People with hypothyroidism are more likely to develop certain other medical conditions. This may be due to the fact that the symptoms of an underactive thyroid affect so many different areas of the body, including the heart and blood vessels, the skin, the digestive system, and the blood.
For example, there is a likely link between hypothyroidism and sleep apnea. This is thought to be due to an increase in the size of the tongue, which is a possible sign of an underactive thyroid. People with hypothyroidism are also more likely to develop erectile dysfunction, anemia, celiac disease, and high cholesterol, among other things.
(Click Hypothyroidism Symptoms and Signs for a detailed list of indications that a person may have this condition, as well as a discussion on whether symptoms will actually appear.)