Lower TSH and higher T4 levels are associated with current depressive syndrome in young adults

The relationship of individual thyroid function indices to depression in those without a history of prior thyroid dysfunction is uncertain.

We examined the relationship between thyroid-stimulating hormone (TSH) and thyroxine (T4) levels and current or lifetime history of depressive symptoms using information from 6869 participants, aged 17-39 years, in the Third National Health and Nutrition Examination Survey without history of thyroid-related illness.

We found that lower TSH and higher T4 levels were associated with current depressive syndrome in men, but only higher T4 levels correlated with current depressive syndrome in women. Lifetime depressive syndrome was associated with neither TSH level nor T4 levels in men or women.

These findings suggest that transient or 'state dependent' changes are associated with depression in those without a history of thyroid illness. Further studies to discern whether these depression-associated changes represent distinct endophenotypes of depression should be encouraged.