Title: Internalizing and Externalizing Behavior Problems in Childhood and Early Development of Cardiovascular and Diabetes Risk
Description: An accumulating evidence-base indicates that internalizing mental health disorders in adulthood are causally associated with cardiovascular diseases (CVD) and type-2 diabetes (T2DM). It is plausible, however, that the relationship between mental and cardiometabolic ill-health becomes established long before adulthood, and that externalizing problems (the other central domain of common psychopathology) are also involved. These questions, as well as questions on the mechanisms that underlie the relationships, have been insufficiently investigated. The overarching goal of this dissertation was to expand current knowledge on how common mental health problems increase cardiometabolic risk over the life course. First, the prospective association between childhood internalizing (emotional problems) and externalizing problems (hyperactivity and conduct problems) with CVD and T2DM risk in adolescence was assessed in data from the Avon Longitudinal Study of Parents and Children (ALSPAC, N=7,730).

Results showed that hyperactivity problems were associated with insulin resistance (high HOMA-IR); that hyperactivity and conduct problems were each associated with high triglyceride levels; and that emotional problems were inversely associated with high triglyceride levels. These results suggest that childhood externalizing problems are an early life risk factor for CVD and T2DM and that childhood internalizing problems are not a risk factor or, that risk in these children does not become apparent until after adolescence. Second, the mechanisms underlying the prospective association of childhood hyperactivity and conduct problems with high levels of triglycerides in adolescence were investigated using causal mediation methods. Results showed that despite being associated with hyperactivity and with conduct problems, body mass index and lifestyle health behaviors including sleep, diet, physical activity, alcohol, and smoking, together these variables, as measured, mediated only 19.6 % and 19.3% of the associations of hyperactivity and conduct problems with triglycerides, respectively.

These results would suggest that mechanisms other than body adiposity and unhealthy behaviors are also involved and that those mechanisms have a larger role in mediating these relationships. Alternatively, It is possible that the observed small role of health behaviors is due to error in measurement and therefore improving measurements for health behaviors should be a central focus of future work. Third and last, a systematic review of the literature on the relationship between childhood externalizing problems with CVD and T2DM risk was conducted. Studies were graded for propensity to bias. Evidence was summarized and assessed for consistency. Results strongly supported positive associations of externalizing problems with insulin resistance, T2DM, and with increased blood lipids among children and adolescents. Evidence suggested that associations are at least partly independent of body adiposity. Evidence provided mix support for the associations with T2DM and blood lipids in adults and with other outcomes in children or adults.

Studies in children tended to be cross-sectional and to use valid and reliable assessment methods, whereas studies of adults tended to be prospective and to rely on less-valid, less reliable assessment methods. These results warrant more research, specifically prospective studies that track children into young adulthood, that employ well-validated measures of externalizing behaviors, that rely on repeated assessments of T2DM and CVD risk throughout follow-up, and that investigate mechanisms other than body adiposity and health behaviors. Overall, this dissertation has found that childhood externalizing problems are prospectively associated with elevated CVD and T2DM risk, specifically with elevated risk of increased levels of blood lipids and insulin resistance. Unlike studies in adults, this dissertation does not support a role of internalizing problems as risk factors. Among children with externalizing problems, risk becomes evident before adolescence and appears to be largely driven by pathways independent of unhealthy behaviors and body adiposity.

Implications of this research’s findings for health practice were proposed. This dissertation identified several gaps and methodological shortcoming in the extant literature. Recommendations were made for future research, including fundamental next questions to investigate, and study designs and methodologies that are best suited to tackle those questions.