 74% for males) with MDD and were shared completely (100%) with GAD. There was significant overlap of latent unique environmental influences, with overlap ranging from 38 to 100% across disorders. In contrast, there was less genetic overlap between insomnia and externalizing disorders, with 18% of insomnia's heritability shared with AAD and 23% with ASPD. Latent unique environmental overlap between insomnia and both externalizing disorders was negligible.

CONCLUSIONS

The evidence for substantial genetic overlap between insomnia and stable aspects of both internalizing disorders suggests that there may be few insomnia-specific genes and investigation into unique environmental factors is important for understanding insomnia development. The modest overlap between insomnia and externalizing disorders indicates that these disorders are genetically related, but largely etiologically distinct.

Gene-Environment Interplay in the Context of Romantic Relationships

A growing body of research supports an important role for genetic factors on intimate, romantic relationships. In this article, we review research that has examined the interplay between genetic and environmental influences on romantic relationships and the associations between relationship outcomes and important individual differences related to relationships. We first elaborate on how behavioral genetic and molecular genetic methods can be used to understand the etiology of relationship outcomes. We then review empirical studies that have examined gene-environment correlations and gene-by-environment interactions in predicting romantic relationship outcomes (e.g., relationship formation, relationship quality and functioning, relationship dissolution) and their association with the physical health, mental health, and well-being of relationship partners.

Risk factors for low back pain: insights from a novel case-control twin study

BACKGROUND CONTEXT

Previous research has failed to identify strong consistent risk factors for low back pain (LBP). A plausible solution is to conduct hypothesis-generating studies, such as twin case-control surveys.

PURPOSE

To investigate twins' perceptions of the factors responsible for within-pair differences in LBP.

STUDY DESIGN

A case-control twin survey.

PATIENT SAMPLE

Twenty-four twin pairs that were generally and broadly discordant for LBP history.

OUTCOME MEASURES

The participants' perceptions of the factors that could explain within-pair differences in LBP history.

METHODS

Twins were asked to identify the factors responsible for within-pair differences in LBP. Closed questioning collected information on the known risk factors and open-ended questioning was used to reveal novel factors. The frequency of risk factors was presented to investigate the individual's perception of the contribution of factors in the development of their own and/or their twin's experience of LBP.

RESULTS

The most frequent factors reported in the closed questioning related to the physical workload of the lumbar spine, specifically, the engagement in different types of work (n=23/24 pairs, 96%). Types of work included those involving heavy loads, lifting, manual tasks, awkward postures, and gardening. Single trauma or injury and vigorous physical activity participation were perceived as the contributors by 79% (n=19/24 pairs) and 88% (n=21/24 pairs) of the pairs, respectively. Open-ended questioning did not reveal new risk factors for LBP.

CONCLUSIONS

Twins attributed the differences in LBP history to risk factors related to physical workload. Future studies investigating the risk factors for LBP should include valid and comprehensive assessments of these factors.

Addressing sleep disturbances: an opportunity to prevent cardiometabolic disease?

There is increasing awareness of the role of sleep disturbance as an important factor in health and disease. Although sub-clinical sleep disturbances (insufficient sleep duration or inadequate sleep quality) may be difficult to assess with conceptual and/or methodological clarity, this review attempts to summarize and synthesize these findings. First, the concept of sleep disturbance in a public health context is introduced, to provide context and rationale. Second, operational definitions of 'cardiometabolic disease' and 'sleep disturbance' are offered, to address many unclear operationalizations. Third, the extant literature is summarized regarding short or long sleep duration and/or insufficient sleep, insomnia and insomnia symptoms, general (non-specific sleep disturbances), circadian rhythm abnormalities that result in sleep disturbances, and, briefly, sleep-disordered breathing. Fourth, the review highlights the social/behavioural context of sleep, including discussions of sleep and race/ethnicity, socio-economic position, and other social/environmental factors, in order to place these findings in a social-environmental context relevant to public health. Fifth, the review highlights the issue of sleep as a domain of health behaviour and addresses issues regarding development of healthy sleep interventions. Finally, a research agenda of future directions is proposed.

Clinical Implications of Impaired Sleep

Despite its pervasiveness in primary care, deficient sleep often is underappreciated as a cue to other health risks. Accordingly, this review discusses contemporary evidence-based perspectives on impaired sleep and its associations with other lifestyle medicine concerns, including obesity, cardiovascular conditions, psychological problems, and health-compromising habits. The potential clinical benefits of promoting sleep health also will be considered.

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.

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.