Researchers at the University of Pennsylvania School of Medicine have found that leaving a mildly underactive thyroid gland (subclinical hypothyroidism) untreated does not lead to increased cardiovascular risk. The study results, to be published in the March 1, 2006 issue of the Journal of the American Medical Association, may lead to changes in the clinical treatment of this commonly diagnosed ailment.
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.�
Some organizations recommend that practitioners screen all patients over a certain age periodically for thyroid dysfunction. Cappola disagrees:
“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. There’s no evidence you should treat someone with a mildly underactive thyroid in order to help deter cardiovascular disease.�
The findings, however, contradict a number of other studies that have shown cardiac benefits to treatment of mild or subclinical hypothyroidism. For example, a study reported on in the November 2005 issue of the Archives of Internal Medicine was one of the first large studies to look at the connection between thyroid dysfunction and heart disease, and in particular, the question of whether subclinical hypothyroidism is a risk factor for development of heart disease. Researchers found that patients with subclinical hypothyroidism had a much higher rate of heart disease than those with normal thyroid levels.
That same issue of the Archives of Internal Medicine also found that among a group aged 70 to 79, compared to patients with normal thyroid function, congestive heart failure occurred more often in those with a TSH level of 7.0 or hgher, but not among those with 4.5-6.9 TSH.
Clearly, the issue of the impact of mild hypothyroidism on heart disease is now in a controversial thyroid topic, and more research is needed to explore this further and provide more definitive findings.
Mary Shomon, About.com's Thyroid Guide since 1997, is a nationally-known patient advocate and best-selling author of 10 books on health, including "Living Well With Hypothyroidism," and "Living Well With Graves' Disease and Hyperthyroidism." Click here for more information on Mary Shomon.
