PISA, ITALY. Thyroid hormones act directly on the heart to control heart rate and force of contraction. The biologically active hormone triiodothyronine (T3) is mostly (80%) formed in peripheral conversion of the prohormone thyroxine (T4). Research has shown that heart attack patients and patients with heart failure often have very low levels of circulating T3. Researchers at the National Council Research Institute of Clinical Physiology now report that low T3 levels are a strong indicator of early death in heart disease patients.
Their study involved 573 heart disease patients (most with heart failure or a former heart attack) who had
their T3 levels measured between January 1, 1999 and January 1, 2000. The patients were divided into two
groups. Group 1 (173 patients) with a free T3 level less than 3.1 pmol/L and group 2 (400 patients) with a
T3 level greater than or equal to 3.1 pmol/L. During the year following T3 measurement 25 patients in group
1 died (14.4%) versus only 12 patients in group 2 (3%). There were 13 cardiac deaths (7.5%) in group 1
and 6 (1.5%) in group 2. The researchers conclude that a low T3 level is a strong risk factor for early death
in heart disease. They also suggest that long-term T3 replacement therapy may be beneficial for heart
disease patients, but caution that large scale studies will be required to prove or disprove this.