Who should not take Calcium

Calcium is sold over the counter, and so it is often perceived as a supplement "for everyone." In reality there is a whole range of conditions in which extra calcium can be dangerous or requires caution and medical supervision. The editorial team has systematized the absolute and relative contraindications, as well as the situations in which a consultation is needed before starting.

Absolute contraindications

An absolute contraindication is a situation in which taking a calcium supplement is in principle not allowed without a special medical decision. For calcium this is primarily hypercalcemia — an elevated level of calcium in the blood from any cause.

Hypercalcemia is itself a symptom that may be underlain by hyperparathyroidism, malignant tumors, vitamin D overdose, prolonged immobilization, or other conditions. Additional calcium in such a situation aggravates the problem: thirst, frequent urination, nausea, weakness, and arrhythmias appear.

The second absolute contraindication is hypercalciuria, that is, excessive excretion of calcium in the urine, especially if it is combined with the formation of calcium stones. Calcium is also contraindicated in nephrocalcinosis — the deposition of calcium salts in kidney tissue.

The instructions for calcium medicines additionally note individual intolerance to the components. For effervescent and chewable forms these may be sweeteners (for example, aspartame is contraindicated in phenylketonuria), flavorings, or dyes.

Kidney disease and urolithiasis

The kidneys are the main organ regulating calcium excretion. In chronic kidney disease this mechanism is disrupted, and at the same time the metabolism of phosphorus and vitamin D changes. For people with CKD, calcium and its doses are prescribed only by a nephrologist, because in some situations calcium salts are used as phosphate binders, while in others they are restricted because of the risk of vascular calcification.

With urolithiasis the situation is ambiguous. Prospective data from Curhan and colleagues showed that adequate dietary calcium is associated with a lower risk of stones, because it binds oxalates in the intestine. Therefore people with calcium-oxalate stones are usually not forbidden dietary calcium.

Supplements, however, are a different matter. In the Women's Health Initiative study, calcium supplements with vitamin D were associated with an increased incidence of kidney stones. For a person who has already had stones, this is a strong argument not to start taking them without consulting a urologist.

If the doctor considers a supplement advisable, they may order a 24-hour urine test for calcium, oxalates, and citrate, recommend a particular form (often citrate), and taking it strictly with food. It is not advisable to make such a decision on your own.

Endocrine and granulomatous conditions

Primary hyperparathyroidism is a disease in which the parathyroid glands produce an excess of parathyroid hormone. It is one of the most common causes of hypercalcemia in adults. For people with such a diagnosis, calcium supplements are selected by an endocrinologist, who assesses blood and urine calcium levels.

Sarcoidosis and other granulomatous diseases (tuberculosis, some lymphomas) are accompanied by extrarenal formation of the active form of vitamin D — calcitriol. Because of this the intestine absorbs more calcium, and even ordinary supplement doses can provoke hypercalcemia.

Conditions with prolonged immobilization also require caution — for example, after injuries in athletes. During complete immobilization the bones intensively lose calcium, its level in the blood and urine rises, and additional intake may be undesirable.

In hypothyroidism calcium is not contraindicated, but it is critically important not to take it at the same time as levothyroxine: calcium reduces the absorption of the hormone, which can lead to inadequate control of the disease.

• Primary hyperparathyroidism — only under the supervision of an endocrinologist.
• Sarcoidosis, tuberculosis, lymphomas — risk of hypercalcemia even at ordinary doses.
• Prolonged immobilization — discuss the advisability with a doctor.
• Hypothyroidism under treatment — separate calcium and levothyroxine by at least 4 hours.

Drugs with which calcium is incompatible or requires an interval

Some interactions do not make calcium contraindicated but require strict separation of doses in time. Tetracycline antibiotics and fluoroquinolones form insoluble complexes with calcium; taking them at the same time can reduce the effectiveness of infection treatment.

Bisphosphonates, prescribed for osteoporosis, are taken on an empty stomach and separately from any calcium preparations, otherwise they are practically not absorbed. Iron and zinc preparations are also absorbed worse alongside calcium.

More dangerous interactions are with thiazide diuretics, which reduce calcium excretion in the urine and, together with supplements, can cause hypercalcemia. Cardiac glycosides (digoxin) against the background of elevated calcium carry a higher risk of toxic arrhythmias. For people taking these drugs, calcium is prescribed only by a doctor.

It is also important to remember hidden sources of calcium: calcium-carbonate-based antacids, multivitamins, joint complexes. The combination of several such products with large doses of vitamin D has been described as a cause of calcium-alkali syndrome (Patel, Goldfarb, 2010).

Special groups: pregnant women, children, the elderly, athletes

During pregnancy and breastfeeding, the need for calcium does not rise above the norm for the corresponding age, because the body increases the efficiency of its absorption. However, in regions with low calcium intake the WHO recommends supplements to prevent preeclampsia. Any supplements during pregnancy must be coordinated with a doctor.

For children and adolescents, calcium supplements without indications are not recommended: in most cases the need is better met through diet. Dosages for children differ from those for adults, and the risk of accidental overdose with chewable "candies" is real.

Elderly people more often take numerous medications and have reduced stomach acidity and kidney function. For them it is especially important to consider interactions, choose a form that does not require acid, and not exceed the upper limit of 2000 mg per day.

Athletes who use large doses of vitamin D, antacids, or diuretics (for example, in weight-class sports) should remember the cumulative risk of hypercalcemia. Diuretics, by the way, are on the WADA Prohibited List as masking agents.

Editorial conclusions

Calcium supplements must not be taken in hypercalcemia, hypercalciuria, or nephrocalcinosis. These conditions require finding out the cause, not an additional mineral.

Chronic kidney disease, urolithiasis, hyperparathyroidism, sarcoidosis, and taking thiazides or digoxin are situations in which the decision about calcium is made by a doctor.

Calcium can be combined with antibiotics, bisphosphonates, levothyroxine, iron, and zinc only with a time interval.

For more on the risks and correct dosing — in our articles "Side effects of calcium," "How to take calcium: dosage, timing, duration," and "What to combine calcium with."

References

1. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academies Press; 2011.
2. Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med. 1993;328(12):833–838.
3. Jackson RD, LaCroix AZ, Gass M, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354(7):669–683.
4. Patel AM, Goldfarb S. Got calcium? Welcome to the calcium-alkali syndrome. J Am Soc Nephrol. 2010;21(9):1440–1443.
5. Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA. 2000;283(21):2822–2825.
6. World Health Organization. Guideline: Calcium supplementation in pregnant women. Geneva: WHO; 2013.
7. World Anti-Doping Agency. The World Anti-Doping Code: International Standard — Prohibited List. Montreal: WADA; чинна редакція.