It iis because of the calcium. Your bones dont even "set" properly until you reach 25! ..But calcium needs vitamin D to absorb and be any good to you. There are milks on the market that have proportionate quantities of vitamin D included. If you're trying to get good dense bone though, remember that vitamin C also plays a big part in not only thaat, but in building strength in your muscles. When you lift, it's the vitamin C that bonds with the calcium to cause the contraction in the muscle that allows you to do it. When you bare weight, or put weight on your bones and joints, they become strong.
Blooming Lotus