Effect of cholecalciferol, 1,25(OH)2D3 and zinc on bone metabolism in the rat

An experiment was conducted using young adult female rats to compare the effects of dietary 1,25 dihydroxycholecalciferol (1,25(OH)2D3) and vitamin D3 on zinc retention in bone and to determine whether the level of dietary zinc affected the rate of bone turnover. Ninety 8 week old female rats were with 3H-tetracycline and fed a purified low calcium egg white diet (EWD) for 8 weeks. The dietary groups were as follows: EWD containing 4.5, 10, 100 or 200 mg Zn/kg diet plus vitamin D3 and EWD plus 4.5, 10, 100 or 200 mg Zn/kg diet plus 1,25(OH)2D3. The results show that the form of vitamin D3 affected zinc uptake by the femur. Bone zinc concentrations were consistently higher when 1,25(OH)2D3 instead of cholecalciferol was the source of vitamin D3 steroid. Elevating dietary zinc up to 100 or 200 mg/kg diet resulted in increased bone resorption as measured by the 3H-tetracycline loss. Resorption of bone calcium was reduced when 1,25(OH)2D3 was fed with either 4.5 or 10 ppm zinc. High levels of dietary zinc caused increased bone resorption and counteracted the reduction of bone catabolism seen with 1,25(OH)2D3 at low or required zinc levels. Serum 1,25(OH)2D3 was significantly elevated with increased dietary zinc. These data indicate that high but non-toxic dietary levels of zinc may be an additional factor enhancing bone loss when calcium intake is low. The vitamin D3 steroid, 1,25(OH)2D3, had a marked inhibitory effect on bone resorption and appears to enhance the accumulation of zinc and calcium in bone of young adult female rats.