Calcium is essential for strong bones and teeth, and it's also necessary for your nerves to function and your muscles to contract and relax properly. You get that calcium from the foods you eat. While there are many non-dairy foods that are rich in calcium, dairy is such an excellent source of calcium that it qualifies as a food group. According to the United States Department of Agriculture, you need about three servings of dairy every day. The downside of dairy is that it can be high in saturated fat.