http://www.drugbank.ca/drugs/DB01436

^^^ Gotta check that out^^^ What an awesome website!

http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=2091

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.

D3 is cholecalciferol, not calcitriol, which is the more active form. Read more, mid-way down the page: http://suppversity.blogspot.ca/2012/09/on-short-notice-250-more-testosterone.html

I never heard about Alfacalcidol. How Paleo gurus missed it? Is this new to supplements world?

Alfacalcidol is a type of vitamin D used to treat a number of conditions such as osteomalacia (rickets), familial hypophosphatemia, hypoparathyroidism, osteodystrophy, vitamin D deficiency, and so on. Also, this medication is used to increase the levels of vitamin D, calcium, and phosphate in the body. It belongs to a group of medicines called vitamin D analogues.