A new study in rats is giving researchers hope that more aggressive treatment of hypothyroidism and borderline hypothyroidism will result in a reduction of heart disease in human beings. Because roughly 10 percent of the U.S. population suffers from hypothyroidism or borderline hypothyroidism, the insufficient production of thyroid hormones, the teams discovery could potentially lead to improvement in patients with heart disease.
While further research is needed, results from a recent study entitled, Low Thyroid Function Leads to Cardiac Atrophy with Chamber Dilation, Impaired Myocardial Blood Flow, Loss of Arterioles, and Severe Systolic Dysfunction, suggest that low thyroid function has the potential to cause heart failure. The study was conducted by the Cardiovascular Research Institute-South Dakota Health Research Foundation, Sioux Valley Health System and The University of South Dakota School of Medicine.
We provided strong evidence that low thyroid function alone induced in rats eventually can cause heart failure, said Dr. A Martin Gerdes, director of the Cardiovascular Research Institute and co-author of the study. We also discovered that low thyroid function severely impaired cardiac blood flow due to a dramatic loss of the hearts small blood vessels (arterioles). Within six weeks after inducing low thyroid function in rats, half of the hearts small arterioles were gone.
The effects of hypothyroidism were studied in rats on a short-term (6 weeks) and long-term (1 year) basis. What the research team learned is that hypothyroidism led to severe, progressive contractile dysfunction, chamber enlargement, and ventricular wall thinning despite a reduction in cardiac mass. Hypothyroidism induced in the rats also resulted in impaired myocardial blood flow due to a dramatic loss of arterioles. As a result, the team identified two new mechanisms by which low thyroid function may lead to heart failure.
The study is particularly significant because it was not clear previously if low thyroid function alone can actually cause heart failure or was just another risk factor. While human data are not yet available, the link between low thyroid function and increased heart disease suggests that something like this could also be occurring in humans, Gerdes said. Since the rats in this study had relatively mild hypothyroidism, the results suggest that individuals with borderline hypothyroidism may also have similar cardiac changes. Clearly more research is needed to determine if these detrimental cardiac changes occur in humans and if treatment of heart patients with borderline hypothyroidism will lead to improved outcomes. In the absence of further research, however, Gerdes says some caution should be exercised since over treatment with thyroid hormones is known to cause adverse effects.
The Cardiovascular Research Institute (CRI) study is published in the Nov. 15 issue of Circulation, the journal of the American Heart Association. The study can be viewed online.
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 "The Thyroid Diet: Manage Your Metabolism for Lasting Weight Loss," "Living Well With Hypothyroidism: What Your Doctor Doesn't Tell You...That You Need to Know," "Living Well With Graves' Disease and Hyperthyroidism," "Living Well With Autoimmune Disease," "Living Well With Chronic Fatigue Syndrome and Fibromyalgia," and the "Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success." Click here for more information on Mary Shomon.