"That sunlight is needed is not a MAJOR flaw in the sense that it disproves Marshall's proposal. Rather it's just one explanation for what we observe." Disagree. Marshall says that the body REGULATES the various species of Vitamin D and products derived from it that the body requires. It's difficult to regulate something if there isn't any (or not enough) there in the first place.
My wife had been pushing me to get my Vit. D level checked (her oncologist is requiring her to keep her blood level at around 90 pg/ml), so I had a blood test done. It showed a blood D level of 32 pg/ml. And this was WITH taking 1400 IU per day of Vitamn D3. So I added another 1000 IU.
My wife had been pushing me to get my Vit. D level checked (her oncologist is requiring her to keep her blood level at around 90 pg/ml), so I had a blood test done. It showed a blood D level of 32 pg/ml. And this was WITH taking 1400 IU per day of Vitamin D3. So I added another 1000 IU.
Please consider more closely Marshall's suggestions to measure both the 25D and 1,25D levels. Likely you are only measuring the 25D levels, as it is easier to measure. The 25D is a precursor, and the 1,25D the active form. If the 1,25D level gets too high, then that suggests that the liver has lost control of 1,25D levels, and you have entered, by this work (which you discredit, I realize) the arena where Vitamin D supplementation is harmful, not helpful.