Subclincial hyperthyroidism not associated with overall or cardiovascular mortality

"Hyperthyroidism is associated with a number of health concerns, chief among them being cardiovascular disease. Though subclinical hyperthyroidism mimics some of the features of classic hyperthyroidism, new data show that a link to cardiovascular disease is not one of them," said Douglas Forrest, PhD, of the National Institute of Diabetes and Digestive and Kidney Diseases, and Program Co-Chair of the ATA Annual Meeting.

Subclinical hyperthyroidism is a mild form of hyperthyroidism that affects approximately 1-2% of men and women ages 65 and older. Unlike classic hyperthyroidism, in which a person's thyroid hormones are high, people with subclinical hyperthyroidism have low-levels of thyroid-stimulating hormone (TSH) levels but normal levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). The degree to which subclinical hyperthyroidism persists over time as well as its associated health risks were heretofore unknown.

A team of researchers led by Paige Fortinsky, MD, at the University of Pennsylvania Medical Center in Philadelphia thus undertook a study to examine transitions in the thyroid status over a 2-3-year period and determine the risks of cardiovascular and total mortality in older individuals with subclinical hyperthyroidism. They enrolled 5,009 men and women aged 65 and over who were enrolled in the Cardiovascular Health Study and not taking thyroid medications. They identified 70 subjects with subclinical hyperthyroidism (TSH < 0.45 mU/L with a normal free-T4 level) at their first TSH measurement and examined persistence, resolution, and progression of subclinical hyperthyroidism over 2-3 years.

Of the 70 individuals with subclinical hyperthyroidism, 60% were women, 24% were nonwhite, and their mean age was 73.7 years. Among those with subclinical hyperthyroidism who obtained follow-up thyroid testing or were taking thyroid medication at follow-up (n=44), 43% persisted, 41% reversed to normal levels of thyroid hormone, 5% progressed to overt hyperthyroidism, and 11% initiated thyroid medication. Researchers analyses' found no association between subclinical hyperthyroidism and total or cardiovascular mortality.