Family influences on the association between sleep problems and anxiety in a large sample of pre-school aged twins

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Abstract

Research suggests that environmental influences are important on the association between sleep problems and anxiety in children. This study examines family influences on the association between sleep problems and anxiety in 6000+ twin pairs. Parents provided information on their twins’ anxiety and sleep problems at ages 3 and 4 years. The family influences maternal depression, life events, socio-economic status, family illness, and family disorganization, were examined using parent-report. Family disorganization and maternal depression showed the strongest correlations with sleep problems (r = .20, .21, respectively) and with anxiety (r = .24, .28). Subsequent analyses indicated that family disorganization and maternal depression (examined individually) each accounted for approximately 30% of the association between sleep problems and anxiety (r = .18). The remaining association was mainly explained by environmental factors making children in the same family alike and genetic influences. This study specifies family influences that may be important in the association between sleep problems and anxiety and highlights areas of research that may be worth pursuing in order to further understand the childhood association between sleep problems and anxiety.

Introduction

Sleep problems and anxiety are common in children (Adair and Bauchner, 1993, Kashani and Orvaschel, 1990). These problems can cause distress and are associated with negative outcomes. For example, sleep quality and anxiety have been associated with academic/neurobehavioral performance (Ialongo et al., 1994, Sadeh et al., 2002). Furthermore, these disturbances co-occur in both childhood and adulthood (e.g. Ford and Kamerow, 1989, Garland, 2001). Given the lifelong association between anxiety and sleep problems and the health costs and implications of each and their co-occurrence (e.g. co-occurring problems may incur greater costs than individual problems: Souetre et al., 1994), further research is needed to examine possible origins of this co-occurrence.

Examining twin data provides a means of estimating genetic and environmental influences on associations between traits (Plomin, DeFries, McClearn, & McGuffin, 2001). Two recent genetic studies demonstrated that environmental influences making family members similar to one another (shared environment; C) were important in the association between anxiety and sleep problems in pre-school aged children (Gregory et al., 2004, van den Oord et al., 2000). One study also demonstrated that these environmental factors influencing anxiety were almost identical to those influencing sleep problems (Gregory et al., 2004). In spite of this emphasis on shared environmental factors, genetic factors (A) have also been found to play a significant part in the association between anxiety and sleep problems (Gregory et al., 2004).

Hints as to environmental factors that may increase sibling resemblance for both sleep problems and symptoms of anxiety come from other areas of research. For example, epidemiological studies have linked low socio-economic status (SES) with both anxiety and sleep problems (Miech et al., 1999, Simonds and Parraga, 1982). The organization of the family living environment is another factor linked to a range of childhood problems, including sleep problems (Stores, 1996), although the association between family disorganization and childhood anxiety has not been systematically studied. Life events are also associated with both childhood anxiety and sleep problems (Eley and Stevenson, 2000, Sadeh, 1996). Family illness has been associated with a range of childhood difficulties and is therefore another good candidate for research (Siegel et al., 1992). A specific illness that has received a great deal of research attention is maternal depression. Studies report higher levels of anxiety in children of depressed, compared to nondepressed, mothers (Politano, Stapleton, & Correll, 1992), and maternal depression has been associated with childhood sleep problems (e.g. Lam, Hiscock, & Wake, 2003).

This study examines family environmental influences on the association between anxiety and sleep problems in 6000+ twin pairs aged 3–4 years. Two main hypotheses are addressed. First, certain aspects of the family environment are associated with both anxiety and sleep problems. Second, after controlling for family environmental influences, genetic and environmental factors play a part in the remaining association between sleep problems and anxiety.

Section snippets

Participants

Participants were members of the Twins Early Development Study (TEDS; Trouton, Spinath, & Plomin, 2002). Parents of all twins born in England and Wales during 1994–1996 were contacted by the UK Office of National Statistics and were invited to participate. This study focuses on 1994 and 1995 cohorts. Background information was obtained during the first assessment at 18 months. Further assessments were made at 2, 3, 4 and 7 years. 9442 families (86% of those contacted) provided data at the first

Preliminary analyses

Analyses of variance revealed significant sex and zygosity differences for certain variables. As even small differences reach significance in samples of this size, regression analyses examined the proportion of the variance explained by sex and zygosity on these different variables. The proportions of variance explained by sex and zygosity are small (ranging from R2 = .001 for maternal depression to R2 = .005 for SES) and are not examined further.

Phenotypic correlations

There was a modest correlation between sleep

Discussion

Two main questions were examined in this study. First, maternal depression and family disorganization were associated with both sleep problems and anxiety, and each partly explained the overlap between sleep and anxiety. Second, after controlling for the effects of family disorganization and maternal depression in separate models, genetic, shared and nonshared environmental factors each accounted for a proportion of the association between anxiety and sleep problems.

Given previous literature,

Acknowledgements

The authors thank the participants of the Twins Early Development Study, Kathryn Asbury, Jennifer Lau and Andrew McMillan. TEDS is supported by program grant G9424799 from the UK Medical Research Council. The first author is supported by an ESRC Postdoctoral Research Fellowship.

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