From the facts accumulated so far as to the functions of the inorganic salts in the human body, there is ample evidence to conclude that the inorganic ions remain in the body in a state of functional balance. It is found that almost everywhere and in every function they can be grouped into two classes.
One group having complementary effects, the other group being antagonistic. It may also be found that the interrelationship may vary according to the field of reaction. At some places two elements may have antagonistic effects, whereas at others they may help each other.
The following is a brief picture of the interrelationship amongst the more important ions:
i. Calcium and Phosphorus:
Ca and PO4 ions are generally complementary in nature. They help each other. One without the other can neither be retained in the body nor can function adequately. In the blood the relation between Ca and inorganic phosphorus is 2Ca : 1P. But in the diet an opposite ratio, i.e., 2P : 1Ca, is found optimum for absorption. Raised blood calcium reduces phosphorus and vice versa.
ii. Ca, Na, Mg and K:
Although in detail their effects vary, yet generally speaking Ca is antagonistic in many respects to Na, K, and Mg. Ca is neurosedative, whereas Na and K are neuroexcitatory. In heart, Na, K, and Ca act in a co-ordinated manner and keep up the normal function of heart.
iii. Fe, Cu, Mn:
Their functions is complementary, at least as far as haemoglobin synthesis is concerned.
iv. Cu, Mo and SO4:
The actions of copper against the other two elements are antagonistic. Copper intake remaining normal, low intake of Mo and SO4 produces Cu poisoning whereas excessive intake of the two leads to copper deficiency.
It has been mentioned that at some fields of action two elements may be complementary, but at other fields they may be antagonistic. For instance, Mg is generally antagonistic to Ca. But in bone formation Mg probably helps the phosphatase mechanism by means of which Ca salts are deposited.