Mood Disorders Related to Hypothyroidism
Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone. Common causes of hypothyroidism include iodine deficiency, a deficiency of thyroid-stimulating hormone, and an autoimmune disease called Hashimoto’s thyroiditis, which causes destruction of thyroid cells. Hypothyroidism can also be caused by certain types of mood-stabilizing medications, in particular lithium-based drugs used to treat bipolar disorder.
A person with an underactive thyroid gland is likely to have symptoms such as excess weight gain, muscle cramps, joint pain, fatigue, constipation, brittle hair and fingernails, dry skin, cold sensitivity, and low heart rate.
Mood disorders such as depression, mood swings, and irritability are also strongly associated with hypothyroidism, as are sleep disturbances.
People with mood disorders often have a condition called subclinical hypothyroidism, in which thyroid hormone levels appear normal in blood test results, but are in fact abnormal. This subclinical hypothyroidism, which is thought to be the result of autoimmune disease, has been shown to be a significant risk factor for depression.
In addition, people with bipolar disorder are more likely to have subclinical hypothyroidism than people with so-called unipolar depression. People with bipolar disorder who rapidly cycle between mood states are highly likely to have hypothyroidism. This is the case even in people whose hypothyroidism is not caused by the mood-stabilizing medications they are taking.