Similar to vitamin D2, vitamin D3 undergoes metabolic processes in the liver and kidneys to become biologically active. In the liver, vitamin D3 is hydroxylated to form 25-hydroxyvitamin D3 (25(OH)D3) ...
The recommended daily intake of 10 micrograms is based on estimates of the amount required to keep blood levels of serum 25-hydroxyvitamin ... are best. Is D2 or D3 a better supplement?