Subclinical Thyroid Dysfunctions Increase Risk of All-Cause Death

People with subclinical hyperthyroidism and subclinical hypothyroidism are at increased risk of all-cause death compared with people who have normally functioning thyroid, according to data presented on Oct. 2, 2008 at the 79th Annual Meeting of the American Thyroid Association (ATA) in Chicago, IL. In addition, people with subclinical hyperthyroidism are also at increased risk of cardiovascular death compared with people who have normal thyroid function.

Subclinical hyperthyroidism is a condition in which the thyroid is mildly overactive. Subclinical hypothyroidism is a condition in which the thyroid in mildly underactive. Both conditions have minor or no symptoms of thyroid disease and are detectable only through blood tests. Experts have not reached a consensus regarding whether to treat people with these subclinical thyroid dysfunctions (STD).

Researchers from the Faculdade de Medicina de Marilia in Marilia, Brazil and the Federal University of Sao Paulo in Sao Paulo, Brazil conducted a large prospective study of 1,110 individuals with normal thyroid function, hyperthyroidism, subclinical hyperthyroidism, hypothyroidism, and subclinical hypothyroidism to determine the relationship between STD and cardiovascular mortality and STD and all-cause mortality. Study participants were recruited from Japanese-Brazilians living in Brazil, were over the age of 30, and were not taking thyroid medication. Study participants were followed for up to seven years (2000-2007).

Researchers found that people with subclinical hyperthyroidism or subclinical hypothyroidism were at significantly increased risk of all-cause mortality compared with people with normal thyroid function. Researchers found that people with subclinical hyperthyroidism also had a significantly increased risk for cardiovascular mortality compared with people with normal thyroid function. In addition, researchers found that people with normal thyroid function survived longer than people with either subclinical hyperthyroidism or subclinical hypothyroidism.

“Until now, there has been uncertainty regarding the influence of STD on all-cause mortality and cardiovascular mortality,” said Dr. Jose Augusto Sgarbi of Faculdade de Medicina de Marilia, principle investigator of the study. “Our findings point to the need for a more aggressive treatment approach to people with subclinical hyperthyroidism and subclinical hypothyroidism to prevent all-cause mortality and cardiovascular mortality.”

About the American Thyroid Association (ATA)
The American Thyroid Association (ATA) is the lead organization in promoting thyroid health and understanding thyroid biology. The ATA values scientific inquiry, clinical excellence, public service, education, collaboration, and collegiality.

A non-profit medical society founded in 1923, the ATA fulfills its mission through supporting excellence and innovation in research, clinical care, education, and public health. ATA members are physicians and scientists who work to enhance the understanding of thyroid physiology and pathophysiology, improve the diagnosis and treatment of thyroid diseases, and promote the education of physicians, patients, and the public about thyroid disorders.