http://www.niams.nih.gov/Health_Info/Bone/Bone_Health/Nutrition/calcium_supp.asp
National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health
Getting enough calcium is important because the human body cannot make it. Although food is the best source of calcium, most Americans do not get enough of it from food sources. Calcium-fortified foods (like orange juice, bread, cereals, and many others on your grocer’s shelves) and calcium supplements can fill the gap by ensuring that you meet your daily calcium requirement.