For years, many people have taken calcium and vitamin D supplements to help keep their bones strong as they age. Walk into any pharmacy or supermarket, and you'll find shelves full of products promising to support bone health, prevent fractures and reduce the risk of falls. Calcium is an important building block of bone, while vitamin D helps the body absorb calcium. If weak bones increase the risk of fractures, surely taking more calcium and vitamin D should help keep bones strong. But a major