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Vitamin deficiency can arise through inadequate intake, or malabsorption, or impaired utilization due to defective conversation of  vitamin to its coenzyme or tissue break-down and concomitant losses (Figure 1).Use of certain drugs such as oral contraceptives produces selective increaments in specific binding proteins or apoenzymes, thereby raising the cellular requirement for certain vitamins. These results in an abnormal redistribution of the vitamin between tissues and between various enzymes within a cell type, creating pockets of deficiency and excess- a state of relative deficiency(1,2). Interpretation of laboratory test under these circumstances becomes very difficult.

Absolute or relative vitamin deficiency would be expected to lead to specific biochemical lesions, molecular lesons( altered levels or structure of macromolecules) and disease in that order(Figure 1).Disease is however a complex entity. Very often subjects with biochemical or molecular lesions remain asymptomatic, unless there is some associated for only two vitamin deficiency diseases, viznigh blindness due to vitamin A deficiency and blood clotting defect due to vitamin K deficiency.

For the other vitamin deficiency diseases, the above mentioned cascade is not well defined. Subtle functional impairments such as reduced psychomotor performance and increased susceptbility to infections are suspected to occur even in the absence of clear cut mainifestaions of disease, but their importance in relation to human health is not fully recognized.