Isn't it a possibility that our lifestyles have changed in ways that have reduced the amount of Vitamin D we have historically received? Are we incidentally measuring the sum result of our social choices?
Of course, we get less sun from being outdoors less and wearing more sunscreen. This isn't just a possibility, this is generally understood.
Well, most of us certainly spend much less time outside than common folks in preindustrial societies.
Probably yet I don't see much direct connection. People were not having less heart attacks or heart attacks later in life. I suppose testing a vitamin D theory to significance may not have been easy before ~1980 because of many other causes of heart attack having higher frequency.