Hypothyroidism and Depression: A Narrative Review

Abstract

There has been an established relationship between hypothyroidism and depression. Studies have demonstrated that somatostatin and serotonin influence the hypothalamus-pituitary-thyroid axis, which links hypothyroidism to depression. Multiple studies concluded that undiagnosed, untreated, undertreated patients with hypothyroidism are at increased risk of developing depression. Autoimmune thyroiditis is also associated with an increased risk of depression. Elevated thyroid-stimulating hormone (TSH), antithyroglobulin (TgAb), and thyroid peroxidase antibodies (TPOAb) levels have all been linked to depression and an increased risk of suicide. Moreover, hypothyroidism is known to be one of the leading causes of treatment-resistant depression. Treating underlying hypothyroidism with thyroid replacement therapy could significantly improve mood disorders such as depression. Levothyroxine therapy is also used as adjunctive therapy to antidepressants in the management of depression, and it is known to improve the symptoms of depression rapidly when compared to antidepressants alone. This review strengthens the link between hypothyroidism and depression, and it also demonstrates how treating the underlying hypothyroidism in people who have been diagnosed with depression will be very beneficial.

Keywords: depression; depression in hypothyroidism; hypothyroidism; levothyroxine; subclinical hypothryroidism; thyroid peroxidase antibodies; thyroid replacement therapy; treatment-resistant depression.

Figure 1. Hypothalamic-pituitary-thyroid axis

T3: tri-iodothyronine, T4: thyroxine, TRH: thyrotropin releasing hormone, TSH: thyroid stimulating hormone.