The effects of high calcium intake on the activity of thyroid gland in rats

The effects of goitrogens on the thyroid gland have been much studied and calcium is considered as a goitrogen in some cases. Since the level of calcium is high in drinking water of some cities of Khozestan province, the effects of high calcium intake on the function of thyroid gland is investigated in this study. For this purpose the concentration of thyroid hormones is measured in rats. The study was carried out on 73 male and female rats. The animals were divided into 3 groups, control group with nonnal diet (n=25), group 2 (n=24) consumed diet with high calcium (1 g/kg diet) and group 3 (n=24), had diet with high calcium and iodine (50 µg/kg diet). Animals had free access to diet and water. The rats were decapitated after 1.5 and 3 months, blood samples were collected, centrifuged and the sera were stored at -20°C. Hormones (T3, T4 and TSH) and T3 uptake were measured by radioimmunoassay method, using commercially available kits (Kodak, England). The results indicated that the amount of T3 in the test group was not significantly different from that of control group. The results showed that in the groups which consumed diet containing high calcium and iodide, mean total T4 concentration was significantly higher than control (p<0.05). Measurement of T3 uptake showed that in the test groups, T3 uptake was significantly lower than control. This may be due to increased synthesis of proteins, less hormone synthesis, or abnormality of the protein binding to the hormones. In general the results are predictable with the known concepts.