THYROID-HORMONES AND SELENIUM STATUS IN BREAST-CANCER

Within a case-control study of postmenopausal breast cancer patients ( n = 99) and matched healthy controls (n = 105), thyroid hormone levels were compared and correlated with toenail selenium concentrations. Pl asma triiodothyronine (T-3) was significantly lower in cases (1.4 +/- 0.4 nmol/l) than in controls (1.6 +/- 0.4 nmol/l), and a strong invers e relationship with breast cancer was observed with an odds ratio of 0 .17 (95% CI = 0.08-0.36) in the highest compared with the lowest terti le of T-3. Plasma thyroxine and thyroid-stimulating hormone concentrat ions were similar between cases and controls. Plasma T-3 concentration was positively associated with toenail selenium in cases (age-adjuste d regression coefficient = 0.049) and controls (age-adjusted regressio n coefficient = 0.036). Toenail selenium concentrations tended to be l ower in cases than in controls, but the differences did not Peach stat istical significance. Although the disease process per se may explain the lower plasma T-3 concentrations, it is also possible, inasmuch as these patients were in early-stage breast cancer, that selenium status may be influencing T-3 levels via changes in the activity of the sele noenzyme type I iodothyronine deiodinase.