D2 is from a vegetable source and needs to be converted to D3. D3 is better as it is far more available to the body immediately as it doesn’t need to be converted. D2 is generally considered inferior, which is why it’s scarce. Apparently, it’s the preferred for for die hard vegans.
Sunlight is the best source. Diet is next, then supplements.
“Sunlight is the best source.”
Conversion of sunlight to D3 in the skin is poor in the elderly.