Deficiency, calcium

A low level of calcium in the blood (hypocalcemia) makes the nervous system highly irritable and causes tetany (spasms of the hands and feet, muscle cramps, abdominal cramps, overly active reflexes, etc.). Chronic calcium deficiency contributes to poor mineralization of bones, soft bones (osteomalacia) and osteoporosis; and in children, chronic calcium deficiency causes rickets and impaired growth. Calcium in the body is found mainly in the hard part of bones. Bones serve as a storage area for calcium. Calcium is added to bones by cells called osteoblasts. It is removed from bones by cells called osteoclasts. Calcium is not just essential for healthy bones. It is also important for muscle contraction, heart action, nervous system maintenance, vitamin B-12 absorption and normal blood clotting. Food sources of calcium include dairy foods, some leafy green vegetables such as broccoli and collards, canned salmon, clams, oysters, calcium-fortified foods, and tofu. Milk packs a fairly high dose of calcium: 300 milligrams in an eight-ounce glass. When children consume calcium, they absorb 75% of it into their bones. By the age of 20, this absorption drops to 30 to 50% and calcium is no longer used to build but to maintain bone density, to replace the calcium lost as the bones constantly remodel themselves. According to the National Academy of Sciences, adequate intake of calcium is 1,200 milligrams a day (four glasses of milk) for men and women 51 and older, 1,000 milligrams a day for adults 19 through 50, and 1,300 milligrams a day for children 9 through 18. The upper limit for calcium intake is 2.5 grams daily.