Cheese can make a valuable contribution to our diet, supplying generous amounts of protein, vitamin A and calcium, which helps prevent osteoporosis. It also contains vitamins B2, B12 and D, niacin and folic acid, as well as phosphorus and zinc. It is beneficial to children, because calcium aids the growth of strong bones and teeth, and also to the elderly, because it provides a concentration of nutrients that might otherwise be lacking in their diet. The vitamin B12 is especially welcome for vegetarians, who may like to seek out types made with a vegetarian rennet substitute rather than traditional rennet - a substance extracted from the stomach lining of calves to clot the milk.