Calcium is best known for building strong bones, but its role extends far beyond the skeleton. It is essential for muscle contraction, nerve signaling, hormone release, blood clotting, heart rhythm, and cellular communication. Because calcium is so critical, the body tightly regulates its levels through the parathyroid glands, kidneys, bones, and vitamin D. When calcium becomes too high or too low, the effects can be widespread, sometimes subtle, and sometimes life threatening.
Low calcium makes the nerves and muscles more sensitive, which can lead to tingling around the lips or fingers, muscle cramps, twitching, and spasms in the hands and feet. Some people may experience carpopedal spasms (hand and finger tightening), facial twitching known as Chvostek sign, or prolonged muscle contraction called Trousseau sign. They may also feel tired, weak, or mentally foggy. In more severe cases, low calcium can cause difficulty breathing, seizures, or abnormal heart rhythms.
Low calcium may be caused by low vitamin D, problems with the thyroid or parathyroid glands, kidney disease, or low magnesium levels. Because some calcium in the blood is attached to a protein called albumin, a lab result may appear low even when the active calcium is normal, so doctors may repeat, adjust, or check ionized calcium levels for accuracy.
High Calcium slows down muscles and nerves and puts strain on the kidneys and heart. People with high calcium may feel tired, weak, constipated, very thirsty, or notice they are urinating more often. It may also cause nausea, stomach discomfort, bone pain, mood changes, confusion, or dehydration, and if levels become extremely high, it can lead to kidney stones, dangerous heart rhythm changes, or drowsiness progressing to coma.
The most common causes include an overactive parathyroid gland, certain cancers, too much vitamin D, or some medications. High calcium requires medical evaluation because treating the underlying cause can protect the kidneys, support heart and nerve function, improve energy and mood, and prevent serious complications.
Since both high and low calcium levels can affect the brain, heart, muscles, and kidneys, recognizing symptoms early and getting tested is important for maintaining overall health.