A less severe condition known as subclinical hypothyroidism occurs in 10% of women in their 60s and 70s, and appears to increase the risk of heart disease. In subclinical hypothyroidism, patients have signs of thyroid malfunction on blood tests, but do not experience any obvious symptoms. 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 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.

The researchers estimate that subclinical hypothyroidism was the cause of 14% of all heart attacks in the study sample, a contribution just slightly less than other major risk factors, such as high cholesterol, smoking, high blood pressure, and diabetes. 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 Dr. Paul Ladenson, a thyroid specialist at Johns Hopkins University, hypothyroidism may be more common than currently thought. Ladenson‘s own studies indicate that as many as 17 percent of older American women in the United States may have the condition.

(See full-text original article from the Annals of Internal Medicine).

What is of special concern, though, is that many people whose test results are dismissed as normal could continue to have symptoms of an underactive thyroid. Their moods, emotions, and overall well-being are affected by this imbalance, yet they are not receiving the care they need to get to the root of their problems....Even if the TSH level is in the lower segment of the normal range, a person may still be suffering from low-grade hypothyroidism... What‘s clear is that serious consideration should be given to instituting hypothyroidism screening for all older women, and that efforts should be made to determine the optimal TSH ranges at which the risks of complications such as heart disease or hardening of the arteries is reduced.

Annals of Internal Medicine February 15, 2000;132:270-278