The intake is balanced by losses in urine and feces. The blood levels of calcium and its intestinal absorption, deposition, or mobilization from bone are all controlled by a complex interplay of vitamin D, parathyroid hormone, and calcitonin. Contrary to some long-held beliefs, high intakes of protein and phosphorus do not lead to a loss of calcium. Magnesium is an essential element in human metabolism and functions in the activities of muscles and nerves, protein synthesis, and many other reactions. Magnesium deficiency may occur in alcoholism, diabetes mellitus, pancreatitis, and renal diseases.
Prolonged deficiency can cause changes in heart and skeletal muscle.
Excessive retention of magnesium can occur in renal disease and results in muscle weakness and hypertension. Iron is a vital component of hemoglobin and also of certain respiratory enzymes. Increased requirements for iron occur during the growth period and pregnancy and with excessive menses and other instances of blood loss. The average diet contains 10 to 15 mg a day, adequate for most people. Iron deficiency, resulting in anemia, can be treated by large amounts of iron in order to gain positive absorption.