Dietary mineral supplement
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Calcium supplements are salts of calcium used in a number of conditions. Supplementation is generally only required when there is not enough calcium in the diet. By mouth they are used to treat and prevent low blood calcium, osteoporosis, and rickets. By injection into a vein they are used for low blood calcium that is resulting in muscle spasms and for high blood potassium or magnesium toxicity.
Common side effects include constipation and nausea. When taken by mouth high blood calcium is uncommon. Calcium supplements, unlike calcium from dietary sources, appear to increase the risk of kidney stones. Adults generally require about a gram of calcium a day. Calcium is particularly important for bones, muscles, and nerves.
The medical use of calcium supplements began in the 19th century. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2021, it was the 235th most commonly prescribed medication in the United States, with more than 1million prescriptions. Versions are also sold together with vitamin D. In 2020, the combination, calcium/vitamin D was the 215th most commonly prescribed medication in the United States, with more than 2million prescriptions.
Health effects.
Bone health.
In healthy people, calcium supplementation is not necessary for maintaining bone mineral density, and carries risks that outweigh any benefits. Calcium intake is not significantly associated with hip fracture risk in either men or women. The US Preventive Service Task Force recommends against a daily supplement of calcium or vitamin D. Although a slight increase in bone mineral density occurred in healthy children from calcium supplementation, using additional dietary calcium is not justified, according to a 2006 review.
Cardiovascular impact.
There is good evidence that 1,000 mg to 1,500 mg of daily calcium supplementation can effect a modest reduction in blood pressure in adults who do not have a blood pressure condition, suggesting that achieving adequate calcium levels may have role in preventing high blood pressure.
Cancer.
The US National Cancer Institute does not recommend the use of calcium supplements for lowering the risk of cancer. There is weak evidence calcium supplementation might have a preventative effect against developing colorectal adenomatous polyps, but the evidence is not sufficient to recommend such supplementation.
Side effects.
Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal kidney failure. What constitutes "excessive" consumption is not well known and, it is presumed, varies a great deal from person to person. Persons consuming more than 10 grams/day of calcium carbonate ( of elemental calcium) are at risk of developing milk-alkali syndrome, but the condition has been reported in at least one person consuming only 2.5 grams/day of calcium carbonate ( of elemental calcium), an amount usually considered moderate and safe.
A 2023 systematic review found that calcium supplementation is not associated with myocardial infarction, stroke, heart failure admission, and cardiovascular/all-cause mortality.
Calcium supplements may contribute to the development of kidney stones.
Acute calcium poisoning is rare, and difficult to achieve without administering calcium intravenously. For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45 and 1.4 g/kg, respectively.
Interactions.
Calcium supplements by mouth diminish the absorption of thyroxine when taken within four to six hours of each other. Thus, people taking both calcium and thyroxine run the risk of inadequate thyroid hormone replacement and thence hypothyroidism if they take them simultaneously or near-simultaneously, because significant amount of T4 is adsorbed to calcium carbonate depending on gastric pH levels, preventing absorption of T4 at the intestinal level.
Absorption.
Calcium absorption in the gut is influenced by factors such as vitamin D levels, gut acidity, age, estrogen levels, and dietary fiber intake. It decreases with age, low vitamin D levels, hypochlorhydria, low estrogen levels, and a high-fiber diet. Calcium is absorbed both actively and passively in the small intestines, with low vitamin D levels impairing active absorption. Calcium absorption varies with serum 25-hydroxyvitamin D [25(OH)D] levels and is also influenced by dietary factors and genetics. Individuals vary in their ability to absorb calcium, with absorption inversely related to total dietary calcium intake, dietary fiber, alcohol intake, and physical activity, and positively associated with body mass index, dietary fat intake, and serum 1,25(OH2)D and parathyroid hormone levels.
Excretion.
Calcium is excreted from the human body primarily through urine and feces. Several factors can influence the rate of urinary calcium loss, including the intake of caffeine, protein, and sodium and low estrogen levels. Caffeine intake has been associated with bone loss, particularly in women aged 66-77 years. Women consuming more than 300 mg of caffeine per day usually experience greater bone loss in the spine than those consuming less than or equal to 300 mg per day. Genetic variants of the Vitamin D Receptor (VDR) also play a role.
Types.
The intravenous formulations of calcium include calcium chloride and calcium gluconate. The forms that are taken by mouth include calcium acetate, calcium carbonate, calcium citrate, calcium gluconate, calcium lactate, and calcium phosphate.
Vitamin D is added to some calcium supplements. Proper vitamin D status is important because vitamin D is converted to a hormone in the body, which then induces the synthesis of intestinal proteins responsible for calcium absorption.
Labeling.
For US dietary supplement and food labeling purposes, the amount in a serving is expressed in milligrams and as a percent of Daily Value (%DV). The labels indicate the weight of the elemental calcium in the supplement, not the total weight of the compound. For instance, in the case of calcium citrate, the label specifies the weight of the elemental calcium, not the entire calcium citrate compound. For calcium labeling purposes 100% of the Daily Value was 1000 mg, but in May 2016 it was revised to 1000–1300 mg. A table of the pre-change adult Daily Values and references for the revision are provided at Reference Daily Intake. Food and supplement companies had until July 2018 to comply with the labeling change.
References.
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