Calcium is important for the hardness of bones and teeth. Ninety-nine percent of the calcium in the human body is found in the skeleton. In the serum, 65% of the calcium is in ionised form, 5% is found in coordination complexes with citrate, and 30% is bound to proteins. Despite the low concentration of calcium ions in the soft tissues, they have an important function in stabilising cell membranes, transmitting sensations in the nervous system and muscle contraction. Calcium is a key part of certain enzymes (amylase) and takes part in blood coagulation processes.
Endogenous factors (age, gender, pregnancy and nursing) as well as exogenous factors, including a number of nutritional factors that effect the absorption of calcium (the amount of calcium, vitamin D, phytates, oxalates, phoshopeptides, lactose) and factors that affect the excretion of calcium through the urine (the amount of sodium, phosphorous, proteins, ammonium chloride, alcohol, caffeine), affect the availability of calcium in the organism. The portion of calcium absorbed into the body fluctuates between 20% and 40% of all the calcium that goes into our organism.
The absorption of calcium in the gastrointestinal tract takes place for the most part in the duodenum and in the upper part of the small intestine. Of course, it is important for the absorption of calcium that the calcium be in a soluble form, either as a free ion type or in the form of soluble coordination complexes.
In cases where an increased need for calcium arises (periods of rapid growth, pregnancy, nursing) certain hormones which contribute to stimulating the transfer of calcium from the intestines are activated. Here vitamin D plays an important role. Vitamin D in and of itself is not an active substance; it must be converted into the biologically active product calcitriol through a chain of reactions in the liver and kidneys. Calcitriol functions like a hormone and speeds up the synthesis of the calcium-binding proteins in the stomach’s epithelial cells. This protein delivers calcium to the cells’ cytoplasm.
The role of calcium:
- Active in building bones and teeth
- Transmission of impulses through nerve tissues
- Contributes to the effectiveness of muscle contraction
- Maintains muscle strength and responsiveness
- Plays a part in blood coagulation
- Activation of certain enzymes and hormones