Calcium deficiency; hypocalcemia
Hypocalcaemia is a low level of calcium in the blood. In health, various hormones keep the blood calcium levels within a narrow range, but changes in the level of these hormones or, rarely, reduced consumption of calcium in the diet can lead to the calcium level dropping too low.
Calcium is found in many foods especially dairy products and milk, and most diets contain sufficient quantities of calcium. The major store of calcium in the body is within the bones, but it is found to some extent in most parts of the body. Vitamin D is required to absorb calcium from the gut into the bloodstream. Vitamin D is mostly produced in the skin in response to sunlight and is also absorbed from food eaten as part of a healthy balanced diet. The liver and kidneys convert vitamin D (produced in the skin and taken up in the diet), into the active hormone. Active vitamin D helps to increase the amount of calcium the gut can absorb from eaten food that maintains healthy levels of calcium in the blood. The parathyroid glands sense the amount of calcium in the blood and produce increased amounts of parathyroid hormone if the calcium level drops. This hormone helps to reduce the loss of calcium in the urine and releases some calcium from the bones. These two hormones work together to ensure that blood levels of calcium are maintained within the normal range.
There are several possible causes of hypocalcaemia, including:
Many people with hypocalcaemia will have no symptoms at all, especially if they have had the condition for some time. Most people who do have symptoms will note tingling around the mouth and pins and needles or numbness in the hands. Muscle stiffness and cramps commonly occur, whilst confusion, difficulties in breathing, heart problems and locking of muscles in a fixed position (tetany) occur only when the calcium level is very low.
Mild hypocalcaemia is very common and is rarely associated with symptoms. Because of dietary effects on calcium and vitamin D levels, it particularly affects people with poor or restricted diets, people with lack of exposure to sunlight, e.g. those who wear clothes that cover most of the skin or those who stay indoors a lot, such as elderly people in care homes. More severe hypocalcaemia is much rarer.
Most cases of hypocalcaemia are not inherited, although some people with autoimmune parathyroid problems will have a family history of autoimmune problems affecting other endocrine glands (e.g. multiple endocrine neoplasia disorders). 'Resistance to parathyroid hormone' is a group of rare disorders where either the kidney, the bone or both do not recognise and respond to parathyroid hormone normally, and hypocalcaemia results. Depending on the features of the disorder, this can be passed on by either the mother or the father.
Calcium levels (along with vitamin D and parathyroid hormone levels) can be checked on a simple non-fasting blood sample, which can be carried out as an outpatient. Depending on the results, further tests may need to be carried out to establish the underlying cause of the hypocalcaemia.
Treatment of hypocalcaemia depends on the cause. Vitamin D can be given in tablet or injection form, if required, and this is often given with calcium supplements. If the cause of the hypocalcaemia is hypoparathyroidism, patients will also receive treatment for this condition. If a person has severe symptoms of hypocalcaemia, it may be necessary to give intravenous calcium in hospital to control severe symptoms.
Most people do not have side-effects to treatment. Occasionally people taking calcium supplementation complain of a chalky taste in the mouth and constipation; higher doses (more than 1,500mg a day) can sometimes lead to stomach pain and diarrhoea. It is very rare for vitamin D treatment to cause raised levels of blood calcium above the normal range.
If a dietary or lifestyle explanation can be found for either low calcium or low vitamin D, it is sometimes possible to address this and patients make a full recovery. Persistent untreated hypocalcaemia has a tendency to cause build-ups of calcium and phosphate in parts of the body, including the brain, but this is rare. The doctor may also want to check for other associated conditions at regular intervals if the hypocalcaemia is the result of an autoimmune disease.
Last reviewed: Feb 2018