Vitamin D prevents the children's bone disease rickets.

VOA: special.2009.04.21

Vitamin D is essential for bone and muscle health in both adults and children.

CNN: How much vitamin D do I need?

Cliff Rosen, past president of the American Society for Bone and Mineral Research, agreed that there isn't much data showing calcium-and-vitamin-D supplements can prevent bone fractures.

WSJ: Vitamin D and Calcium Supplements May Not Stop Fractures

And of course vitamin D is key to building bone health and preventing osteoporosis.

FORBES: That Vitamin D You're Taking? It May Not Be What It Appears