Bioeffect and safety of long-term feeding of common salt fortified with iron and iodine (double fortified salt) in rat

A doubly fortified salt formulation developed at NIN as a public health measure for combating iron deficiency anemia and iodine deficiency disorders was evaluated for its efficacy and safety in experimental rats. The hemoglobin regenerating ability of diet with double fortified salt (DFS) containing 1000 ppm iron, 30 ppm iodine and 1% of sodium hexametaphosphate (SHMP), as the stabilizer, was compared to that of diets with iron fortified salt (IFS 1000 ppm) and unfortified salt in rat model using a depletion-repletion method. The safety and long-term feeding of DFS in relation to calcium and phosphorus metabolism was also tested. The results revealed that the amounts of hemoglobin regenerated in both the supplemented salt fed groups (DFS: 13.0 +/- 1.4 and IFS: 11.7 +/- 1.4 g/dl) were significantly higher than that in the unsupplemented group (7.6 +/- 4.0 g/dl) at the end of 4 weeks. Though an increase in the excretion of iodine was seen in DFS fed group (5.2 +/- 5.2 mu g I/day) compared to IFS fed group (1.3 +/- 0.45 mu g I/day) at the end of 9 months, it was not statistically significant and also both the groups had comparable hemoglobin levels (15 g/dl) and liver iron content (73 mu g iron/g liver). Serum alkaline phosphatase (164 +/- 6.7 vs 132 +/- 25.2 IU/L) and calcium (10.1 +/- 0.6 vs 10.2 +/- 0.9 mg/dl) and urinary phosphate (12.1 +/- 4.2 vs 11.4 +/- 2.5 mg/day), calcium (5.4 +/- 3.2 vs 5.1 +/- 1.9 mg/day) and creatinine (9.3 +/- 2.3 vs 8.3 +/- 1.5 mg/day) were found to be similar in DFS and IFS groups, at the end of 9 months of feeding the respective diets. However, there was a significant increase in serum phosphate (11.4 +/- 0.7 vs 7.2 +/- 0.7 mg/dl P<0.01) in the DFS fed group as compared to the IFS fed controls. Whole body x-ray of the DFS and control groups suggested no gross bone abnormality. Histopathological examination of major organs did not indicate any differences between the two groups. Thus, the study revealed that the iron provided through DFS is bioavailable. SHMP per se had no effect on calcium and phosphorus metabolism, except for an increase in serum phosphorus, the significance of which is not known. However, all the other indicators tested showed no evidence of any toxicity due to the long term consumption of DFS. (C) 1998 Elsevier Science Inc.