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Should Doctors Treat Subclinical Hypothyroidism to Help Prevent Heart Disease?


Updated: May 30, 2007

Should Doctors Treat Subclinical Hypothyroidism to Help Prevent Heart Disease?
Heart disease is one of the major health challenges facing Americans. Now, researchers have found a thyroid-based treatment approach that may help reduce the risk of heart disease in some people.

Experts estimate that as many as 17 percent of the general population suffer from a mild form of underactive thyroid known as subclinical hypothyroidism. Typically, doctors have not treated subclinical hypothyroidism, claiming that there is no demonstrable benefit to patients.

It’s a controversial topic however, as some studies have shown that failing to treat subclinical hypothyroidism can have negative consequences. In particular, the relationship between untreated hypothyroidism and the risk of developing heart disease and metabolic syndrome has been a topic of some controversy.

The largest study to date on the topic was recently conducted, and the results were reported in the May 2007 issue of The Journal of Clinical Endocrinology & Metabolism. The researchers concluded that treating subclinical hypothyroidism can improve a number of heart disease risk factors, as well as certain quality of life measurements.

A Look at the Study

The two-phase study evaluated 100 people who were subclinically hypothyroid. During phase one, half the group received 100 mcg of the synthetic thyroid drug levothyroxine for 12 weeks, while the other half of the group received a placebo. Because this was a crossover study, at the end of the 12 week period, the placebo group received the levothyroxine, and the group receiving the thyroid drugs then received placebo for another 12 weeks.

During both phases, the following criteria were evaluated: cholesterol levels, a specific measurement of artery health known as "endothelial function," waist-to-hip ratio (a heart disease risk factor), body weight, and self-reported quality of life issues, (e.g., fatigue).

The Surprising Findings

According to the researchers, the group receiving levothyroxine treatment experienced the following effects:
  • reduced total cholesterol level - the study showed an 11 point reduction during the 12 weeks period on levothyroxine
  • a drop in low-density lipoprotein (LDL), also known as “bad" cholesterol
  • improved endothelial function, a marker for hardening of the arteries
  • a reduced waist-to-hip ratio
  • a reduction in body weight, on average 1.1 pounds
  • an improvement in feelings of tiredness
The researchers concluded that people who are subclinically hypothyroid could improve their heart disease risk factors and reduce tiredness after treatment with 100 mcg of levothyroxine.

What This Means for You

This research suggests that evaluation of both thyroid-stimulating hormone (TSH) and free T4 may be warranted in all adults, and especially in anyone at increased risk of heart disease.

Ultimately, if future research does find that treatment helps reduce heart disease risk in the long-term, thyroid testing could become a routine part of annual physicals for adults in the U.S.

In the meantime, a small but growing number of practitioners feel that the benefits of treatment outweigh any risks, and patients who are subclinically hypothyroid will find it somewhat easier to find practitioners who are willing to treat the condition.

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 Hormone Breakthrough: Overcoming Sexual and Hormonal Problems at Every Age," "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," and "Living Well With Chronic Fatigue Syndrome and Fibromyalgia." Click here for more information on Mary Shomon.


Razvi, Salman et. al. "The Beneficial Effect of L-Thyroxine on Cardiovascular Risk Factors, Endothelial Function, and Quality of Life in Subclinical Hypothyroidism: Randomized, Crossover Trial," The Journal of Clinical Endocrinology & Metabolism 92(5):1715–1723, Online: http://jcem.endojournals.org/cgi/content/abstract/92/5/1715

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