Abstract
Osteosarcopenia is a condition of combined osteoporosis and sarcopenia, both of which are associated with aging. Osteoporosis, sarcopenia, and osteosarcopenia are all highly prevalent globally in aging populations. Vitamin D has been associated with a variety of health conditions, including musculoskeletal health, heart disease, cancer, autoimmune disease, and infectious disease. It is therefore a potential contributing factor to the risk of osteosarcopenia. Like osteosarcopenia, vitamin D deficiency is highly prevalent globally in older people. If vitamin D deficiency contributes to the development of osteoporosis, sarcopenia, and osteosarcopenia then it will be important to address vitamin D deficiency and concurrent high parathyroid concentrations. This chapter will discuss how vitamin D and parathyroid hormone affect bone and muscle health. It will also discuss research assessing the impact of vitamin D deficiency on osteoporosis and sarcopenia as separate entities, as well as newer research assessing the impact of vitamin D deficiency on osteosarcopenia specifically.