Hypothyroidism is the most common type of thyroid problem. The incidence tends to increase with age, with women older than 60 at highest risk. Hypothyroidism tends to run in families.

• Hypothyroidism occurs in 4 to 5 out of 100 people in the United States.³
• Hypothyroidism is more common in older people than in younger and more common in women than in men.
• In iodine-deficient areas of the world, 10 to 20 times more people have hypothyroidism than in the United States.¹
• Mild (subclinical) hypothyroidism affects up to 20 out of 100 of women older than 60.³
• About 2 out of 100 of pregnant women in the United States develop hypothyroidism.³
• 1 out of every 4,000 infants born worldwide has hypothyroidism. Girls are twice as likely to have hypothyroidism as boys.²