Regular exercise, subjective wellbeing, and internalizing problems in adolescence: causality or genetic pleiotropy?

Psychosocial Outcomes in Autistic Children Before and During the COVID-19 Pandemic

Studies on the impact of the COVID-19 pandemic on autistic children's psychosocial outcomes have shown mixed results. In the current study we aimed to gain a better insight into the effect of the COVID-19 pandemic by comparing psychosocial outcomes collected pre-pandemic with data collected during the pandemic. We used the Strengths and Difficulties Questionnaire (SDQ) to examine change over time in psychosocial outcomes of autistic children from pre-pandemic (T0) to lockdown I (T1) and lockdown II (T2) in the Netherlands. We expected a deterioration in psychosocial outcomes. There were 224 participants in T0 and T1, of which 141 also participated in T2. The results showed a surprising improvement in psychosocial outcomes from T0 to T1. Special education and female gender were associated with increased difficulties over time, while higher age was associated with decreased difficulties. At the subdomain level we found that emotional problems remained stable, while hyperactivity, conduct problems, and peer problems decreased, and prosocial behavior increased. Attending special education predicted increased peer problems over time, while higher age predicted both decreased conduct problems and increased prosocial behavior over time. The COVID-19 pandemic may have temporarily improved the fit between the psychosocial needs and the environment for children with autism in the Netherlands.

The relationship between extracurricular sports participation and subjective well-being in junior high school students: a moderated mediation model

Objective

To investigate the direct effect of extracurricular sports participation on subjective well-being among junior high school students, and the mediating role of emotion regulation and moderating role of physical education (PE) class participation.

Methods

Using data from the Program for International Student Assessment (PISA), we analyzed the extracurricular sports participation, emotion regulation, subjective well-being, and PE class participation of 113,203 junior high school students.

Results

After controlling for country, gender, and health status, extracurricular sports participation significantly predicts subjective well-being. Emotion regulation mediates the relationship between extracurricular sports participation and subjective well-being. Both the direct effect of extracurricular sports participation on subjective well-being and the mediating effect of emotion regulation are moderated by PE class participation. The effect is stronger among students with high PE class participation compared to those with low participation.

Conclusion

There is a moderated mediation effect between extracurricular sports participation and subjective well-being among junior high school students. Emotion regulation mediates this relationship, while PE class participation enhances the impact of emotion regulation on subjective well-being.

Genetic confounding in the association of early motor development with childhood and adolescent exercise behavior

INTRODUCTION

Early motor development has been found to be a predictor of exercise behavior in children and adolescents, but whether this reflects a causal effect or confounding by genetic or shared environmental factors remains to be established.

METHODS

For 20,911 complete twin pairs from the Netherlands Twin Register a motor development score was obtained from maternal reports on the timing of five motor milestones. During a 12-year follow-up, subsamples of the mothers reported on the twins' ability to perform seven gross motor skills ability (N = 17,189 pairs), and weekly minutes of total metabolic equivalents of task (MET) spent on sports and exercise activities at age 7 (N = 3632 pairs), age 10 (N = 3735 pairs), age 12 (N = 7043 pairs), and age 14 (N = 3990 pairs). Multivariate phenotypic and genetic regression analyses were used to establish the predictive strength of the two motor development traits for future exercise behavior, the contribution of genetic and shared environmental factors to the variance in all traits, and the contribution of familial confounding to the phenotypic prediction.

RESULTS

Significant heritability (h2) and shared environmental (c2) effects were found for early motor development in boys and girls (h2 = 43-65%; c2 = 16-48%). For exercise behavior, genetic influences increased with age (boys: h2age7 = 22% to h2age14 = 51%; girls: h2age7 = 3% to h2age14 = 18%) paired to a parallel decrease in the influence of the shared environment (boys: c2age7 = 68% to c2age14 = 19%; girls: c2age7 = 80% to c2age14 = 48%). Early motor development explained 4.3% (p < 0.001) of the variance in future exercise behavior in boys but only 1.9% (p < 0.001) in girls. If the effect in boys was due to a causal effect of motor development on exercise behavior, all of the factors influencing motor development would, through the causal chain, also influence future exercise behavior. Instead, only the genetic parts of the regression of exercise behavior on motor development were significant. Shared and unique environmental parts of the regression were largely non-significant, which is at odds with the causal hypothesis.

CONCLUSION

No support was found for a direct causal effect in the association between rapid early motor development on future exercise behavior. In boys, early motor development appears to be an expression of the same genetic factors that underlie the heritability of childhood and early adolescent exercise behavior.

Shared Genetic Risk in the Association of Screen Time With Psychiatric Problems in Children

Importance

Children's exposure to screen time has been associated with poor mental health outcomes, yet the role of genetic factors remains largely unknown.

Objective

To assess the extent of genetic confounding in the associations between screen time and attention problems or internalizing problems in preadolescent children.

Design, Setting, and Participants

This cohort study analyzed data obtained between 2016 and 2019 from the Adolescent Brain Cognitive Development Study at 21 sites in the US. The sample included children aged 9 to 11 years of genetically assigned European ancestry with self-reported screen time. Data were analyzed between November 2021 and September 2023.

Exposure

Child-reported daily screen time (in hours) was ascertained from questionnaires completed by the children at baseline.

Main Outcomes and Measures

Child psychiatric problems, specifically attention and internalizing problems, were measured with the parent-completed Achenbach Child Behavior Checklist at the 1-year follow-up. Genetic sensitivity analyses model (Gsens) was used, which incorporated polygenic risk scores (PRSs) of both exposure and outcomes as well as either single-nucleotide variant (SNV; formerly single-nucleotide polymorphism)-based heritability or twin-based heritability to estimate genetic confounding.

Results

The 4262 children in the sample included 2269 males (53.2%) with a mean (SD) age of 9.9 (0.6) years. Child screen time was associated with attention problems (β = 0.10 SD; 95% CI, 0.07-0.13 SD) and internalizing problems (β = 0.03 SD; 95% CI, 0.003-0.06 SD). The television time PRS was associated with child screen time (β = 0.18 SD; 95% CI, 0.14-0.23 SD), the attention-deficit/hyperactivity disorder PRS was associated with attention problems (β = 0.13 SD; 95% CI, 0.10-0.16 SD), and the depression PRS was associated with internalizing problems (β = 0.10 SD; 95% CI, 0.07-0.13 SD). These PRSs were associated with cross-traits, suggesting genetic confounding. Estimates using PRSs and SNV-based heritability showed that genetic confounding accounted for most of the association between child screen time and attention problems and for 42.7% of the association between child screen time and internalizing problems. When PRSs and twin-based heritability estimates were used, genetic confounding fully explained both associations.

Conclusions and Relevance

Results of this study suggest that genetic confounding may explain a substantial part of the associations between child screen time and psychiatric problems. Genetic confounding should be considered in sociobehavioral studies of modifiable factors for youth mental health.

Social Media Use, Physical Activity, and Internalizing Symptoms in Adolescence: Cross-sectional Analysis

BACKGROUND

Most American adolescents have access to smartphones, and recent estimates suggest that they spend considerable time on social media compared with other physical and leisure activities. A large body of literature has established that social media use is related to poor mental health, but the complicated relationship between social media and symptoms of depression and anxiety in adolescents is yet to be fully understood.

OBJECTIVE

We aim to investigate the relationship between social media use and depression and anxiety symptoms in adolescents by exploring physical activity as a mediator.

METHODS

A Qualtrics survey manager recruited adult panel participants between February and March 2019, who indicated that they had adolescent children who spoke English. A total of 4592 adolescent-parent dyads completed the survey that took approximately 39 minutes. The survey entailed completing web-based questionnaires assessing various aspects of social media use, psychological symptoms, and psychosocial factors. The average age of the adolescent participants was 14.62 (SD 1.68; range 12-17) years, and the majority of the adolescent sample was male (2392/4592, 52.09%).

RESULTS

Total social media use was associated with more depressive symptoms (multiple R²=0.12; F_3,4480=207.1; P<.001), anxiety (multiple R²=0.09; F_3,4477=145.6; P<.001), and loneliness (multiple R²=0.06; F_3,4512=98.06; P<.001), controlling for age and gender. Physical activity was associated with decreased depression and anxiety symptoms after controlling for other extracurricular activities and social media use (multiple R²=0.24; F_5,4290=266.0; P<.001). There were significant differences in symptoms based on gender: female adolescents reported higher rates of social media use and males reported higher rates of depression. Nonbinary and transgender adolescents had higher rates of depression, anxiety, and loneliness than the female and male adolescents in the sample.

CONCLUSIONS

In a nationally representative sample of adolescents, more social media use was associated with more severe symptoms of depression, anxiety, and loneliness. Increased physical activity was associated with decreased depression and anxiety symptoms. Physical activity partially mediated the relationship between social media use and depression and anxiety. As this was a cross-sectional study, we cannot conclude that social media use causes internalizing symptoms or that physical activity leads to decreased internalizing symptoms-there may be additional confounding variables producing the relationships we observed. Physical activity may protect against the potentially harmful effect of social media on some adolescents. The effect sizes were small to medium, and the results should be interpreted with caution. Other limitations of this study include our reliance on self-reporting. Future work should examine social media use beyond how much time adolescents spend using social media and instead focus on the nature of social media activity.

Effects of the aerobic and Pilates exercises on mental health in inactive older women

This study aimed to compare the effect of the Aerobic and Pilates exercises on mental health in inactive older women. Seventy-five inactive aged women were randomly divided into three groups (n = 25); aerobic (62.48 ± 2.87 years), Pilates (62.66 ± 1.68 years), and control group (63.80 ± 3.35 years). The Goldberg General Health Questionnaire assessed mental health. The exercise program was performed for 12 weeks. The results indicate that Pilates exercises are more valuable than aerobic training in depression (p ≤ .05). However, in other mental health components, the difference between the two exercise groups was not statistically significant. According to our results, physical activity, particularly Pilates and aerobic exercises, improves physical health and has a close correlation with the mental health of inactive older women. These results highlight the role of these physical exercise training in older women.

Association between symptoms of sleep apnea and problem behaviors in young adult twins and siblings

BACKGROUND

Sleep apnea is one of the most common sleep disorders and it is related to multiple negative health consequences. Previous studies have shown that sleep apnea is influenced by genetic factors. However, studies have not investigated the genetic and environmental influences of symptoms of sleep apnea in young adults. Furthermore, the underpinnings of the relationship between apnea symptoms and internalizing/externalizing problems are unknown. The objectives of this study were to estimate the magnitude of: (1) genetic and environmental influences on self-reported apnea symptoms; (2) the relationship between self-reported apnea symptoms and internalizing/externalizing traits; (3) genetic and environmental influences on the associations between self-reported apnea symptoms, internalizing behaviors and externalizing behaviors.

METHODS

In a twin/sibling study, univariate and multivariate models were fitted to estimate both individual variance and sources of covariance between symptoms of sleep apnea and internalizing/externalizing behaviors.

RESULTS

Our results show that genetic influences account for 40% of the variance in sleep apnea symptoms. Moreover, there are modest associations between depression, anxiety and externalizing behaviors with apnea symptoms (ranging from r = 0.22-0.29). However, the origins of these associations differ. For example, whereas most of the covariation between symptoms of depression and sleep apnea can be explained by genes (95%), there was a larger role for the environment (53%) in the association between symptoms of anxiety and sleep apnea.

CONCLUSIONS

Genetic factors explain a significant proportion of variance in symptoms of apnea and most of the covariance with depression.

Genetic evidence for a large overlap and potential bidirectional causal effects between resilience and well-being

Resilience and well-being are strongly related. People with higher levels of well-being are more resilient after stressful life events or trauma and vice versa. Less is known about the underlying sources of overlap and causality between the constructs. In a sample of 11.304 twins and 2.572 siblings from the Netherlands Twin Register, we investigated the overlap and possible direction of causation between resilience (i.e. the absence of psychiatric symptoms despite negative life events) and well-being (i.e. satisfaction with life) using polygenic score (PGS) prediction, twin-sibling modelling, and the Mendelian Randomization Direction of Causality (MR-DoC) model. Longitudinal twin-sibling models showed significant phenotypic correlations between resilience and well-being (.41/.51 at time 1 and 2). Well-being PGS were predictive for both well-being and resilience, indicating that genetic factors influencing well-being also predict resilience. Twin-sibling modeling confirmed this genetic correlation (0.71) and showed a strong environmental correlation (0.93). In line with causality, both genetic (51%) and environmental (49%) factors contributed significantly to the covariance between resilience and well-being. Furthermore, the results of within-subject and MZ twin differences analyses were in line with bidirectional causality. Additionally, we used the MR-DoC model combining both molecular and twin data to test causality, while correcting for pleiotropy. We confirmed the causal effect from well-being to resilience, with the direct effect of well-being explaining 11% (T1) and 20% (T2) of the variance in resilience. Data limitations prevented us to test the directional effect from resilience to well-being with the MR-DoC model. To conclude, we showed a strong relation between well-being and resilience. A first attempt to quantify the direction of this relationship points towards a bidirectional causal effect. If replicated, the potential mutual effects can have implications for interventions to lower psychopathology vulnerability, as resilience and well-being are both negatively related to psychopathology.

Becoming active: more to exercise than weight loss for indigenous men

Objective: To understand what motivates sedentary indigenous and ethnic minority men to become more physically active. Design: We use thematic analysis to present data from a qualitative study exploring 23 sedentary indigenous Māori (New Zealand) men's experiences of completing a 12-week exercise intervention to improve their metabolic health. Results: Four themes emerged: The Bros - having fellowship and mutual motivation; Being better informed about exercise; Impacting overall wellbeing; and Disseminating the findings beyond the study Exercise interventions informed by indigenous Māori cultural values and knowledge increased its relevance to their daily lives. The motivation for these indigenous men was more culturally-based external factors than an inherent desire to lose weight. Conclusion: Indigenous and minority men in many developed countries have high morbidity and premature mortality related to sedentary lifestyles. The low uptake of physical activities possibly relates to focusing more on outcomes such as weight loss which lacks cultural relevance. When offering health promotion interventions for marginalized populations these findings highlight the importance of culturally tailoring interventions to the unique sources of motivation for each group to increase activity to improve their efficacy.

Physical activity and subjective well-being in healthy individuals: a meta-analytic review

Longstanding research suggests a positive relation between physical activity and health. However, when investigating this relation most studies focused on the absence of disease or infirmity as health indicators. The relation between physical activity and positive health-related constructs such as subjective well-being (SWB) remains oftentimes unexplored. The present meta-analysis offers a rigorous test of the relation between physical activity and SWB in healthy individuals, by including all different kinds of physical activity and SWB facets from childhood to old age. Random-effects meta-analysis using robust variance estimation revealed a positive relation (d = 0.360, 95% CI [0.301, 0.420]). Our results demonstrate a small beneficial main effect of physical activity on SWB, independent of the prior fitness level of the participants and various characteristics of the physical activity intervention. This effect was found in experimental studies as well as in correlational and quasi-experimental studies. Physical activity was more strongly related to positive affect compared to cognitive well-being and was unrelated to negative affect. Our results provide evidence for the importance of physical activity in the context of well-being. Further, we also systematically review and discuss the large heterogeneity of studies published on this relation and warrant further research regarding underlying mechanisms.

Investigating the association between family connectedness and self-control in adolescence in a genetically sensitive design

Family connectedness is key for the development of self-control in early and middle childhood. But is family connectedness still important during the transitional phase of adolescence, when adolescents demand more independence from their parents and rely more on their peers? The aim of the present study was to investigate the association between family connectedness and self-control, and whether it still holds in adolescence using a genetically sensitive design. Data were used from a large sample of twins aged 14 (N = 11,260) and aged 16 (N = 8175), all enrolled in the Netherlands Twin Register. We applied bivariate twin models and monozygotic twin difference models to investigate the association between family connectedness and self-control and to unravel to what extent genetic and environmental factors explain this association. The results showed that more family connectedness is significantly related to better self-control in adolescence, albeit with a small effect size. Twin analyses revealed that this association was mainly explained by common genetic factors and that the effects of environmental factors were small. The current findings confirm the role of family connectedness in adolescent self-control. Importantly, however, the results demonstrate that phenomena we see within families seem the product of parent and children sharing the same genes rather than being exclusively attributable to environmental processes.

Childhood aggression and the co-occurrence of behavioural and emotional problems: results across ages 3-16 years from multiple raters in six cohorts in the EU-ACTION project

Childhood aggression and its resulting consequences inflict a huge burden on affected children, their relatives, teachers, peers and society as a whole. Aggression during childhood rarely occurs in isolation and is correlated with other symptoms of childhood psychopathology. In this paper, we aim to describe and improve the understanding of the co-occurrence of aggression with other forms of childhood psychopathology. We focus on the co-occurrence of aggression and other childhood behavioural and emotional problems, including other externalising problems, attention problems and anxiety-depression. The data were brought together within the EU-ACTION (Aggression in Children: unravelling gene-environment interplay to inform Treatment and InterventiON strategies) project. We analysed the co-occurrence of aggression and other childhood behavioural and emotional problems as a function of the child's age (ages 3 through 16 years), gender, the person rating the behaviour (father, mother or self) and assessment instrument. The data came from six large population-based European cohort studies from the Netherlands (2x), the UK, Finland and Sweden (2x). Multiple assessment instruments, including the Child Behaviour Checklist (CBCL), the Strengths and Difficulties Questionnaire (SDQ) and Multidimensional Peer Nomination Inventory (MPNI), were used. There was a good representation of boys and girls in each age category, with data for 30,523 3- to 4-year-olds (49.5% boys), 20,958 5- to 6-year-olds (49.6% boys), 18,291 7- to 8-year-olds (49.0% boys), 27,218 9- to 10-year-olds (49.4% boys), 18,543 12- to 13-year-olds (48.9% boys) and 10,088 15- to 16-year-olds (46.6% boys). We replicated the well-established gender differences in average aggression scores at most ages for parental ratings. The gender differences decreased with age and were not present for self-reports. Aggression co-occurred with the majority of other behavioural and social problems, from both externalising and internalising domains. At each age, the co-occurrence was particularly prevalent for aggression and oppositional and ADHD-related problems, with correlations of around 0.5 in general. Aggression also showed substantial associations with anxiety-depression and other internalizing symptoms (correlations around 0.4). Co-occurrence for self-reported problems was somewhat higher than for parental reports, but we found neither rater differences, nor differences across assessment instruments in co-occurrence patterns. There were large similarities in co-occurrence patterns across the different European countries. Finally, co-occurrence was generally stable across age and sex, and if any change was observed, it indicated stronger correlations when children grew older. We present an online tool to visualise these associations as a function of rater, gender, instrument and cohort. In addition, we present a description of the full EU-ACTION projects, its first results and the future perspectives.

Special interests and subjective wellbeing in autistic adults

Special interests form part of the core features of autism. However, to date there has been limited research focusing on the role of special interests in the lives of autistic adults. This study surveyed autistic adults on their special interest topics, intensity, and motivation. It also assessed the relationship between special interests and a range of quality of life measures including subjective wellbeing and domain specific life satisfaction. About two thirds of the sample reported having a special interest, with relatively more males reporting a special interest than females. Special interest topics included computers, autism, music, nature and gardening. Most autistic adults engaged in more than one special interest, highlighting that these interests may not be as narrow as previously described. There were no differences in subjective wellbeing between autistic adults with and without special interests. However, for autistic adults who did have special interests, motivation for engaging in special interests was associated with increased subjective wellbeing. This indicates that motivation may play an important role in our understanding of special interests in autism. Special interests had a positive impact on autistic adults and were associated with higher subjective wellbeing and satisfaction across specific life domains including social contact and leisure. However, a very high intensity of engagement with special interests was negatively related to wellbeing. Combined, these findings have important implications for the role of special interests in the lives of autistic adults. Autism Res 2018, 11: 766-775. © 2018 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Autistic adults reported having special interests in a range of topics, including computers, music, autism, nature and gardening. Special interests were associated with a number of positive outcomes for autistic adults. They were also related to subjective wellbeing and satisfaction across specific life domains including social contact and leisure. Very high intensity of engagement with special interests was related to lower levels of wellbeing. This highlights the important role that special interests play in the lives of autistic adults.

Depression and cardiovascular disease: Epidemiological evidence on their linking mechanisms

Depression's burden of disease goes beyond functioning and quality of life and extends to somatic health. Results from longitudinal cohort studies converge in illustrating that major depressive disorder (MDD) subsequently increases the risk of cardiovascular morbidity and mortality with about 80%. The impact of MDD on cardiovascular health may be partly explained by mediating mechanisms such as unhealthy lifestyle (smoking, excessive alcohol use, physical inactivity, unhealthy diet, therapy non-compliance) and unfavorable pathophysiological disturbances (autonomic, HPA-axis, metabolic and immuno-inflammatory dysregulations). A summary of the literature findings as well as relevant results from the large-scale Netherlands Study of Depression and Anxiety (N=2981) are presented. Persons with MDD have significantly worse lifestyles as well as more pathophysiological disturbances as compared to healthy controls. Some of these differences seem to be specific for (typical versus 'atypical', or antidepressant treated versus drug-naive) subgroups of MDD patients. Alternative explanations are also present, namely undetected confounding, iatrogenic effects or 'third factors' such as genetics.

Genome-Wide Estimates of Heritability for Social Demographic Outcomes

An increasing number of studies that are widely used in the demographic research community have collected genome-wide data from their respondents. It is therefore important that demographers have a proper understanding of some of the methodological tools needed to analyze such data. This article details the underlying methodology behind one of the most common techniques for analyzing genome-wide data, genome-wide complex trait analysis (GCTA). GCTA models provide heritability estimates for health, health behaviors, or indicators of attainment using data from unrelated persons. Our goal was to describe this model, highlight the utility of the model for biodemographic research, and demonstrate the performance of this approach under modifications to the underlying assumptions. The first set of modifications involved changing the nature of the genetic data used to compute genetic similarities between individuals (the genetic relationship matrix). We then explored the sensitivity of the model to heteroscedastic errors. In general, GCTA estimates are found to be robust to the modifications proposed here, but we also highlight potential limitations of GCTA estimates.

Regular exercise behaviour in youth is not related to current body mass index or body mass index at 7-year follow-up

Objective

This population‐based study aimed (1) to test the presence of an association between regular voluntary exercise behaviour (EB) that is performed in leisure time and body mass index (BMI) in youth and (2) to investigate the causal nature of this association using a longitudinal design in genetically informative subjects.

Design and methods

Both EB and BMI were assessed repeatedly over time in 21 458 twin individuals from the Netherlands Twin Register (47.5% male) – first by parental report (ages 7, 10 and 12) and subsequently through self‐report surveys (ages 14, 16 and 18). EB was quantified as weekly metabolic equivalent of task hours.

Results

Correlations over time were higher for BMI than for EB (r ≈ 0.70 vs. r ≈ 0.35) across 12 different follow‐up periods. Cross‐sectionally, regular involvement in EB was not associated with lower BMI in childhood and in genetically identical twin pairs discordant for EB; the exercising twin did not have a lower BMI than the non‐exercising twin. Longitudinally, linear and quadratic relationships between EB and BMI were non‐significant. Changes in EB over time did not induce opposite changes in BMI.

Conclusions

No consistent association between regular EB and BMI was observed from ages 7 to 18 years.

Genetics of wellbeing and its components satisfaction with life, happiness, and quality of life: a review and meta-analysis of heritability studies

Wellbeing is a major topic of research across several disciplines, reflecting the increasing recognition of its strong value across major domains in life. Previous twin-family studies have revealed that individual differences in wellbeing are accounted for by both genetic as well as environmental factors. A systematic literature search identified 30 twin-family studies on wellbeing or a related measure such as satisfaction with life or happiness. Review of these studies showed considerable variation in heritability estimates (ranging from 0 to 64 %), which makes it difficult to draw firm conclusions regarding the genetic influences on wellbeing. For overall wellbeing twelve heritability estimates, from 10 independent studies, were meta-analyzed by computing a sample size weighted average heritability. Ten heritability estimates, derived from 9 independent samples, were used for the meta-analysis of satisfaction with life. The weighted average heritability of wellbeing, based on a sample size of 55,974 individuals, was 36 % (34–38), while the weighted average heritability for satisfaction with life was 32 % (29–35) (n = 47,750). With this result a more robust estimate of the relative influence of genetic effects on wellbeing is provided.

Association between internalizing disorders and day-to-day activities of low energetic expenditure

The objective of this study is to compare energetic expenditure in day-to-day activities among subjects with internalizing disorders (depression and anxiety), externalizing disorders (attention deficit/hyperactivity disorder and oppositional defiant disorder) and healthy children and adolescents without any psychiatric diagnosis. One hundred and five (n = 105) students from a community sample were evaluated throughout a structured psychiatric interview and categorized into three groups: internalizing (n = 54), externalizing (n = 12) and typically developing controls (TDC, n = 39). Energetic expenditure was evaluated using 3-day physical activity record. Subjects with internalizing disorders performed activities with lower energetic expenditure as compared to those with externalizing disorders and TDC. Participants with externalizing disorders had more energetic expenditure variability. Our study suggests that internalizing disorders are associated with activities of low energetic expenditure in day-to-day activities, extending previous findings with physical exercise. These findings may further contribute to the understanding of the associated morbidity previously described in patients with internalizing disorders.

A twin-sibling study on the relationship between exercise attitudes and exercise behavior

Social cognitive models of health behavior propose that individual differences in leisure time exercise behavior are influenced by the attitudes towards exercise. At the same time, large scale twin-family studies show a significant influence of genetic factors on regular exercise behavior. This twin-sibling study aimed to unite these findings by demonstrating that exercise attitudes can be heritable themselves. Secondly, the genetic and environmental cross-trait correlations and the monozygotic (MZ) twin intrapair differences model were used to test whether the association between exercise attitudes and exercise behavior can be causal. Survey data were obtained from 5,095 twins and siblings (18-50 years). A genetic contribution was found for exercise behavior (50 % in males, 43 % in females) and for the six exercise attitude components derived from principal component analysis: perceived benefits (21, 27 %), lack of skills, support and/or resources (45, 48 %), time constraints (25, 30 %), lack of energy (34, 44 %), lack of enjoyment (47, 44 %), and embarrassment (42, 49 %). These components were predictive of leisure time exercise behavior (R(2) = 28 %). Bivariate modeling further showed that all the genetic (0.36 < |rA| < 0.80) and all but two unique environmental (0.00 < |rE| < 0.27) correlations between exercise attitudes and exercise behavior were significantly different from zero, which is a necessary condition for the existence of a causal effect driving the association. The correlations between the MZ twins' difference scores were in line with this finding. It is concluded that exercise attitudes and exercise behavior are heritable, that attitudes and behavior are partly correlated through pleiotropic genetic effects, but that the data are compatible with a causal association between exercise attitudes and behavior.