Calcium in adults

Calcium is the most abundant mineral in the body and is found in most tissues.

1. Calcium in bones

a. Role of calcium in bones

In the adult body, there is about 1200 g of calcium and 99% of that calcium is in the bones in the form of calcium hydroxyapatite salt. Calcium along with phosphorus is the main inorganic component of bones, participating in the formation of bones and teeth, ensuring strong bones and teeth.

Bone tissue acts as a source of calcium and provides calcium for metabolic needs, maintaining a stable calcium homeostasis through the balance between the two processes of bone formation and bone resorption.

Bone mineralization is the final process of bone formation, where calcium and phosphorus are deposited in the organic matrix of the skeleton, creating strong bones.

b. Consequences of calcium deficiency

Calcium deficiency and disorders related to calcium metabolism into bones are the main causes of osteoporosis and osteomalacia in adults. Osteoporosis is associated with aging, characterized by a decline in bone structure due to bone mineral content (BMC) and bone mineral density (BMD).

Osteoporosis increases the fragility of bones and, therefore, puts a person at increased risk of fractures, especially in the vertebrae, hips, and forearms.

Osteomalacia is an abnormal condition of bone mineralization and deposition of calcium into the matrix of bone structure leading to soft bones, prone to warping and breaking. Osteomalacia is known to be caused mainly by calcium and/or vitamin D deficiency.

2. Extra-bone calcium:

Extra-bone calcium accounts for 1% of total calcium and is found in extracellular fluid and soft tissues. Normal plasma calcium concentrations are maintained between 8.5-10.5 mg/100 dL (2.1-2.6 mmol/l). About 40% of total calcium is bound to plasma proteins, mainly albumin. About 50% of total calcium is in the ionized free form, which is the most important biologically active form. The remainder is attached to other inorganic compounds such as phosphate and citrate.

a. Role with the nervous system

Calcium has an important role for nerve activity, is the transmitter of nerve impulses between neurons. When the body lacks calcium, the conduction activity of the nervous system declines, making the patient prone to nervous tension, memory loss, irritability, nervous weakness.

When serum calcium is low, the ability of neuromuscular cells to inhibit sodium channels decreases, causing an increase in spontaneous action potentials of muscle cells or nerves that innervate them, leading to neuromuscular excitability. Clinical symptoms of hypocalcaemia such as: back muscle spasms, leg cramps. Severe hypocalcemia when plasma calcium levels are < 7 mg/dL (< 1.75 mmol/L) can cause tetany, laryngospasm, or generalized convulsions.

b. Muscle contraction activity

Calcium participates in muscle contraction: increasing intracellular calcium concentration in skeletal and smooth muscle activates proteins, leading to muscle contraction. This increase varies in which cells, depending on nerve excitability, hormones, muscle fiber tension and chemical concentration in the fiber.

Calcium also regulates the smooth muscle contractions of blood vessels, which in turn can regulate blood pressure. Studies also show that a diet rich in calcium helps reduce arterial blood pressure, especially salt-sensitive hypertension.

c. A coagulation factor

Calcium is a coagulation factor IV, participating in the activation of other clotting factors and the formation of blood clots that seal the wound.

d. Heart activity

The heart’s contractile activity is controlled by calcium in the blood. Studies show that, when calcium moves into the heart muscle cells, it stimulates contraction and creates excitement for the heart valves. When calcium levels are stable, this activity takes place rhythmically and the heart rate is maintained in a stable manner. However, when the calcium in the blood is low, the amount of calcium supplied to the heart’s contraction activity is not enough, leading to a decrease in heart rate, causing arrhythmia.

References:

1. “Overview of Calcium – Dietary Reference Intakes for Calcium and Vitamin D – NCBI Bookshelf”. https://www.ncbi.nlm.nih.gov/books/NBK56060/ 
2. Pham Thi Minh Duc, Physiology. Medical Publishing House, 2018.
3. Pham Van Phu, Basic Nutrition. Medical Publishing House, 2016.
4. “Hypocalcemia”. http://viendinhduong.vn/vi/tin-tuc/ha-canxi-mau.html 

Article source: Nutrition Research and Development Institute (https://inrd.vn/)

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