Those who suffer from myositis, or other conditions that lead to inflammation in their muscles, are likely to also be diagnosed with a deficiency of vitamin D. Vitamin D is essential for proper muscle functioning as it supports the body’s ability to absorb calcium and phosphorus into the bones. Low levels of vitamin D result in an increased risk of fractures in the bones, as well as pain and weakness in the muscles. A severe vitamin D deficiency will also increase older adults’ risk of falling and being severely injured. A severe vitamin D deficiency alone can lead to various types of bone disease.