ATA News Release 2004

Thyroid Problems Increase Risk of Heart Disease and Death

(VANCOUVER, BC, Oct. 1, 2004)—Individuals with subclinical hypothyroidism — an underactive thyroid only detectable by a blood test — have twice the risk of developing heart disease compared to those with normal levels of thyroid-stimulating hormone (TSH), according to a new study being presented on Friday, Oct. 1, at the 76th Annual Meeting of the American Thyroid Association in Vancouver, British Columbia, Canada. In addition, individuals with an overactive thyroid have a higher risk of dying from cardiovascular disease as well as all causes.

“Our findings also suggest that it may be worthwhile to screen those with heart disease for thyroid dysfunction by measuring their TSH levels,” said John P. Walsh, MBBS, PhD, an endocrinologist and Clinical Senior Lecturer in the Department of Endocrinology & Diabetes at Sir Charles Gairdner Hospital in Nedlands, Western Australia, “as subclinical hypothyroidism cannot be reliably detected by physical examination alone.”

There have been few large epidemiological studies examining the effects of thyroid dysfunction on cardiovascular disease, and it has been controversial whether subclinical hypothyroidism increases cardiovascular risk. Therefore, Dr. Walsh and colleagues conducted a community-based study in Western Australia, using data and 2,115 stored blood samples from the 1981 Busselton Health Survey.

Earlier this year, the researchers analyzed the data from 1981 — called a cross-sectional analysis — to assess the relationship of thyroid function with cardiovascular risk factors and the presence of coronary artery disease. They also conducted a 20-year longitudinal analysis using vital statistics and hospital admission information from an ongoing database. In the cross-sectional analysis, Dr. Walsh and colleagues found that individuals with subclinical hypothyroidism are two times as likely to develop coronary artery disease. In the longitudinal analysis, they found a two-fold increase in the incidence of coronary artery disease over a 20-year period.

“This is the first time that a significant increase in coronary artery disease associated with subclinical hypothyroidism has been demonstrated in a longitudinal study,” added Dr. Walsh. “These results strengthen the argument for treating patients with subclinical hypothyroidism rather than simply monitoring them.”

In addition, subclinical hypothyroidism — indicated by a raised TSH but normal thyroxine levels — was associated with an increase in cholesterol levels. This finding applied both to mild subclinical hypothyroidism with TSH between 4 and 10 mU/L and to subclinical hypothyroidism with TSH>10 mU/L. “Until now,” said Dr. Walsh, “there has been uncertainty whether cholesterol really is higher in those with a TSH between 4–10 mU/L.”

The study also found that hyperthyroidism — an overactive thyroid — is associated with increased overall and cardiovascular mortality. Dr. Walsh noted that this finding has been shown before but not in an unselected population as in this study. In this study population, the overall death rate was increased four-fold and cardiovascular mortality six-fold. Moreover, the increase remained significant after adjustment for age, sex and cardiovascular risk factors.

# # #