No Increased Cardiovascular Risk If Mildly Underactive Thyroid Left Untreated, Study Finds

The thyroid gland, located at the base of the neck, produces thyroid hormone, which acts throughout the body to regulate metabolism. Patients with underactivity of the thyroid gland, or hypothyroidism, may suffer from a variety of symptoms affecting the functions of the body. These patients are typically treated with medication to increase the thyroid hormone in the body. Likewise, patients with overactivity of the thyroid gland, or hyperthyroidism, may also be symptomatic and require treatment to lower their thyroid hormone levels.

In general, mild thyroid problems are common and often the symptoms can be subtle. It's still unclear exactly who needs to be checked for it and what the risks and benefits of treatment are. Researchers aren't sure whether treating a patient with a mild thyroid problem actually helps them.

"Previous studies have suggested that abnormal levels of thyroid stimulating hormone may represent a cardiac risk factor, the way that increased cholesterol or smoking are risk factors for heart disease." said lead author Anne Cappola, MD, ScM, Assistant Professor of Medicine and Epidemiology. "We set out to answer the question of whether there are cardiovascular consequences resulting from mild thyroid problems."

In this study, Cappola measured thyroid function through a blood test in 3200 men and women, aged 65 and older. These were people who had no reason to have an abnormal test and were not taking thyroid hormone replacement. She categorized them into different groups based on their thyroid blood tests and followed them for 13 years. Cappola found that 1.5% of the group who had a mildly overactive thyroid (subclinical hyperthyroidism) had an increased risk of developing an abnormal heart rhythm, atrial fibrillation, but no other cardiovascular threats such as heart attacks or death. Those with a mildly underactive thyroid gland made up 15 percent of the study, and showed no elevation in their risk of suffering a heart attack, stroke, or death.

Cappola adds, "It's our wish to figure out what is a normal number versus an abnormal number ... which thyroid level is associated with the highest level of function. Many patients with mild thyroid problems are being treated now and it's not clear if it's actually helping them. We need to put together a bigger picture for the risks and benefits of treatment for mild thyroid abnormalities."

So should general practitioners be screening patients over a certain age every so often for thyroid dysfunction? Some organizations recommend it. "We say there's no evidence, based on our data, that screening would benefit the population. But if you do find someone over the age of 65 with a mildly overactive thyroid, they should be treated," explains Cappola. "There's no evidence you should treat someone with a mildly underactive thyroid in order to help deter cardiovascular disease."

The results of this study will be published in the March 1st, 2006 issue of "JAMA." The article is titled, "Thyroid Status, Cardiovascular Risk and Mortality, in Older Adults."

This study was supported by an American Heart Association Grand-in-Aid; contracts from the National Heart, Lung and Blood Institute; and a grant from the National Institute on Aging.