Subclinical hypothyroidism: a modifiable risk factor for depression?

The authors assessed the lifetime history of major depression in 16 subjects with subclinical hypothyroidism and 15 subjects whose thyroid function was completely normal. The lifetime frequency of depression was significantly higher in the subjects who met the criteria for subclinical hypothyroidism (56%) than in those who did not (20%), suggesting that subclinical hypothyroidism may lower the threshold for the occurrence of depression.