Calcium Intake and Risk of Cardiovascular Disease
Calcium Intake and Risk of Cardiovascular Disease
Calcium is quantitatively the most abundant mineral in the human body. An average adult's body typically contains about 1.0–1.5 kg calcium, 99% of which resides in bones and teeth. Besides the structural role in the skeleton, calcium is a vital electrolyte that is required for many critical biologic functions, including muscle contraction, vascular tone, nerve transmission, and many enzyme-mediated processes. Intracellular calcium ion levels (Ca) are typically 103- to 104-fold lower than the extracellular level. When the cell is stimulated, calcium enters the cell from extracellular compartments to activate the proper proteins in the signal transduction pathway. Upon the completion of the response, calcium is pumped outside the cell or into intracellular storage to await the next activation cycle. Calciumhomeostasis is tightly controlled by the calciotropic hormones: vitamin D, parathyroid hormone, and calcitonin. These hormones regulate calcium absorption from intestine, excretion or re-absorption from kidney, and deposition or release from bone. As a result, the circulating level of calcium is usually maintained constant in the range of 1.0–1.2mmol/L. Unless there is prolonged and severe calcium deficiency, the calcium level in blood is rarely compromised. Excessively high levels of calcium in blood – known as hypercalcemia – rarely occur due to excessive dietary or supplemental calcium intake, but more commonly result from primary hyperparathyroidism or malignancy. Hypercalcemia can cause many medical disorders, such as renal insufficiency, vascular and soft tissue calcification, and kidney stones.
3. Metabolism and Physiologic Significance of Calcium
Calcium is quantitatively the most abundant mineral in the human body. An average adult's body typically contains about 1.0–1.5 kg calcium, 99% of which resides in bones and teeth. Besides the structural role in the skeleton, calcium is a vital electrolyte that is required for many critical biologic functions, including muscle contraction, vascular tone, nerve transmission, and many enzyme-mediated processes. Intracellular calcium ion levels (Ca) are typically 103- to 104-fold lower than the extracellular level. When the cell is stimulated, calcium enters the cell from extracellular compartments to activate the proper proteins in the signal transduction pathway. Upon the completion of the response, calcium is pumped outside the cell or into intracellular storage to await the next activation cycle. Calciumhomeostasis is tightly controlled by the calciotropic hormones: vitamin D, parathyroid hormone, and calcitonin. These hormones regulate calcium absorption from intestine, excretion or re-absorption from kidney, and deposition or release from bone. As a result, the circulating level of calcium is usually maintained constant in the range of 1.0–1.2mmol/L. Unless there is prolonged and severe calcium deficiency, the calcium level in blood is rarely compromised. Excessively high levels of calcium in blood – known as hypercalcemia – rarely occur due to excessive dietary or supplemental calcium intake, but more commonly result from primary hyperparathyroidism or malignancy. Hypercalcemia can cause many medical disorders, such as renal insufficiency, vascular and soft tissue calcification, and kidney stones.