a low blood calcium (hypocalcaemia). Hypocalcaemia makes the nervous system highly irritable with 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, rickets and impaired growth. 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. According to the national academy of sciences, adequate intake of calcium is 1 gram daily for both men and women. The upper limit for calcium intake is 2.5 grams daily.