10 minutes outside in summer? Does that address our alledged reduced ability to make vitamin D with age? Does it address that vitamin D is made from cholesterol and lots of people are on an anti-cholesterol crusade? Does it address that UVA hinders the reaction which UVB encourages, and therefore sitting in the sun behind glass might undo some of the benefit? (hint: no).

Does the daily recommended amount for supplementation address which kinds of Vitamin D are useful and which aren't? Which kinds are more easily absorbed? That different people absorb different amounts? That it's possible to overdose? (hint: no).

These skirt around the real point which is to raise some particular blood level of a specific kind of Vitamin D. If you aren't getting that, specifically, measured then whatever else you do in terms of sunlight or supplementation is winging it and hoping for the best (and risking overdose) or merely assuaging some guilt that you should be healthier by doing "something".