Updated March 08, 2014.

More than ten million Americans with high cholesterol levels may not know that their cholesterol is elevated due to undiagnosed thyroid problems.

High cholesterol affects an estimated half the American population, and is a major contributor to heart disease, America's number one killer. But the most commonly known cholesterol raisers -- diet or insufficient exercise - are not necessarily the problem for everyone.


Undiagnosed and undertreated hypothyroidism can cause elevated cholesterol, and of the estimated 27 to 59 million Americans with thyroid disease, at least half are undiagnosed and millions more are not sufficiently treated, opening them up to the risk of continued hypothyroidism symptoms despite treatment.

Some experts even believe that the numbers of undiagnosed are underestimated, and that the current thyroid diagnostic criteria are too narrow and rigid, and are missing many millions more with subclinical and low-level hypothyroidism.

In January of 2009, as part of Thyroid Awareness Month, the American Association of Clinical Endocrinologists (AACE) released the results of a survey on the thyroid-cholesterol connection, looking at the connection between undiagnosed hypothyroidism and high cholesterol. The survey had several important findings:
 

• Fewer than half of the adults who had been diagnosed with high cholesterol know if they had ever been tested for thyroid disease, despite the well-documented connection between the two conditions.
   

• Ninety percent of those surveyed were unaware of the thyroid gland's impact on cholesterol regulation.

According to AACE's president at the time, Richard A. Dickey, M.D., "Patients who have been diagnosed with high cholesterol should ask their physician about having their thyroid checked. If they have an underlying thyroid condition in addition to their high cholesterol, the cholesterol problem will be difficult to control until normal levels of thyroid hormone are restored."

The National Cholesterol Education Program and the Food and Drug Administration recommend thyroid testing in patients with high cholesterol levels. The prescribing information for the popular cholesterol-lowering drugs also recommends that patients be tested for thyroid disease before beginning cholesterol-lowering drug therapy.

It's unclear why, given that guidelines strongly recommend thyroid testing, more doctors are not insisting on thyroid testing upon the finding of high cholesterol. This may be a result of the medical profession's general lack of understanding about thyroid disease, or the tendency of doctors and patients to write off general symptoms such as fatigue, weight gain, and depression, particularly in women.