Contrary to popular belief, our framework of bones isnt a rigid and unchanging structure.

Each year, our bodies replace about 20 percent of our bones tissue, which means that our activities at every age influence their health. Sections of old bone break down, creating gaps to be filled by new bone. Until about age 30, we build bone very efficiently, so making the right health moves, such as exercising and getting enough calcium, helps your bony framework reach its genetically determined peak strength. Think of your bones as a retirement fund: The more you deposit when you re young, the better off you will be in later years, when you need to draw on your reserves. The problem is that kids prefer soda to a glass of milk: they are coming up short of the calcium and vitamin D they need to build up good health. Many of them also lead an inactive life, so they arent getting the bone-building benefits of regular exercise either. That s a problem every parent should be concerned about.