My intention was that, “likely from the extra calcium” would be read somewhat ambiguously in terms of if it was extra calcium supplemented in the WHI trial, or extra calcium absorbed from food as a result of active vitamin D getting to the guts. So I don’t necessarily disagree with the possibility that it could be due to the vitamin D itself. That said, I want to protest that calcium levels in the blood do seem to be very tightly regulated. But I don’t think you need to assume that blood calcium levels vary? If you absorb extra calcium (either because you eat/supplement more or because you absorb more) then your kidneys need to excrete it. That seems like the most likely explanation to me.
My intention was that, “likely from the extra calcium” would be read somewhat ambiguously in terms of if it was extra calcium supplemented in the WHI trial, or extra calcium absorbed from food as a result of active vitamin D getting to the guts. So I don’t necessarily disagree with the possibility that it could be due to the vitamin D itself. That said, I want to protest that calcium levels in the blood do seem to be very tightly regulated. But I don’t think you need to assume that blood calcium levels vary? If you absorb extra calcium (either because you eat/supplement more or because you absorb more) then your kidneys need to excrete it. That seems like the most likely explanation to me.