This article provides important information regarding just how crucial Vitamin D is for bone health. It helps your body keep a good balance of calcium and phosphate in the blood. With low vitamin D levels, children can develop rickets and adults can develop osteomalacia, a condition in which weak bones cause bone pain, fractures, and muscle weakness. Vitamin D also has many other functions in the body. It helps control the growth of your cells, improves your immunity, provides nerve and muscle strength, and reduces disease-causing inflammation in your body.