Moreover excess of UVB rays also transform previtamin [D.sub.3] into biologically inactive metabolites, tachysterol and lumisterol
. On the other hand, the other precursor vitamin [D.sub.2] is plant derived and its source is through diet.
However, prolonged exposure to sunlight does not produce toxic amounts of vitamin [D.sub.3] because of the pre-[D.sub.3] conversion to the biologically inactive compounds called lumisterol
and tachysterol .
Vitamin D1, molecular compound of ergocalciferol with lumisterol
. Vitamin D2, ergocalciferol (made from ergosterol).