We've all heard of studies that concluded that vitamin D provided no benefits to patients during the study. Well, maybe this is the reason. It seems that researchers sometimes leave their brains at the entrance to the lab when they are designing research studies. They tend to do things in the easiest way that will yield them the results they want. But that doesn't necessarily lead to accurate and reliable results. The body was designed to produce vitamin D in the skin, whenever sun exposure is available, and this process works very well. It amounts to relatively small to moderate doses of vitamin D on a regular basis. So why would most research projects claiming to study vitamin D choose to use weekly or monthly doses? Probably because it's easier, even though it totally disregards normal dosing patterns.
A recent study seems to reveal why those "bolus dosing" studies are invalid.
The reason may be that the current vitamin D canon (accepted belief) is incorrect. Current canon is the autocrine theory, which states that all of the relevant parent compound (vitamin D) is transported to the liver where it is metabolized to 25(OH)D, and this 25(OH)D is then transported by vitamin D binding protein (VDBP) to the 33 tissues that utilize vitamin D. The cells in these tissues then absorb 25(OH)D through the cell walls where it is again metabolized to form the steroid hormone calcitriol, which regulates genes.
However, this may be not be accurate, as 25(OH)D is strongly bound to vitamin D binding protein (VDBP), and not much of it is free to passively diffuse across cell walls. The 25(OH)D/VDBP complex can be transported across cell membranes by specialized transporter proteins, but to date, these transporter proteins have not been found in very many tissues.
Hollis and Wagner theory states that it’s the parent compound (vitamin D) that diffuses across cell walls. Very little vitamin D is bound to VDBP, so it is free to cross the cell membranes in large amounts by passive diffusion where it is metabolized into calcitriol. This would explain why the parent compound, vitamin D, disappears from the blood so quickly (12-24 hours); it is absorbed into cells.
Why is daily dosing of vitamin D important?If Hollis and Wagner are correct, it explains why so many bolus dosing studies using weekly, monthly or longer doses are negative. When using those doses, even large amounts of vitamin D would be cleared from the systemic circulation in several days and thus not be available to diffuse into cells and work vitamin D’s magic.
Proof once again that many medical researchers either don't know what they're doing, or they are out to intentionally distort the results of their studies.
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