Doctors have recently found that the majority of those who live in cool climates - whether omnivore, vegetarian or vegan - are vitamin D deficient. All this is in spite of the fact that some fish contain vitamin D and milk, cheese and ice cream are fortified with Vitamin D for those who follow an omnivore or vegetarian diet. For vegans rules are the same. People who do not get adequate sun exposure or Vitamin D fortified foods are at the risk of developing Vitamin D deficiency unless they supplement. Vitamin D deficiency classically causes rickets and osteomalacia (thin bones) and is more common in children who are vitamin D deficient. Prolonged breastfeeding is a cause of rickets in some children who don't get enough vitamin D in their breast milk. Excessive use of sunscreens can cause vitamin D deficiency. In adults, vitamin D deficiency can cause bone weakness and bone pain. Those who are especially encouraged to supplement with vegan vitamin D include those greater than age 50.