According to LifeZette, taking calcium supplements to prevent bone loss might be dangerous:
Your calcium supplement isn’t doing you any favors. After 10 years of medical research that employed more than 2,700 people, researchers at Johns Hopkins University have determined that calcium supplements actually increase the risk of heart attack.
Researchers began feeling skeptical about the health benefits of the supplements after they realized the calcium wasn’t making it to the bones — and it wasn’t passing through the body, either. Instead, the supplements deposited calcium into the soft tissue of the body, such as the muscles and blood vessels.