Vitamin D is an essential vitamin produced when the body is exposed to sunlight. Food sources include fish, egg yolks, fish liver oils, and fortified dairies and grains. Vitamin D produces healthy bones and helps the body absorb calcium. A vitamin D deficiency can cause a variety of health problems such as osteoporosis, asthma, cancer, and rickets, a childhood disease that causes soft and brittle bones and skeletal problems. Rickets is a rare condition in the United States but more common in other countries. Some rickets risk factors are inadequate nutrition and little sun exposure. Follow the links below to find WebMD's comprehensive coverage about how rickets or vitamin D deficiency is caused, what it looks like, how to treat it, and much more.