Calcium Deficiency

Calcium deficiency describes two different problems that are easy to confuse. The first is a low calcium intake. About 98% of the body's calcium is stored in bone, and when the diet falls short the body keeps blood calcium normal by drawing on that reserve. Low intake therefore usually causes no symptoms for years, and a normal blood calcium result does not rule it out; the cost shows up later as thinner bone, osteoporosis and, in children, rickets. The second is hypocalcemia, a low level of calcium in the blood itself (below about 8.5 mg/dL, or 2.12 mmol/L). That one does cause symptoms, and it is usually a hormone problem rather than a diet problem. Hypocalcemia is most often caused by vitamin D deficiency, low magnesium, or underactive parathyroid glands. In hospital the most common cause of sudden, symptomatic hypocalcemia is parathyroid damage during total thyroidectomy; in primary care the most common cause is vitamin D deficiency. Kidney disease, critical illness and some medicines (bisphosphonates, cisplatin, proton pump inhibitors, and anti-seizure drugs that speed up vitamin D breakdown) can also cause it. When calcium falls slowly there may be no symptoms at all; a rapid fall brings tingling around the mouth and in the fingers, muscle cramps and spasms, and in severe cases seizures and heart rhythm problems. Low intake is widespread in the US and worldwide: average national intakes range from 175 to 1,233 mg a day, and many Asian countries average under 500 mg. The payoff from raising intake in adults is smaller than often claimed: in people over 50, extra calcium raised bone density by only about 0.6-1.8%, and a 2026 meta-analysis (11 calcium-only trials, about 9,000 people) found little to no reduction in fractures from calcium supplements. The clearest benefit is in children with very low intakes, where small trials found calcium healed nutritional rickets better than vitamin D alone; most rickets, though, is due to vitamin D deficiency.

• •Tingling around the mouth
• •Pins and needles in hands and feet
• •Muscle cramps, twitching and spasms
• •Hand and foot spasms (carpopedal spasm)
• •Depression or other mood changes
• •Dry skin and brittle nails (long-standing)
• •Cataracts (long-standing)
• •Seizures or abnormal heart rhythm (severe)

• •Low calcium intake over years
• •Vitamin D deficiency
• •Low magnesium
• •Parathyroid damage after neck surgery
• •Autoimmune hypoparathyroidism
• •Chronic kidney disease
• •Malabsorption such as coeliac disease
• •Bisphosphonates, cisplatin or proton pump inhibitors
• •Some anti-seizure medicines (lower vitamin D)
• •Pancreatitis, rhabdomyolysis or large blood transfusions

Low dietary intake is the main cause of a long-term calcium shortfall: diets with little dairy or fortified food, lactose intolerance or milk allergy, vegan eating, and the higher needs of adolescence and of women after menopause, when falling estrogen reduces calcium absorption and increases loss from bone. Low blood calcium (hypocalcemia) has different roots: too little parathyroid hormone (most often after thyroid or parathyroid surgery, sometimes autoimmune), vitamin D deficiency or malabsorption (for example coeliac disease), magnesium deficiency, chronic kidney disease, and medicines such as bisphosphonates, cisplatin, proton pump inhibitors and some anti-seizure drugs. The two overlap through vitamin D, which the gut needs to absorb calcium: the lower someone's vitamin D, the more calcium they need to avoid rickets and osteomalacia.