The highs and lows of calcium

Dr Angela Murphy explains the symptoms and the treatment for both low and high levels of calcium.

What is calcium?

It’s is a mineral necessary for the healthy functioning of bones and teeth. In addition, it’s necessary for normal blood clotting, muscle contraction, nerve function and heart rhythms. Most calcium in the body is stored in bone with only 1% found in blood, muscles, and other tissues.

The body gets calcium from eating foods rich in calcium, particularly dairy products, nuts and seeds and certain vegetables, such as kale. If the diet is low in calcium, then the body will start to extract calcium from bone which can cause bone disorders, such as osteoporosis.

Recommended daily requirements

The table below lists the recommended daily requirements for different age groups.

How are calcium levels affected?

Levels of calcium are controlled by the parathyroid glands, which as the name suggests, lie next to the thyroid gland in the neck. These four, small glands secrete parathyroid hormone (PTH) which acts in several places in the body:

1. Gut – to stimulate uptake of calcium from food by activating vitamin D.
2. Kidneys – to slow down the loss of calcium in the urine.
3. Bone – to stimulate release of calcium from bone into the circulation.

The system should be balanced enough to keep enough calcium available to all the cells in the body, but not remove too much from the bones. When calcium levels are too high or too low, we always look to see what the PTH level is first and from there can decide the cause of the imbalance.

Hypercalcaemia (high blood calcium)

The most common causes are:

• Primary hyperparathyroidism – This usually occurs sporadically, although sometimes there is a family history. In most cases, one of the four parathyroid glands have an adenoma which overproduces PTH. Sometimes the entire gland is enlarged, and this is called hyperplasia. Rarely more than one gland will be overactive. It’s rare for cancer to be a cause.
• Malignancy – Some cancers produce a PTH-like hormone which then increases calcium levels in the blood. Other cancers cause direct damage to bone which releases too much calcium.
• Hormonal disorders –  Such as an overactive thyroid gland or adrenal gland disorders.
• Medications – Can also increase calcium levels. For example: lithium, certain water tablets and excess use of vitamin A and D.

There are less common conditions, such as prolonged illness in ICU, hereditary disorders and inflammatory conditions, which can also cause hypercalcaemia.

Symptoms

A traditional mnemonic categorises the main symptoms of hypercalcaemia: bones, stones, abdominal groans, and psychic moans. This summarises the main clinical features of high calcium levels:

• Bone loss resulting in diseases, such as osteomalacia and a type of osteoporosis;
• Kidney stones and decrease in kidney function;
• Constipation and other gastrointestinal complaints;
• Mood disorders, such as depression, and a general feeling of being unwell.

Treatment

Naturally, this depends on the cause as well as the actual level of calcium. If the levels are very high, the first step is to lower it with medication and intravenous fluids. The definitive treatment for primary hyperparathyroidism is to surgically remove the overactive parathyroid gland. This is a safe procedure in experienced hands with excellent results.

Hypocalcaemia (low blood calcium)

The most common causes are:

• Hypoparathyroidism – Again this can occur sporadically but more commonly as a result of surgical removal of the parathyroid glands, radiation to the neck or a disease process that infiltrates the parathyroid glands.
• Resistance to the action of PTH – This can occur in kidney disease and with certain drugs as well as a condition on its own called pseudohypoparathyroidism. This means that although the PTH level is normal, the body is resistant to its action and behaves as if there is no PTH to keep calcium levels stable.
• Vitamin D deficiency.
• Resistance to the action of vitamin D – This is a rare hereditary condition.

There are other illnesses which can cause a sudden drop in calcium levels, such as acute pancreatitis, but when treated the levels can normalise.

Symptoms

The classic symptom of hypocalcaemia is tetany. This is spontaneous muscle contractions resulting in spasm, especially of the hands or feet. There may also be a tingling sensation around the mouth and in the fingers. If the levels drop too low this may cause seizures. Chronic low calcium levels in children will affect growth and development.

Treatment

If levels are very low and especially if they have dropped suddenly, it might be necessary to give intravenous calcium. The goal of therapy is to maintain levels in the normal range, and to get to the correct dose of supplements may take some time.

It will usually be necessary to have vitamin D supplementation as part of the treatment. An average dose of calcium supplementation for hypocalcaemia is 1.5 – 3g daily. Long-acting vitamin D2 can be given weekly in many cases. Sometimes a shorter-acting vitamin D, such as calcitriol, needs to be used. If there is difficulty restoring levels to normal, you should be referred to a specialist.

Conclusion

For people living below the poverty line, dietary calcium deficiency can occur. Fortification of foodstuffs has helped to lower this risk. For example, a 100g of Pronutro porridge has 530mg of calcium.

Generally, low calcium due to poor absorption or dietary deficiency can be easily corrected. There is no benefit to taking supplements if you have normal calcium levels. High calcium levels must always be investigated and then the cause can be treated.

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