In a study that involved over 3,000 people aged 65 or older, researchers found that having subclinical hypothyroidism may double a person's risk of congestive heart failure.

Although past studies have shown a link between hyperthyroidism and clinically detectable hyperthyroidism can lead to heart trouble, this new study is the first to make the connection for subclinical hypothyroidism. This particular kind of the disease is detectable only with a blood test, and does not show any outward signs or symptoms.

The results of this study were presented at the annual meeting of the American Thyroid Association.