Blood Clotting — The Importance
of Calcium in the Clotting Process

What is meant by blood clotting?

Blood clotting, also called haemostasis, is a vital physiological process that protects the body from uncontrolled blood loss. As soon as a blood vessel is injured, the organism sets off a cascade of biochemical reactions that ultimately leads to the formation of a stable wound seal.

A distinction is made between primary haemostasis, in which platelets adhere to the injured vessel wall and form a provisional plug, and secondary haemostasis, in which the fibrinogen network permanently consolidates the seal. Both phases require specific cofactors — among them certain minerals.

The European Food Safety Authority (EFSA) has produced scientific opinions on the function of calcium in the context of blood clotting. On this basis, the EU Commission has published an authorised health claim.

Why blood clotting matters to the organism

The ability of blood to clot when injuries occur is one of the fundamental protective mechanisms of the human body. Blood clotting fulfils several tasks:

• Wound closure: The formation of a fibrin network seals the injured site and prevents further blood loss.
• Tissue protection: The clotting process protects surrounding tissue from pathogens entering through the open wound.
• Initiation of repair: Clotting initiates wound healing by releasing growth factors that stimulate cell repair.
• Vascular integrity: Even with the smallest micro-injuries in the vascular system, haemostasis maintains vessel tightness.

The clotting process involves more than a dozen different clotting factors that are activated in a precisely coordinated sequence. As factor IV, calcium is an integral part of this cascade and is involved in several activation steps.

The coagulation cascade: a multi-stage process

Blood clotting proceeds via two pathways — the intrinsic and the extrinsic pathway — both of which converge in the common final pathway. Calcium ions are involved as cofactors in both pathways. Without calcium, clotting factors VII, IX, and X cannot bind to the phospholipid membranes required for their activation.

In the common final pathway, the prothrombinase complex catalyses the conversion of prothrombin (factor II) into thrombin. This step, too, is calcium-dependent. Thrombin then cleaves fibrinogen into fibrin, which cross-links into a stable network and forms the final wound seal.

Calcium: more than a bulk mineral

Calcium is the most abundant mineral in the human body. Around 99 % of the body's calcium is located in bones and teeth. The remaining 1 % circulates in the blood and soft tissue, where it is needed for signal transmission, muscle contraction, and indeed blood clotting.

„Calcium contributes to normal blood clotting“ — In accordance with Regulation (EU) No 432/2012

Dairy products, green leafy vegetables, almonds, and certain mineral waters are among the natural sources of calcium. The daily reference value for calcium is 800 mg under EU regulation.

Bioavailability and absorption

Calcium absorption takes place mainly in the small intestine and is favoured by vitamin D. Oxalic acid (in spinach and rhubarb) and phytic acid (in grains and legumes) can reduce uptake, as they bind calcium. A varied diet covering different calcium sources favours adequate intake.