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. In the body it functions as a coenzyme in the form of thiamine pyrophosphate and is important in carbohydrate intermediary metabolism. The symptoms of thiamine deficiency are known as beriberi, a syndrome consisting primarily of peripheral neuritis marked by sensory and motor paralysis of the limbs and, finally, heart failure. People of Asia who acquired beriberi as a result of a diet of mainly polished rice could be cured by adding rice polishings, which are high in thiamine. Today, thiamine deficiency results from liver damage and most often occurs in nutritionally deficient alcoholics.