MedKoo Product Information:

Alfacalcidol 

Alfacalcidol is an active metabolite of Vitamin D, which performs important functions in regulation of the calcium balance and the bone metabolism. Alfacalcidol is Vitamin D-hormone analog which is activated by the enzyme 25-hydroxylase in the liver for systemic and in osteoblasts for local D-hormone actions. It possesses a unique pattern of pleiotropic effects on, e.g. gut, bone, pararthyroids, muscle and brain. Alfacalcidol is superior to plain vitamin D (cholecalciferol) because the final kidney activation of the latter is regulated by a negative feedback mechanism.

Alfacalcidol (or 1-hydroxycholecalciferol) is an analogue of vitamin D. Used for supplementation in humans and as a poultry feed additive. It has less of an effect on calcium metabolism than calcitriol, while having more potent effects on parathyroid hormone levels[2] and immune system, including regulatory T cells. Considered to be a more useful form of vitamin D supplementation, mostly due to much longer half-life and lower kidney load. Used as a poultry feed additive, it prevents tibial dyschondroplasia and increases phytate bioavailability. (http://en.wikipedia.org/wiki/Alfacalcidol).