How Is Calcium Lost?

Calcium is the most abundant mineral found in bone. It is a positively charged electrolyte that is attracted to negatively charged phosphates in bone; the calcium-phosphate interaction -- important in the framework of bone -- confers strength to bone. Regulating calcium loss is an important component of calcium homeostasis or balance.

Absorption of Calcium

Calcium is obtained from dietary sources. When calcium-rich food is digested, calcium is then available for absorption; vitamin D facilitates the absorption of calcium, which minimally occurs otherwise. Most absorbed calcium is deposited in bones and only a very small percentage circulates in the blood. Blood calcium is tightly regulated to ensure proper functioning of calcium-dependent organs; when blood calcium is lower than normal, more calcium is absorbed.

Calcium Regulation

Calcium balance is maintained by regulating rates of calcium excretion in the kidneys, redistribution of calcium from bone to the blood and dietary intake of calcium and vitamin D. The thyroid and parathyroid glands are primary glands involved in calcium regulation. The kidneys regulate calcium output, whereas the intestines regulate calcium input. When blood calcium levels are low, the parathyroid glands release parathyroid hormone, which causes the release of calcium from bone into the blood. When blood calcium level are high, the thyroid gland releases calcitonin, a hormone that increases calcium removal from the blood.

Calcium Excretion

The rate of calcium excretion depends on dietary calcium intake, blood calcium levels and kidney function. The parathyroid hormone not only increases the release of calcium from bone, but it also slows urinary calcium excretion -- a beneficial mechanism in hypocalcemia or low blood calcium. Increased dietary intake of calcium results in increased blood calcium levels; parathyroid hormone release is inhibited by high blood calcium, which results in increased calcium excretion.

Preventing Excess Calcium Excretion

In a healthy person, increased calcium excretion is a compensatory mechanism that helps to normalize high blood calcium levels; in this condition, increasing calcium excretion is desired because it is one of the effective ways of normalizing blood calcium levels. Increased calcium excretion may be due to poor dietary habits, so making appropriate dietary modifications can help reduce calcium excretion. According to "The Encyclopedia of Nutrition and Good Health," a diet consisting of high protein, high phosphates -- such as in soft drinks -- or high sugar content results in increased calcium loss in the urine. Consuming high amounts of fiber may also increase calcium loss in the urine.