calcitriol

That simply lists precursors to calcitriol, which you can get but isn't recommended because it is hard to dose.

The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol[1].

Normally your body converts D3 to calcitriol but those with certain diseases will not get it converted.

Vitamin-D2 aka ergocalciferol works similar in that is is eventually converted by liver and kidneys into calcitriol.

Cholecalciferol is used in over the counter supplements, not calcitriol (which is the active vitamin D form).

But those with certain diseases, the kidneys don't do the conversion so they provide vitamin D3 in the form called calcitriol.

A Doctor gave my cousin a prescription of Calcitriol because it was much more expensive.

Then, calcidiol is further converted to calcitriol, the active form, in the kidneys, which may take additional time.

So I have to take vitamin D, calcitriol and phosphrous binder and dietary restrictions to balance it all.

Apparently he is one the people who identified calcitriol in 1971.

These properties are shared by calcitriol and the CYP11A1‐generated non‐calcemic hydroxyderivatives.

The kidneys (mostly) then turn that in calcitriol, the actual hormon.

The closest thing I can find to a need to convert vitamin D into an "active form" is the conversion of cholecalciferol to calcidiol and thence calcitriol.

Regarding point 2: It's hard to get vitamin D toxicity because active vitamin D (calcitriol) is created "on demand" by cellular processes by tapping a much larger reserve of inert substance (calcifediol).

"But looking more closely at the increased deaths, they were mostly from autoimmune diseases that couldn’t plausibly be related to their donations." Kidneys make calcitriol.

And to reinforce the original point: Vitamin D helps calcium and phosphorus uptake in your system (really, it's crucial for it): "For example, some of the proteins produced in response to calcitriol in the intestine help transport calcium across the intestine and into the bloodstream, greatly increasing the absorption of calcium from the diet.

The active form of Vitamin D (Calcitriol) can be both helpful and harmful to bone health.

However that warning was for someone who goes out of way to acquire Calcitriol.

Calcitriol is actually the most confusing of my medications to manage since the dosage needs to be adjusted based on monthly blood tests.