Earlier quoted context omitted.
This is the issue raised by comments like the one above. We understand that evidence based medicine handles statistical averages very well. But if you fall out of that, all you're left with is snake oil salesmen. There's a need for an intermediate layer of evidence yet "taylored" (and not kidney-costing if possible).
Ya, but I think most good doctors operate with a balance of probabilities framework. Yah, there may not be conclusive evidence showing it’s widely effective, but based on this case, it’s obvious the person isn’t getting enough sunlight, and they communicated that to the doctor, and so why not do a trial of something like vitamin d? It’s widely studied, has very few serious downsides, and is cheap.
Can we get to the specifics? How would you propose the doctor do it? Let's say the doctor prescribes a certain dosage per day. How will the doctor know it is helping this particular patient? How long should the trial continue before he sees results?
Most studies showing Vitamin D benefits are very long term (unless it is bone related).