Reduced cardiac autonomic flexibility associated with medically unexplained somatic complaints in the context of internalizing symptoms in a preadolescent population sample. The TRAILS Study

Medically unexplained somatic complaints (MUSC; e.g., headaches, abdominal pain) are common in youths and may lead to increased medical consumption, poorer academic attainment, and future somatic ill-health. Dysfunction of the autonomic nervous system as one of the major physiological stress systems has been suggested as an important mechanism in MUSC, although literature is still inconsistent. Currently, large-sized studies using a dimensional approach regarding MUSC in youths are lacking, as is research into patterns of physiological functioning that discriminate between MUSC and anxiety and depression symptoms. The aim of this study was to investigate the relationship of dimensionally measured MUSC with high frequency (HF) HRV and baroreflex sensitivity (BRS) in a large preadolescent population cohort, taking into account co-occurring internalizing symptoms. Our study suggests reduced autonomic flexibility (i.e., lower HF-HRV and lower BRS) in relation to MUSC, independent of co-occurring internalizing symptoms and other important confounders. We provide additional evidence to an earlier TRAILS study, which reported a negative association between cardiac measures (HRV, BRS) and somatic-depressive symptoms (e.g., lack of appetite, overtiredness, Bosch et al., 2009), both studies tapping into different aspects of MUSC. We recommend to take account of MUSC in anxiety and depression research in relation to cardiac autonomic functioning, as findings may differ according to the magnitude of co-occurring MUSC.