Low Thyroid Increases Heart Risk

Hypothyroidism Relationship to Heart Disease and Cardiac Problems

February 2000 -- "Older women with subclinical hypothyroidism were almost twice as likely as women without this condition to have blockages in the aorta. They were also twice as likely to have had heart attacks."

According to research published in the Annals of Internal Medicine, a slightly underactive thyroid -- the condition known as subclinical hypothyroidism -- is a major heart disease risk for older women. In the Dutch study, which is being called "The Rotterdam Study," it was found that older women with subclinical hypothyroidism were almost twice as likely as women without this condition to have blockages in the aorta. They were also twice as likely to have had heart attacks.

This common condition, which frequently has no obvious symptoms for patients, and no observable symptoms for doctors, is a strong risk factor for both hardening of the arteries and heart attacks in older women.

Subclinical hypothyroidism is detectable by a blood test, known as the Thyroid Stimulating Hormone (TSH) test. For the purposes of this study, subclinical hypothyroidism was defined as a TSH level greater than 4.0 mU/L in the presence of a normal free thyroxine (Free T4) level. Clinical hypothyroidism was defined as a TSH level greater than 4.0 mU/L and a decreased free thyroxine level.

The Rotterdam Study's finding is a strong indication that screening programs to evaluate even slight hypothyroidism in older women could help prevent cardiovascular illness.

The thyroid is a butterfly-shaped gland that wraps around the windpipe, behind the "Adam's Apple" area of the neck. The hormones produced by the gland are essential to stimulating metabolism, growth, and the body's capacity to process calories. An underactive thyroid -- hypothyroidism -- is estimated to affect as many as 10 to 20 percent of women in their lifetimes, and is more common in women than men. The symptoms of hypothyroidism include fatigue, depression, weight gain, hair loss, muscle and joint pains, and many other chronic and debilitating symptoms. Low thyroid can also be linked to increased levels of LDL -- "bad" cholesterol -- and heart disease.

In the study, even after statistically adjusting for all the other factors affecting heart disease risk - - including weight, smoking, cholesterol levels, and blood pressure -- women with hypothyroidism were 70 percent more likely to have hardened aortas -- the body's main artery -- than those with normal hormone activity. They also had more than twice the risk of heart attack. Having autoimmune hypothyroidism increased the risk even further.