Magnesium is an essential mineral found in almost all human tissues, especially bone. Magnesium has two physiological (muscle) and biochemical (nerve) functions in the body. Potassium and sodium are also involved in many of these functions. Magnesium is required for the activation of many enzymes (for example, enzymes involved in DNA replication and RNA synthesis) and the secretion of parathyroid hormone, which is involved in bone metabolism. Its deficiency is manifested by progressive muscle weakness and neuromuscular dysfunction. Vegetables, nuts, bread, fish, chocolate, meat and dairy products contain magnesium.