The Two Forms of Calcium in the Human Body

Calcium is an essential mineral in the human body, found in two primary forms: bound calcium in bone tissue and free, ionized calcium in the blood and soft tissues. About 99% of the body’s calcium is stored in bones as hydroxyapatite, a solid, crystalline combination of calcium and phosphate. This structure provides strength, stability, and resilience to the skeleton, enabling bones to bear weight and endure physical forces. Additionally, this stored calcium acts as a reservoir, releasing calcium into the bloodstream when dietary intake is inadequate, helping to maintain calcium balance and support bone health.

The remaining 1% of calcium exists in its ionized form, circulating in the body’s fluids and playing a crucial role in various biological functions. Ionized calcium is essential for nerve transmission, facilitating the efficient transfer of electrical signals between neurons. This process supports brain function, reflexes, and communication between the nervous system and muscles. In muscle contraction, calcium enables the interaction between actin and myosin filaments within muscle cells, powering both voluntary movements, like those involved in locomotion, and involuntary actions such as the rhythmic beating of the heart and the contraction of digestive muscles.
The Two Forms of Calcium in the Human Body