Calcium, Ca

Calcium is the most abundant mineral in the human body, with the vast majority stored in bone and teeth and a small, tightly regulated fraction circulating in blood and soft tissue. It is essential for building skeletal structure, and it also enables muscles to contract, nerves to transmit signals, blood vessels to dilate and constrict, and blood to clot normally.

What Is Calcium

Chemically, calcium is an alkaline earth metal that the body handles almost entirely as an ion, not a free metal. About 99% of the body's calcium is deposited in bones and teeth as calcium phosphate, forming the mineral scaffold that gives the skeleton its rigidity; the remaining 1% circulates in blood, muscle, and other tissue, where it is essential for cell signaling, muscle contraction, and the release of hormones and enzymes. Because the body cannot manufacture calcium, all of it has to come from the diet. Dairy products such as milk, cheese, and yogurt are the most concentrated everyday sources; fish eaten with their soft, edible bones (canned sardines and salmon) also contribute meaningfully, as do certain leafy greens, and fortified foods such as some breakfast cereals, tofu made with a calcium coagulant, and plant-based milks. In this dataset, dried dairy powders, dried herbs and spices such as basil (concentrated by dehydration, not typical serving size), and calcium-set tofu rank among the highest measured sources.

Health Benefits of Calcium

Bone health is calcium's best-established role. Harvard T.H. Chan School of Public Health, The Nutrition Source notes that calcium is one of the most important nutrients for bone health, and that adequate intake across life can slow the rate of bone loss, though it cannot completely prevent age-related decline.

Research summarized by the same source associates higher dietary calcium intake, particularly from dairy foods, with a lower risk of kidney stone formation — one cited study found men who drank two or more 8-ounce glasses of skim milk daily had 42% lower stone risk than men with minimal dairy intake.

Epidemiological research has also linked higher calcium intake to a reduced risk of colorectal adenomas; a clinical trial cited by Harvard found that 1,200 mg of elemental calcium daily for about four years was associated with a 26% reduction in new colorectal adenomas, though this evidence describes association and supplementation-trial outcomes rather than a guarantee of individual protection.

Some research reviewed by Harvard also points to a possible modest blood-pressure-lowering effect of adequate calcium intake, though the evidence is described as inconclusive and not yet sufficient to support calcium supplementation as a blood pressure treatment.

How Much Calcium You Need

Established RDA and Adequate Intake (AI) figures (Institute of Medicine/National Academies values, as reported via NIH Office of Dietary Supplements, Calcium — Health Professional Fact Sheet; this fact sheet blocked direct automated fetch and its figures were corroborated via a secondary search of National Academies-sourced data) include: infants 0–6 months, 200 mg/day (AI); 7–12 months, 260 mg/day (AI); children 1–3 years, 700 mg/day; 4–8 years, 1,000 mg/day; 9–13 years, 1,300 mg/day; adolescents 14–18 years, 1,300 mg/day; adults 19–50 years, 1,000 mg/day; women 51–70 years, 1,200 mg/day; men 51–70 years, 1,000 mg/day; adults 71+, 1,200 mg/day; pregnant and lactating teens (14–18), 1,300 mg/day; pregnant and lactating adults (19–50), 1,000 mg/day.

The Tolerable Upper Intake Level (UL) is 1,000 mg/day for infants 0–6 months, 1,500 mg/day for 7–12 months, 2,500 mg/day for children and adults 1–18 and 19–50 years, and 2,000 mg/day for adults 51 and older.

Signs of Deficiency and Excess

Chronically low calcium intake does not typically cause acute symptoms because the body pulls calcium from bone to keep blood levels stable; over time this depletion can result in osteoporosis (bones that become porous and fracture-prone), and in children, rickets, or in adults, osteomalacia (softened bones), per MedlinePlus.

At the other end, chronically excessive calcium intake — usually from supplements rather than food — can lead to hypercalcemia, a buildup of calcium in the blood. Harvard's Nutrition Source notes that experts consider that high-dose supplemental calcium can raise blood calcium enough to affect clotting or contribute to arterial hardening in some people.

Warnings & Interactions

Evidence on calcium supplements (as distinct from dietary calcium) is more cautionary than evidence on calcium from food. Per Harvard T.H. Chan School of Public Health, The Nutrition Source, some research has raised concern that calcium supplements may increase cardiovascular event risk, and supplemental (not dietary) calcium has also been associated with a higher risk of kidney stones, in contrast with dietary calcium's protective association. Very high supplemental doses have also been linked to constipation and, in some studies, a possible increase in prostate cancer risk.

Calcium can also interfere with the absorption of other minerals: large single doses can reduce the body's absorption of iron and zinc, which is one reason experts recommend keeping single calcium supplement doses to 500 mg or less and spacing them at least four hours apart from iron-containing supplements or meals, per the same source.

The upper intake levels in the previous section define the threshold above which the risk of harm (chiefly hypercalcemia and its downstream effects) rises; adults over 50 are advised to stay under 2,000 mg/day from food and supplements combined, and everyone is advised to stay under 2,000–2,500 mg/day depending on age, per the figures above.

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