I think you may be thinking of Vitamin B12 which is the vitamin that has no plant sources. Vitamin D deficiency is very very common now that people spend so much time indoors and wear sunscreen. Sunlight is the biggest/fastest source of Vitamin D (especially this time of year). I've been supplementing with 1-2000 units daily for several years (low by the standards on this board) and have raised my levels from 40 something to 70 something.

Vitamin D is actually a hormone, not sure why it is called a vitamin.