Mediators of treatment effect in minimal-contact cognitive behaviour therapy for severe health anxiety: A theory-driven analysis based on a randomised controlled trial

Cognitive behaviour therapy (CBT) is efficacious for severe health anxiety, but little is known about mechanisms. We analysed putative mediators of change based on 13 weekly assessments in a randomised controlled trial (N = 132) of exposure-based minimal-contact CBT (guided Internet-delivered CBT, unguided Internet-delivered CBT and bibliotherapy) vs. a waitlist control for severe health anxiety. We hypothesised that the effect of CBT on health anxiety would be mediated by non-reactivity to inner experiences, health anxiety behaviours and perceived competence. We also explored somatosensory amplification. In parallel process growth models, non-reactivity, health anxiety behaviours and perceived competence – but not somatosensory amplification – were influenced by CBT and associated with health anxiety. Random intercepts cross-lagged panel models were used to study within-individual ordering of change. None of the putative mediators systematically predicted subsequent changes in health anxiety. Rather, changes in health anxiety predicted subsequent changes in all putative mediators. In summary, CBT influenced health anxiety behaviours, non-reactivity to inner experiences and perceived competence, and these variables were associated with the outcome. However, their role as mediators was not corroborated because we found no evidence that changes in these variables predicted subsequent changes in health anxiety. We encourage further research into mediators of CBT for health anxiety.