BTW, I take 4,000 IU of vitamin 'D' a Day. I haven't been sick once in three years.
I've seen some of yours as well. I think what clinched it for me was what's on the NIH website. According to what's there, at my latitude, I can't make any vitamin D from sunlight for about a third of the year. That should mean, as a practical matter, that I'll make virtually none for two thirds of the year. And thinking about it, I probably don't make that much in the best third of the year.