We carry almost 1 kg (= 2+ pounds) of calcium in the bones, but the concentration
of calcium
in the blood is very low (approx. 10
mg pr dl.) and even an increase to 15 mg/dl would cause very serious symptoms. If needed, calcium can be released from the bones, so the amount of calcium in the blood is fairly constant. If we go for years and decades with insufficient calcium intake, the bones can get weakened as they are drained for calcium. This is known as osteoporosis.