Severe calcium deficiency in adults will lead to hypocalcemia, which can have very serious symptoms that can manifest as abnormalities in the muscles and nervous system. For example, increased excitability of nerves and muscles, including abnormal sensation in the limbs, mouth and lips, numbness in the limbs, and in severe cases, twitching of the hands and feet, and abdominal pain. When calcium deficiency in adults is severe, it can also lead to heart disease, such as tachycardia, arrhythmia and other symptoms. Calcium deficiency can also cause mental abnormalities and even lead to hypocalcemia crisis, including convulsions, respiratory and cardiac arrest, and other particularly serious clinical symptoms.