Slightly-overactive thyroid tied to heart problems

A new report suggests higher-than-normal thyroid activity is linked to a greater risk of heart disease, including irregular heartbeats.

People with so-called subclinical hyperthyroidism have a slightly-overactive thyroid - a gland at the front of the neck responsible for regulating metabolism by releasing certain hormones.

Those people often don't have the typical signs of full-on hyperthyroidism, such as increased appetite, restlessness and fatigue - so the condition may frequently go undiagnosed.

Because many patients just outside the normal range are older and their thyroid function and hormones can naturally fluctuate, doctors have wondered whether or not it's helpful to treat them with thyroid drugs.

"There's been a discussion by many of us about what we should do with subclinical hyperthyroidism, because the risks were unclear," said Dr. Nicolas Rodondi from the University of Bern, Switzerland, who worked on the report.

Slightly-overactive or underactive thyroids are much more common than overt thyroid disease, researchers said.

Full hypo- and hyperthyroidism have been clearly tied to the body's inability to regulate its normal functions, and can be treated with medication or surgery.

Rodondi's study, published in the Archives of Internal Medicine on Monday, suggests subclinical hyperthyroidism may in fact carry extra risks of its own.

In an analysis of previous trials including over 50,000 older adults, people whose hormone tests showed slight hyperthyroidism were 29 percent more likely to die of heart disease over the next nine years than those with normal thyroid function.

Subclinical hyperthyroidism was also tied to a higher risk of irregular heartbeat - but not to stroke or cancer, Rodondi and his colleagues reported.

Rodondi's group defined "normal" thyroid function as blood levels of thyrotropin, also known as thyroid stimulating hormone (TSH), between 0.45 and 4.49 milli-international units per liter.

The normal range for TSH itself remains a topic of debate, however, with some experts favoring a narrower definition of 0.3 to 3.0 mIU/L. That would potentially give some 20 percent of Americans "abnormal" TSH levels.

Subclinical Hyperthyroidism and the Risk of Coronary Heart Disease and Mortality

Conclusions Endogenous subclinical hyperthyroidism is associated with increased risks of total, CHD mortality, and incident AF, with highest risks of CHD mortality and AF when thyrotropin level is lower than 0.10 mIU/L.

Tinh-Hai Collet, MD; Jacobijn Gussekloo, MD, PhD; Douglas C. Bauer, MD; Wendy P. J. den Elzen, PhD; Anne R. Cappola, MD, ScM; Philippe Balmer, BSc; Giorgio Iervasi, MD; Bjørn O. Åsvold, MD, PhD; José A. Sgarbi, MD; Henry Völzke, MD; Baris Gencer, MD; Rui M. B. Maciel, MD; Sabrina Molinaro, PhD; Alexandra Bremner, PhD; Robert N. Luben, PhD; Patrick Maisonneuve, Ing; Jacques Cornuz, MD, MPH; Anne B. Newman, MD, MPH; Kay-Tee Khaw, MD; Rudi G. J. Westendorp, MD, PhD; Jayne A. Franklyn, MD, PhD, FRCP, FMedSci; Eric Vittinghoff, PhD; John P. Walsh, MBBS, FRACP, PhD; Nicolas Rodondi, MD, MAS; for the Thyroid Studies Collaboration