Effects of humine compounds on iodine utilisation and retention and on the function of the thyroid gland

Abstract

Effects of sodium humate (HuNa), containing 61.9% of humic acids in dry matter, on utilisation and retention of dietary iodine were investigated in balance experiments carried out in pigs. A control group was fed a commercial diet containing 0.1 mg of iodine per kg. The daily intake of iodine was 129.2 µg per animal or 4.08 µg per kg live weight. The recommended intake of dietary iodine is 0.25 to 0.30 mg per kg at 88% dry matter. The experimental group (HuNa) was fed the same diet supplemented with 3% of sodium humate which contained 0.5 mg of iodine per kg at 90.04% dry matter. The supplementation increased the daily intake to 141.4 µg per animal, or 4.45 µg per kg live weight. The supplementation of HuNa increased significantly the amount of iodine excreted in faeces (53.2 ± 11.0 vs. 43.0 ± 6.47 µg per animal per day; P < 0.05) and nonsignificantly the urinary iodine excretion (31.8 ± 8.93 vs. 29.0 ± 11.3 µg per animal per day). Differences between the HuNa and the control groups in blood serum iodine concentrations (18.8 vs. 18.1 µg per litre) and urinary iodine concentrations (32.5 vs. 34.4 µg per litre) were nonsignificant. It is evident from the concentrations that the pigs suffered from a serious iodine deficiency. Compared with controls, the HuNa group showed significantly higher triiodothyronine concentration (P < 0.05) and nonsignificantly lower thyroxine and iodine concentrations in blood serum. Dietary iodine utilisation was lower in the HuNa than in the control group (62.3 vs. 66.6%). The results show that utilisation of dietary iodine was limited and that sodium humate (humic acids) reduced iodine utilisation and retention and affected also other parameters indicating their goitrogenic effects.