Biological activity of 1-alpha-hydroxy vitamin D3 in vitamin D dependency

The biological activity of 1(OH) vitamin D3 was evaluated in 2 cases of vitamin D dependency. For the improvement of serum chemistry and increment of urinary excretion of calcium 1(OH) vitamin D3 was 500--1000 times more active than vitamin D2. The administration of 0.05 microg/kg/day and 0.1 microg/kg/day of 1(OH) vitamin D3 were equally effective to keep the serum chemistry within normal limits. However, urinary excretion of calcium increased to an abnormal height on 0.1 microg/kg/day of 1(OH) vitamin D3. On the other hand, administration of 0.05 microg/kg/day of 1(OH) vitamin D3 kept both serum level and urinary excretion of calcium normal. It is suggested that 0.05 microg/kg/day is close to the optimum requirement of 1(OH) vitamin D3 in vitamin D dependency and this should correspond to the essential requirement of 1(OH) vitamin D3 in man.