Most bone mass accumulates during childhood and adolescence. About 90% of an adult's ultimate bone mass is accumulated by the end of the adolescent growth spurt around age 17. Increasing bone mass deposition during the first two decades of life reduces the risk of later bone fractures.

According to government research, more than one-half of all children, and more than 85% of girls age 12-19, do not meet the 1989 Recommended Dietary Allowance (RDA) for calcium. Teen girls in the United States average only about 740 mg of calcium per day, well below the amount needed for normal growth and development.

Calcium requirements for children 4 through 8 years are 800 mg per day; children and adolescents aged 9 through 18 years need 1300 mg per day. Low-fat or fat-free (skim) milk and dairy products are the best sources of calcium. An eight ounce serving of milk (any milk - whole, low fat or skim) contains 300 mg of calcium, as well as vitamins D, A, and B12. It also contains the minerals phosphorus, magnesium, and potassium, essential for bone growth and mineralization, as well as protein and riboflavin. Other good sources of calcium include yogurt, cheese, and calcium-enriched orange juice.

Some foods contain significant amounts of calcium, but this dietary calcium is not used as effectively by the body as that contained in milk and dairy products (that is to say it is not as "bioavailable"). For example, while dark green, leafy vegetables are good sources of calcium, it is not as easily absorbed by the body as the calcium in dairy products (it takes 15 servings of spinach for the body to absorb as much calcium as one glass of milk). This phenomenon of low bioavailability is caused by the presence of certain substances in the plant such as oxalates and phytins which bind calcium in the intestinal contents and prevent its absorption into the bloodstream.

Vitamin D is essential for calcium absorption and utilization in the body, and it should be provided for all children. Milk consumed by children should always be vitamin D fortified. Exclusively breast fed infants, especially dark skinned breast fed infants, should have routine vitamin D supplementation in the form of vitamin drops.

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