What is vitamin D? What is vitamin D good for? Vitamin D has long been known for supporting normal bone development and muscle strength, and for helping to promote overall bone health. The most conclusive information about the benefits of vitamin D and normal vitamin D levels comes from evidence in bone and teeth development. Vitamin D helps the body use calcium and phosphorus to build and maintain strong bones and teeth. It helps our bodies absorb calcium and phosphorus from the food that we eat. So vitamin D works hand in hand with other nutrients to help promote bone health, and is essential for calcium uptake.