http://ajcn.nutrition.org/content/88/2/491S.long

This article dates back to 2007 (took me a while to find it in my archives).

The body regulates how much Vitamin D3 is converted into an active form according to nutritional status and need. That activated form behaves like both a steroid & a hormone; depending upon the target organs and tissues. Even now, research is ongoing in an attempt to determine all the effects that the activated form may have on tissues, organs and organ systems.

It makes me wonder if supplementing with more than is needed may have unwanted side effects down the road. Does the body only activate what is needed from the supplement, or does the supplemented D3 have a steroidal & hormonal effect?
Given that the jury is still out on that, it may be wise to remain within a reasonable amount of supplemental Vitamin D3, with the dose required, determined by blood tests. More than what is needed to correct a deficiency might have unwanted side effects over the long term.

Mega dosing of Vitamin C revealed problems a couple of decades ago; when long term, high dose takers developed kidney stones, decreased bone density and dental problems due to acidosis. It was found that the body attempted to buffer the acidosis by releasing stored calcium from bones & teeth and some of that released calcium precipitated in the kidneys.
Now we know that Calcium ascorbate, rather than ascorbic acid is a superior supplemental form of Vitamin C...but it took quite a while to figure out.

With love, Erika