Thyroid-Heart Risks Become Clearer

Study Questions Heart Benefits of Treating Mildly Underactive Thyroids

Medically Reviewed by Louise Chang, MD on February 28, 2006

Feb. 28, 2006 -- The thyroid's heart effects are getting a fresh look in a new study.

The thyroid gland is a butterfly-shaped gland at the base of the neck. It makes hormones that influence metabolism.

The new study followed more than 3,200 senior citizens for more than 12 years. The findings:

  • Most people had normal thyroid activity.
  • People with mildly overactive thyroids were more likely to develop atrial fibrillation, a type of irregular heart rhythm.
  • Treating mildly underactive thyroids didn't appear to bring heart benefits.


The data supports heart benefits for treating mildly overactive thyroids, but not mildly underactive thyroids, write the University of Pennsylvania's Anne Cappola, MD, ScM, and colleagues.

Their study appears in The Journal of the American Medical Association.

Thyroid Problems

Most people have thyroids that work normally. However, some people have underactive thyroids (hypothyroidism) and others have overactive thyroids (hyperthyroidism) to varying degrees.

Such thyroid problems can be treated. But the heart benefits of doing so have been unclear, write Cappola and colleagues.

"It's our wish to figure out ... which thyroid level is associated with the highest level of function," Cappola says, in a news release referring to heart function.

"Many patients with mild thyroid problems are being treated now and it's not clear if it's actually helping them," Cappola continues, still speaking about heart benefits. "We need to put together a bigger picture for the risks and benefits of treatment for mild thyroid abnormalities."

Looking for Patterns

At the study's start, the seniors had their thyroids tested.

Most (82%) showed normal thyroid activity. Fewer people (15%) had mildly underactive thyroids. About 1.5% had mildly overactive thyroid activity.

Cappola's team didn't assign anyone to get thyroid treatments. That decision was up to each participant and their doctors. The researchers just tracked participants' heart health, looking for any patterns with thyroid status.

The study covered problems including heart disease, atrial fibrillation, heart attack, heart bypass, coronary angioplasty (reopening of narrowed or blocked blood vessels that supply blood to heart muscle), and stroke.

Study's Results

Atrial fibrillation was the only heart problem associated with thyroid woes. That pattern was only seen in people with mildly overactive thyroids.

Mildly underactive thyroids weren't linked to higher risk of any heart problems. During the study, 27% of people with mildly underactive thyroids sought thyroid treatment. They didn't show any change in heart risk, for better or worse, the researchers write.

Thyroid problems weren't associated with the risk of dying during the study, the researchers write.

Cappola and colleagues say the heart benefits of treating thyroid problems have been unclear in the past. In their study, they reached these conclusions:

  • Treating seniors with mildly overactive thyroids could help prevent atrial fibrillation.
  • Their data didn't support treating mildly underactive thyroids for the heart's sake.


Remember, the study only looked at heart health and didn't directly look at people's thyroid treatments. In underactive or overactive cases, lab tests are checked periodically to monitor status. Thyroid problems may need treatment for other reasons not covered in Cappola's study.

Show Sources

SOURCES: Cappola, A.The Journal of the American Medical Association, March 1, 2006; vol 2905: pp 1033-1041. WebMD Medical Reference: "Understanding Thyroid Problems." WebMD Medical Reference from Healthwise: "Atrial Fibrillation: Overview." News release, University of Pennsylvania School of Medicine. News release, JAMA/Archives.
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