Does human behavior determine vitamin D levels?
The pharmacology contained in this paragraph may be a bit confusing to some, but it is vitally important in understanding vitamin D. It is so important that Professor Reinhold Vieth, of the University of Toronto, wrote an entire chapter about its implications in the most current textbook of vitamin D. Unlike any other steroid hormone, substrate (precursor) concentrations are absolutely rate-limiting for activated vitamin D production. The enzyme that first metabolizes vitamin D in the liver and the enzyme in tissue where activated vitamin D is made both operate below their respective Michaelis-Menten constants throughout the full range of their normal substrate concentrations, i.e. the reactions follow first-order, mass-action, kinetics. In English, this means the more vitamin D made in the skin or taken by mouth, the more vitamin D in your blood, and the more vitamin D in your blood, the more activated vitamin D in your brain. That is, levels of activated vitamin D during brain develo