Vitamin D is a fat-soluble vitamin that the body uses to promote calcium absorption and bone growth.
What happens if you do not get enough of it
A human that does not get enough vitamin D will most likely end up with bones that are thin, brittle, or misshapen.
Very little food has vitamin D in it. The main foods are: fish, fortified orange juice, eggs, and dairy products. Many humans take supplements and almost every human gains some of their needed daily intake by the Ultraviolet light emitted by the sun.
"Vitamin D." Office Of Dietary Supplements. Office Of Dietary Supplements, National Institutes of Health, n.d. Web. 04 Nov. 2013. <http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/>.