Temporal relationships between physical symptoms and psychiatric disorder. Results from a national birth cohort

Physical symptoms and psychiatric disorder are associated. We aimed to investigate which comes first.

Data from the Medical Research Council National Survey of Health and Development, a population-based birth cohort study were used at two time points: 36 and 43 years. Six physical symptoms were reported at both time points. The Present State Examination and Psychiatric Symptom Frequency interviews were administered at 36 and 43 years respectively. Odds ratios corrected for a variety of confounders were used to describe the associations between physical symptoms and psychiatric disorder across these two time points.

Psychiatric disorder increased the odds of reporting symptoms 3-7-fold. The relationship strengthened when the outcome was defined as suffering from multiple symptoms. Population attributable risk of psychiatric disorder and subsyndromal disorder in causing multiple somatic symptoms was 40.3%. Prospectively, psychiatric disorder at 36 years was a predictor for five of the six physical symptoms. Three physical symptoms at 36 years predicted new onset of psychiatric symptoms at 43 years.

Psychiatric disorder is strongly related to physical symptoms. The direction of causality may operate in both directions. Assuming a causal relationship, psychiatric disorder (including sub-threshold disorders) could account for at most 40% of cases of multiple physical symptoms.