The dynamic duo of calcium and exercise helps build strong bones and goes a long way toward preventing osteoporosis, a bone-weakening disease that causes bones to break easily.

"People's daily calcium needs vary throughout life. It's especially important for growing children and adolescents, pregnant and nursing women and older adults, notably postmenopausal women, to consume enough calcium to build and maintain strong bones and to support other body activities that require calcium," said Sandra Bastin, Extension food and nutrition specialist with the University of Kentucky College of Agriculture.

"Most adults need 1,200 to 1,500 milligrams of calcium each day," she said. "Four to five servings of calcium-rich foods daily will supply this requirement. Children ages six to 10 years should have 800 to 1,200 milligrams of calcium daily, or three to four servings of calcium-rich foods."

Participating in regular exercise, especially weight-bearing or strength-training activities, is another way to strengthen bones. These activities include baseball, basketball, soccer, tennis, weight lifting, aerobics, dancing and walking. Since these activities are site-specific in that they strengthen only those bones used directly in the exercise, it's a good idea to incorporate a variety of weight-bearing activities into the exercise program.

Good nutrition, including the recommended daily amount of calcium, can reduce the likelihood of osteoporosis up to 50 percent. If the body doesn't receive enough calcium, it will gradually deplete needed calcium from the bones. This depletion weakens bone, causing

them to break more easily. Calcium helps your heart to beat, muscles to contract and blood to

clot. It can reduce the risk of chronic health problems and diseases.

Bastin said food sources of dietary calcium include milk, cheeses, yogurt, dark green leafy vegetables, legumes and canned sardines or salmon with bones. Other sources are calcium-fortified foods like orange juice, breads, cereals, breakfast bars and soybean products such as soy milk or tofu. One cup of milk, yogurt or calcium-fortified juice counts as one calcium-rich serving. One cup of kale or broccoli, three ounces of canned salmon, or one ounce of calcium-fortified cereal provides one-half calcium-rich serving.

To reduce fat and calories in dairy products, choose reduced-fat, low-fat or no-fat foods.

People with lactose intolerance have trouble digesting the main sugar in milk. However, they still can obtain calcium from food sources such as lactose-free milk, yogurt and hard cheeses, which are low in this sugar. Other foods that contain calcium are leafy green vegetables, legumes and calcium-fortified foods.

When grocery shopping, read nutritional information on labels to help you select foods containing the greatest amount of vitamins and minerals for the number of calories. For example, look for foods with 10 percent or more of the daily value (DV) for calcium.

"Ideally, you should satisfy daily calcium needs by incorporating good sources of calcium into a well-balanced diet based on a variety of foods, rather than taking a calcium supplement," Bastin said. "This is because eating a variety of foods provides essential vitamins and nutrients that wouldn't be available in a supplement alone.

"People who decide to take calcium supplements should avoid those made from bone meal or dolomite because they might be contaminated with lead, mercury or arsenic."

For the most benefit from a calcium supplement, take it in small doses -- no more than 600 milligrams of available calcium -- because the body absorbs small doses best. If you are

you're not taking a multiple vitamin, use a calcium supplement that provides 200 to 400 International Units of Vitamin D. This vitamin helps the body absorb and use calcium.