The mineral calcium plays a number of important roles in the body, including maintenance of bone structure, blood clotting, and muscle and nerve functioning. Public interest in optimal calcium intake has grown in response to research reports concerning osteoporosis, a disease that reduces bone density and strength, putting patients at risk for multiple fractures and skeletal deformities. Osteoporosis, which causes mild to severe disability in 15 to 20 million Americans, may be preventable if calcium intake is sufficient. Most foods rich in calcium are from the dairy category, with milk and milk products being the best sources. Several other foods, including greens, canned fish with bones, and tofu, provide substantial amounts of calcium. The authors investigated a claim that addition of vinegar to soup stock draws large amounts of calcium out of the bones being cooked. Several reports stated that one to two cups of this soup stock contained as much calcium as a quart of milk. In the experiment, different stocks were prepared from water and chicken bones; some had no vinegar added while other stocks had white vinegar added. The stocks with and without vinegar did not differ in calcium content and all were poor sources of calcium, providing from 6 to 11 mg of calcium per cup. The Recommended Dietary Allowance (RDA) for adults is 800 mg calcium per day. In contrast to the soup stock, one quart (four cups) of skim milk provides 1,184 mg calcium. The authors conclude that no individual should rely on vinegar-based soup stock as an important source of dietary calcium.