The most serious complications of vitamin D deficiency are low blood calcium (hypocalcemia), low blood phosphate (hypophosphatemia), rickets (softening of the bones during childhood), and osteomalacia (softening of the bones in adults). However, these complications have become less common over time because many foods and drinks have added vitamin D.

“Subclinical” vitamin D deficiency or vitamin D insufficiency is common, and is defined as a lower than normal vitamin D level that has no visible signs or symptoms. However, vitamin D insufficiency is associated with reduced bone density (osteopenia or osteoporosis), a mild decrease of the blood calcium level, elevated parathyroid hormone (which accelerates bone resorption), an increased risk of falls, and possibly fractures, all of which can seriously affect a person’s quality of life.

Thus, identifying and treating vitamin D insufficiency or deficiency is important to maintain bone strength. Treatment may even improve the health of other body systems, such as the immune, muscular, and cardiovascular systems, although more research is needed in these areas.