Drink milk and eat yogurt for by far the richest food sources of calcium. Your body needs calcium to contract muscles, expand and contract blood vessels, secrete hormones and enzymes, transmit nerve impulses and strengthen bones and teeth, according to the Office of Dietary Supplements. The body regulates the concentration of calcium in the blood to support these functions. Stored calcium in bones provides a rigid skeletal frame and serves as a calcium reservoir to keep tight control over circulating calcium.
Calcium, the most abundant mineral in the body, helps grow healthy bones early in life and minimize bone loss later in life. From 1 to 2 percent of your body weight is calcium, and 99 percent of it is in bones and teeth, according to Eleanor Whitney and Sharon Rolfes in "Understanding Nutrition." The bones provide a reservoir of calcium for the blood. Blood calcium helps the muscles move, the heart beat and nerves communicate. Hormones and vitamin D regulate the level of calcium in blood.
Choose fat-free or low-fat milk. The most abundant source of calcium is milk and milk products. Most people need at least three servings from the milk group to meet daily calcium recommendations. About 30 percent of calcium from milk products is absorbed, compared with less than 5 percent from spinach. You would need to eat 8 cups of spinach containing six times as much calcium as 1 cup of milk to deliver the same amount of absorbable calcium to your body, according to "Understanding Nutrition."
Choose low-fat and nonfat versions, either plain or flavored. Use yogurt as salad dressing or sandwich spread. Use in dips, desserts and main dishes. Substitute frozen yogurt for ice cream. One cup of nonfat, low-fat or fruit yogurt provides 31 percent to 45 percent of the adequate intake for calcium, according to the Ohio State University Extension. One cup of frozen yogurt provides about 10 percent of the intake for calcium. If you are lactose-intolerant, choose yogurt for a lactose-free, high-calcium food.
The FDA regulates labeling of food products. Products labeled as "high," "rich in" or "excellent" source of calcium supply at least 20 percent of the adequate intake for calcium. A product labeled a "good" source of calcium must provide at least 10 percent. Products labeled "more," "enriched," "fortified" or "added" have 10 percent or less, according to "Understanding Nutrition."
Adults need an adequate intake of 1,000 mg of calcium per day and can safely consume up to 2,500 mg per day. The FDA requires the nutrition labels on food containers to state the percentage of daily value of calcium provided per serving.
A low calcium intake during the growing years limits the optimal mass and density of bones. Most people achieve their peak bone mass by their late 20s. Low calcium intake may lead to less dense bones or bone loss and higher risk of osteoporosis.