Background
Similarities exist between contemporary explanatory models underlying psychosis development, functional somatic symptoms, and health anxiety. The current study aimed to examine the potential interplay between psychotic experiences (and alternate measures of anomalous self-experiences and aberrant attribution of salience) and functional somatic symptoms on the outcome of health anxiety in youths.

Methods
In a prospective general-population birth cohort, the Copenhagen Child Cohort 2000 (CCC2000), data from two time-points were available for 1122 individuals. We assessed the associations between psychotic experiences and functional somatic symptoms with health anxiety both cross-sectionally at ages 11- and 16-years, and longitudinally from age 11 to 16. Further, we examined if there was an interaction between these two domains on the outcome of health anxiety using the interaction contrast ratio.

Results
Functional somatic symptoms and psychotic experiences were strongly cross-sectionally associated with health anxiety at both ages 11 and 16, even after adjustment for general psychopathology. In the longitudinal analyses, functional somatic symptoms, and psychotic experiences at age 11 were not individually associated with health anxiety at age 16 but having both functional somatic symptoms and psychotic experiences was: odds ratio 3.90, 95%CI 1.7–8.9, with suggestion of evidence for interaction beyond the additive effects. This association was attenuated after adjustment for general psychopathology: odds ratio 2.6, 95 % CI 1.0–6.4.

Conclusion
The strong associations between the domains support the idea of possible overlapping mechanisms underlying psychotic experiences, functional somatic symptoms, and health anxiety.