Newswise — Individuals with subclinical hypothyroidism—a mildly underactive thyroid only detectable by a blood test—are twice as likely to develop heart failure, compared to those with normal thyroid levels, according to a new study being presented on Thursday, Oct. 4, at the 78th Annual Meeting of the American Thyroid Association (ATA) in New York. Heart failure, also called congestive heart failure, is when the heart can't pump enough blood to the body's other organs, which can cause fatigue, ankle swelling and shortness of breath.

Although previous studies have shown that hyperthyroidism—an overactive thyroid—and hypothyroidism can cause heart problems, this is the first time that a large study found a negative effect on heart function when the thyroid was only mildly under-active.

"If other studies confirm these findings, then physicians might want to consider treating mild thyroid problems to prevent potential cardiac problems or to avoid increasing the severity of an existing heart condition," said Doug Bauer, M.D., an author of the study and a Professor of Medicine, Epidemiology and Biostatistics at the University of California at San Francisco School of Medicine in San Francisco.

Subclinical thyroid disorders are detected by a blood test that evaluates the levels of thyroid-stimulating hormone (TSH). Subclinical hypothyroidism is defined by TSH levels greater than 4.5 mU/L and normal free thyroxine levels. Individuals with subclinical hypothyroidism can evolve into overt hypothyroidism, where the free thyroxine levels fall below normal, which always requires thyroid hormone therapy.

The Cardiovascular Health Study involved over 3,000 adults 65 years and older, who were evaluated to determine if those individuals who had subclinical hypothyroidism had an increased risk of developing heart failure over a twelve-year period. The study shows that individuals who had a TSH level equal or greater than 10 mU/L had a two-fold risk of developing heart failure, compared to those who had normal thyroid levels.

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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.

The 78th annual meeting of the ATA will be in New York City from October 3-7, 2007 at the Sheraton New York Hotel & Towers. All program information is available at 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.

Thyroid diseases are among the most common disorders of the endocrine system, affecting almost 13 million Americans alone. The ATA has extensive online information for patients on thyroid disease (in English and Spanish) serving the clinician as a resource for patients and the public who look for reliable information on the internet. To further benefit patients, the ATA Alliance for Patient Education was formed in 2002 to offer an exchange of information between the ATA and four patient groups: Thyroid Foundation of America, ThyCa: Thyroid Cancer Survivors, Inc.; the Light of Life Foundation, and the National Graves' Disease Foundation. A public forum is held each year in conjunction with the ATA annual meeting.

Thyroid Research grants total over $200,000 annually to young investigators.

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American Thyroid Association Annual Meeting