Chronic Excess Iodine Intake Inhibits Bone Reconstruction Leading to Osteoporosis in Rats.

BACKGROUND:Although iodine modulates bone metabolism in the treatment of thyroid disease, the effect of iodine intake on bone metabolism remains less known. OBJECTIVE:This study evaluated the effect of excess iodine intake in rats on bone reconstruction in the 6th and 12th month of intervention. METHOD:Rats were treated with different doses of iodinated water: the normal group (NI, 6.15 μg/d), 5-fold high iodine group (5HI, 30.75 μg/d), 10-fold high iodine group (10HI, 61.5 μg/d), 50-fold high iodine group (50HI, 307.5 μg/d), and 100-fold high iodine group (100HI, 615 μg/d). Thyroid hormone concentrations were determined by a chemiluminescent immunoassay. Morphometry and microstructure of bone trabecula were observed by hematoxylin and eosin staining and microcomputed tomography, respectively. Alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) staining were performed to evaluate the activity of osteoblasts and osteoclasts, respectively. RESULTS:The 24-h urine iodine concentration increased with iodine intake. The rats in the HI groups had higher serum thyroid-stimulating hormone and decreased serum free thyroxine concentrations in the 12th month than the NI group (all P < 0.05). The percentage of the trabecular bone area and osteoblast perimeter in the 100HI group were significantly lower than those in the NI group (P < 0.05). Increased structure model index was observed in the 50HI and 100HI groups compared with the NI group in the 6th month and increased trabecular separation in the 12th month (all P < 0.05). ALP and TRAP staining revealed osteoblastic bone formation was reduced, and the number of TRAP+ multinucleated cells decreased with increasing iodine intake. CONCLUSIONS:Excess iodine intake may increase the risk of hypothyroidism in rats. Chronic excess iodine intake can lead to abnormal changes in skeletal structure, resulting in reduced activity of osteoblasts and osteoclasts, which inhibits the process of bone reconstruction and may lead to osteoporosis.