CaEdit

Calcium (Ca) is a chemical element with atomic number 20 and the symbol Ca. It is the fifth most abundant element by mass in the human body, and the vast majority of it resides in bone and teeth as part of the mineral hydroxyapatite. In physiology, Ca2+ ions govern a wide range of crucial processes, including muscle contraction, neurotransmission, enzyme activity, blood clotting, and the maintenance of extracellular and intracellular signaling. Outside biology, calcium compounds such as calcium carbonate are common in rocks and have extensive industrial uses, notably in cement and lime production.

In daily life, calcium's role is most visible in bone health and nutrition. People obtain calcium from dairy products, leafy greens, fortified foods, canned fish with edible bones, and some mineral supplements. Vitamin D is a key partner in calcium metabolism, enhancing absorption in the intestine and supporting bone mineralization. The balance of calcium in the body is tightly controlled by a hormonal system that includes parathyroid hormone (PTH), calcitriol (the active form of vitamin D), and, in some species, calcitonin. For more on the chemical and physiological background, see the entries on hydroxyapatite, bone, and calcium ions.

Chemical properties

Calcium is an alkaline earth metal in Group 2 of the periodic table. It appears as a soft, silvery metal that tarnishes in air and reacts with water and oxygen to form oxides and hydroxides. In its ionic form, Ca2+ plays a central role in many biological and geochemical processes. Calcium readily forms compounds such as calcium carbonate (CaCO3) and calcium phosphate, which are abundant minerals in the Earth’s crust and in living tissue. Industrially important calcium compounds include calcium oxide (quicklime) and calcium hydroxide (slaked lime), which are used in construction, metallurgy, and environmental applications. For context on related minerals and materials, see limestone and cement.

Biological role

Calcium is essential for life, with the majority stored in the skeleton as a reservoir that can be mobilized to support metabolic needs. Bone mineralization depends on the deposition of calcium together with phosphate as hydroxyapatite, providing structural strength to the skeleton and teeth. Outside of structural roles, calcium ions serve as a ubiquitous intracellular messenger, translating signals into cellular responses in neurons, muscle cells, and many enzymatic systems. In the circulatory system, Ca2+ participates in blood clotting, and in the nervous system, it contributes to neurotransmitter release and synaptic function. The homeostasis of extracellular calcium is monitored by the calcium-sensing receptor and regulated by hormones such as PTH, calcitriol, and, in some animals, calcitonin. See also hydroxyapatite, bone, and calcium signaling for related concepts.

Dietary calcium supports bone maintenance and several physiological functions. Foods rich in calcium include dairy products, certain leafy greens, and fortified cereals and beverages. Some fish, notably with their edible bones, also provide calcium. Absorption occurs primarily in the small intestine and is enhanced by vitamin D; dietary factors such as oxalates and phytates can reduce absorption. The balance between dietary intake, intestinal absorption, bone resorption, and renal excretion determines calcium status over time.

Dietary sources and intake

Dairy products (milk, yogurt, cheese) are traditional primary sources in many cultures.
Leafy greens such as kale and broccoli provide calcium with varying bioavailability.
Fortified foods (cereal, plant milks, juice) help broaden calcium access, especially where dairy is less common.
Fish with bones (e.g., canned sardines or salmon) contribute calcium in a form that may be well absorbed.
Certain plant-derived foods use calcium salts (e.g., tofu set with calcium sulfate) as a fortification strategy.
Supplements (calcium carbonate, calcium citrate, and related forms) are used to address gaps in dietary intake, particularly in populations at risk for deficiency.

Vitamin D status and overall dietary patterns influence calcium absorption and utilization. The relationship between calcium intake and health outcomes—bone density, fracture risk, and beyond—has informed dietary guidance in many countries. See also vitamin D and bone health for complementary topics.

Health effects and controversies

Calcium deficiency can lead to impaired bone mineralization in children (rickets) and to osteomalacia in adults, underscoring calcium’s role in skeletal integrity. Conversely, excessive calcium intake, particularly from supplements, has been associated in some studies with adverse outcomes, including kidney stone formation and, in certain populations, potential cardiovascular risks. The scientific literature on calcium supplementation and health outcomes remains mixed, with studies sometimes arriving at differing conclusions about the benefits and risks of high-dose calcium intake.

From a policy and public discourse standpoint, debates often center on how aggressively to promote supplementation or fortification, especially in populations at risk of deficiency or in groups with dietary limitations. Proponents of market-driven nutrition argue for personal responsibility, informed choice, and targeted guidance rather than broad, nanny-state mandates. Critics of heavy-handed policy pointing to nutrition guidelines contend that one-size-fits-all recommendations may not reflect diverse dietary patterns, individual health needs, or the latest evidence, while emphasizing the importance of safe and accurate information about supplements, dosing, and potential interactions with medications. In this frame, it is prudent to consider both sides: the value of evidence-based guidelines and the merit of practical, voluntary consumer choices guided by qualified medical advice. See also hypercalcemia, hypocalcemia, rickets, osteoporosis, and calcium supplementation for related discussions.

Industrial and environmental context

Calcium compounds have wide industrial uses beyond biology. Calcium carbonate is a principal component of limestone and marble and is widely used in construction (as a filler or binder in cement) and in various industrial processes. Lime production from calcium oxide is essential for steelmaking, water treatment, and soil amending (agricultural lime) to raise soil pH. Calcium is also employed in metallurgy, paper production, and environmental applications, where its chemistry supports flocculation and neutralization reactions. For geologists and engineers, calcium-containing minerals are central to understanding rock formation and sedimentary processes; see limestone and cement for connected topics.

In agriculture, liming soils with calcium-containing materials helps optimize pH and nutrient availability, influencing crop yields and soil health. The broader economic implications of calcium-rich materials touch on mining, processing, and environmental stewardship—areas where policy, markets, and technology intersect to shape supply and use.