I'd take this writer with a shaker-full of salt. There is not necessarily a direct relationship between intake of "Vitamin D3" (cholecalciferol) and blood levels of the active/hormone form of the vitamin, 1,25-dihydroxycholecalciferol (which this writer is referring to as "1,25-dihydroxy D3").
If someone has begun ingesting thousands of units of cholecalciferol daily, and is still not getting normal blood levels of the 1,25-dihydroxy form (or even any increase at all, as the writer states), in the vast majority of cases this doesn't mean they need to up their intake of cholecalciferol. Much more likely, it means they have liver and/or kidney disease that is preventing them from converting as much of the inactive form to the active form as they need. And in that case, they need to be supplemented with the active form (which is available by prescription only, and is *very* harmful if taken excessively, because the body does not have any way of back-converting excess amounts).
If someone has begun ingesting thousands of units of cholecalciferol daily, and is still not getting normal blood levels of the 1,25-dihydroxy form (or even any increase at all, as the writer states), in the vast majority of cases this doesn't mean they need to up their intake of cholecalciferol. Much more likely, it means they have liver and/or kidney disease that is preventing them from converting as much of the inactive form to the active form as they need.
My first thought was the stuff was phony. I would have thought a doc testing for blood levels of 1,25-dihydroxy vitamin D would have blood chemistry tests indicating liver or kidney dysfunction/disease already.