Patients with hyperthyroidism are at increased risk of psychiatric morbidity, according to findings from a new Danish nationwide register study.

“It is well-accepted that thyroid hormones have major effects on developmental and physiological processes of the central nervous system,” explains Frans Brandt (Odense University Hospital, Denmark), the lead author of the study. However, data on the link between thyroid hormones and psychiatric disorders have so far been inconclusive. Brandt and colleagues therefore used data from two Danish nationwide health registers on hospitalization and pharmacological treatment to evaluate the association between hyperthyroidism and psychiatric morbidity.

The registers included 2,631 patients with hyperthyroidism; each patient was matched with four individuals from the registers who did not have hyperthyroidism. The participants were followed up for a mean of 6 years. The researchers then determined the risk of psychiatric morbidity before and after the diagnosis of hyperthyroidism.

Before they had been diagnosed with hyperthyroidism, patients had an increased risk of being hospitalized with a psychiatric diagnosis and were more likely than the control individuals to be taking antipsychotics, antidepressants or anxiolytics. These risks were further increased after patients had been diagnosed as having hyperthyroidism. When patients were stratified according to whether they had autoimmune or nonautoimmune thyroid disease, those with autoimmune thyroid disease had the highest risk of psychiatric morbidity. “These results are supportive of psychiatric disease being attributed to autoimmunity rather than to the hyperthyroid state,” says Brandt.

The researchers note that their study lacks information about what treatment the patients received for hyperthyroidism, the possible effects of these treatments and biochemical data. They are now planning studies to address these gaps. “In particular, we aim to evaluate the biochemical severity and effect of treatment of hyperthyroidism in respect to psychiatric outcome,” concludes Brandt.