ABSTRACT
One of the great scientists Sir Lord Kelvin said: “When you can measure what you are speaking about and express it in numbers, you know something about it, and when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind.” This statement somehow makes sense for vitamin D. The discovery and elucidation of the understanding of the physiological mechanism of vitamin D is linked to the history of analytical chemistry, and it explains why it took 50 years to discover the active vitamin D metabolite and why we still have much to learn about vitamin D.
