What I know is that those of my relatives and acquaintances who rely on D-3 and sunshine, none have got flu or colds. Among those who get flu shots, a majority get some virus each year, some multiple in years of low effectiveness and bad guesses and a couple have become ill within three days after getting the shot. I don’t take the government’s word for much of anything any more. I research stuff that applies to me and mine.
You can prove just about anything to yourself anecdotally, but don’t expect others to do so. If your technique works, great. I like both vitamin D3 and vaccinations, and hopefully that technique will work for me and mine.