Calcium - is the most abundant, essential mineral in the human body and is needed to for bones and teeth and is also required for blood clotting, transmission of nerve cell signals, and muscle contraction. Calcium is also important in preventing osteoporosis. Osteoporosis, osteomalacia and rickets are all symptoms of Calcium and/or Vitamin D deficiency. Calcium is found in dairy products, salmon, green leafy vegetables and tofu, but most people eat below the recommended amount of calcium and should consider a supplement.