Calcium-(Chemical symbol, Ca) Calcium (along with phosphorus) are the most abundant minerals in the human body. As we discussed in the introduction to minerals, calcium, as with other minerals, is needed in elemental form, but is mostly ingested in the body in the form of complexes. Once elemental calcium is released in the body, it is then incorporated into 1 of 2 possible forms. Most of the calcium in the human exists as calcium phospate crystals, in the bones and teeth. The calcium phosphate crystals in teeth and bones forms the cement that gives strength to them.

The other form of calcium existing in the human is pure elemental calcium, Ca⁺²(Click here for an explanation of the Ca⁺², which is called the ionic form of calcium). This ionic form functions in helping nerve impulse conduction, muscle contraction , ion transport, and signals across membranes.

Like all the chemicals that enter the body, a strict control of concentration must be maintained. If amounts of calcium (or any substance) were allowed to accumulate unchecked, illness would result. If too much calcium is voluntarily taken (eg., excess supplements) this could result in mental depression, muscle fatique, stomach cramping, and other symptoms. If calcium levels were allowed to fall too low, then depression, muscle spasm, nervous excitation, palpitations and other symptoms develop. Therefore, the body always attempts to keep the level of calcium constant. How does the body do this?

If calcium levels fall too low, then the body responds by excreting a hormone called parathyroid hormone (PTH), into the blood. PTH functions by increasing the absorption of calcium from the kidney(s). At the same time, PTH allows the kidney to shed phosphates in the urine. This helps to retain calcium, as we shall see. The reason PTH works on the kidney to retain calcium, is simply because calcium is transported throughout the body, via the blood. Some of the calcium in the blood is removed by the kidney and excreted in the urine. When the kidney begins to remove too much calcium, then PTH is secreted to stop this calcium loss. PTH is produced in the 4 parathyroid glands, which lie behind the thyroid gland.

PTH also increases the production of 1,25-dihydroxycholecalciferol. Don't let this word scare you, it's simply the chemical name for the active form of vitamin D. And as you may know, the function of this vitamin is to help in the uptake of calcium from the intestines (when you eat a meal). The active form of vitamin D also causes some of the calcium stored in your bones to exit the skeletal space and enter the blood. This brings the blood level of calcium back to normal. Keep in mind, that bones not only support your body and protect you, but also store extra calcium, for times when you need it. Since, your body is aware that it needs more calcium, it releases this PTH, and PTH goes to work, causing vitamin D production, and affecting the kidney to conserve calcium. It's that simple.

If we happen to have too much calcium in the blood, the body tries to alleviate this situation by doing several things. First of all, as you can figure, PTH, and vitamin D are no longer needed because they will only mobilise more calcium in the blood and we don't want that. We want it lowered, since it's too high now. The body reacts to this situation by secreting yet another hormone (there's a hormone for everything ! How about one for nagging housewives and husbands?). This hormone is called calcitonin and is secreted by special cells of the thyroid gland. Calcitonin decreases the resorption (taking away) of calcium from the bone and increases the loss of calcium and phosphate in the urine. By excreting excess calcium in the urine, the body is getting rid of the extra. This brings calcium levels back down to the normal range.

Calcium can be found in milk, dairy products, and calcium supplements (tablets), typically in the form of CaCO₃, (calcium carbonate), calcium lactate, or calcium gluconate. You may see different brands of calcium, such as oyster shell calcium, etc. The fact is, calcium is calcium, whether is comes from an oyster shell or a housebrick. The difference in brands is in the absorption and utilisation. For example, calcium complexed in different ways renders it more difficult to be absorbed. This is the logic in some of the more expensive calcium supplements. But do not let price lead you in the wrong direction. Remember, calcium is complexed in different forms. Some are better absorbed than others. Dietary calcium can be obtained from milk, milk products, and calcium supplements. Supplements typically contain calcium in the form of calcium carbonate (CaCO₃), calcium gluconate, or calcium lactate. In other words, a calcium atom is bonded to either carbonate (CO₃, gluconate, or lactate. But which one is absorbed the best?? Well, remember, calcium is absorbed in the gut, and vitamin D aids in its absorption. The best absorbed form seems to be oyster shell. But if you drink enough milk and consume other calcium containing foods, you are most likely obtaining sufficient amounts of calcium in your diet. Remember, too much calcium can cause stomach pains, mental depression and other uncomfortable symptoms, so keep it moderate.

Calcium is not contained in sufficient quantities in the multivitamin. This is understandable, as it would make the size of the vitamin as large as a marble, and you wouldn't want to swallow that (or would you?). Therefore, calcium has to be made into a separate tablet. Calcium is usually combined with vitamin D. Vitamin D is usually always added because of its function-to increase the intestinal absorption of calcium. You will see different RDA's (recommended daily allowances) in different countries. You will see RDA's range from 500mg/day, up to 800mg/day. With increased activity, supplemental calcium is needed, especially for lifting heavy weights, etc. Keep in mind that bones can thicken over time when subjected to weightbearing. Logically, calcium is needed.

During the menopause (period of cessation of menstruation in women) a chronic deficiency of calcium seems to accelerate the loss of bone mass. This occurs between 35 and 42 years of age. This advanced resorption of bone in postmenopausal (post= after) can lead to osteoporosis. Osteoporosis is a condition characterised by the increased occurence of bone fractures (hip, wrist, head of femur), and is a leading cause of disability amongst the older generation. Our studies show that increased calcium combined with exercise reduces bone fractures and increased calcium uptake by the bones.