Vitamin D For Dummies
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Calcium is tightly linked to many of the roles that vitamin D plays in the body. In bone health (and other physiologic systems), calcium is a key player. Calcium is a mineral that must be constantly eaten to build bone and maintain the blood level of calcium.

When people hear about calcium, they think “bone.” Bone is formed by special cells in the body. These cells make a scaffold with proteins and then calcium and phosphorus form a crystal on top of this scaffold. That’s how the scaffold gets strong — like putting concrete on top of an iron structure to make a strong building.

A baby begins to accumulate calcium in bone during the third trimester of pregnancy. Accumulation of calcium in bone continues until its peak in early adulthood. Then the amount of bone, as well as the calcium level in bone, begins its gradual decline at the rate of 1 percent per year. The decline occurs because the continual remodeling of bone switches from an excess of bone formation during growth to an excess of bone breakdown in adulthood.

Even though only 1 percent of the calcium in the body is found outside of bone, this form of calcium is critical for many functions in the body. Therefore, its level is maintained in a narrow range in the blood and tissues. Consider some of the key non-bone functions of calcium:

  • It’s essential for blood clotting.

  • It stabilizes blood pressure.

  • It contributes to normal brain function.

  • It’s critical for communicating essential information among cells.

Normally, the amount of calcium inside a cell is very low relative to the amount that’s in your blood. Cells let calcium inside in response to a large number of chemicals, such as hormones. This chemical stimulus of calcium rushing into a cell makes them perform all sorts of critical functions. For example, it:

  • Helps insulin open cells to glucose

  • Is needed for the release of chemicals that transmit a signal from a nerve cell to a target cell (for example, when a nerve tells a muscle to move)

  • Facilitates the actual process of contraction of the muscle cell

  • Assists the movement of sperm into an egg to fertilize the egg

About This Article

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About the book author:

Alan L. Rubin, MD has been a physician in private practice for more than 30 years. He is the author of several bestselling health titles, including Diabetes For Dummies, High Blood Pressure For Dummies, and Thyroid For Dummies.

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