The importance of vitamin D is well known. As far back as the 1930s, doctors first recognized the link between a vitamin D deficiency and the skeletal disease called rickets. Rickets causes a softening of the bones and teeth. Even if someone's diet has adequate levels of calcium, without enough vitamin D to properly control calcium and phosphate levels in the blood stream, demineralization of the bones can take place. The symptoms of rickets include bowed legs, bone pain, dental problems, a widening of the wrists, frequent bone fractures and skull deformities.
Because rickets is seldom seen in first-world countries, it's easy to think that vitamin D deficiencies are a thing of the past. However, new research has recently shed light on other, more subtle, symptoms of a vitamin D deficiency. Many illnesses which, at first glance, seem totally unrelated to something as physically obvious as rickets actually may have their roots in a lack of vitamin D.