Elize Koopman Verhoeff

We all sleep a third of our lives, added up to 250,000 hours, a sign that sleep must be important. Sleep problems with young children are fairly common, especially with children with behavioral problems. The aim of the research described in this thesis is to investigate how sleep and behavioral problems in children are related. To assess this, we formulated three sub-goals: (1) to study the predictors of childhood sleep problems; (2) to study bidirectionality in the association between sleep problems and behavioral problems; (3) to study the role of self-medication in sleep problems.

For these questions we used the Generation R cohort from Rotterdam, the Netherlands, a study that follows almost 10,000 growing children to young adulthood. All of these children and their parents reported on sleep problems and behavioral problems through questionnaires. In addition, we have conducted home visits to 1500 children to map the sleep for 9 subsequent days in great detail with special movement watches, these actigraphy watches measure movement that we have used to estimate the sleep of the participants. The results of this thesis are summarized below.

Predictors of child sleep
In chapter 2 we studied the predictors of sleep problems in childhood. First, we focused at a predictor in the child’s environment, unstructured family circumstances. Negative family circumstances are often characterized by a lack of structure within the family. We have shown that family irregularity in early childhood is associated with sleep problems and sleep patterns during childhood. This was in addition to previous studies who reported association with fixed routines for bedtime. Interventions to reduce family irregularity have the potential to improve sleep problems and patterns.

The second predictor we investigated was DNA methylation. Complex behavior such as sleep problems and sleep patterns result from the interaction of genes with the environment. One of the models to investigate this is DNA methylation, DNA methylation regulates gene activity in response to genetic and environmental factors – DNA methylation does this by regulating the degree of ‘accessibility’ of the gene, if the gene is unreachable, is no transcription possible and the gene is ‘off’ –. We found an association between actigraphic sleep duration measured and DNA methylation on chromosome 17, including genes previously associated with sleep problems through