What are vitamins?
"Vitamin" is the name given to organic compounds that are essential to life and are required in very small amounts for normal metabolic functions. Vitamers are other chemical forms of vitamins that have biological activity because they can be converted to the metabolically active form of the vitamin in the body.
With the exception of rickets, vitamin deficiencies are very rare in developed countries today, although they continue to be an important cause of morbidity and mortality in developing countries.
It is important to understand that usually deficiency of a single nutrient, with an otherwise adequate nutrition is rare. Although the signs of one deficiency may predominate, most likely there will be multiple deficiencies. Similarly, all the classic signs of a particular deficiency may not be present in each case.
Stages of Deficiency
- Depletion of body stores: Circulating levels of the vitamin usually indicate this. However, there may be problems with diagnosing vitamin deficiency on the basis of this in the case of secondary vitamin deficiencies (see below).
- Metabolic lesions: In general, metabolic abnormalities can be detected at an earlier stage than physical lesions. Two forms can be defined
- Abnormal biochemistry under normal conditions - Enzymes using the deficient vitamin as a cofactor will have reduced activity. High blood levels and excretion of intermediates of metabolism can be detected.
- Abnormal response to a metabolic challenge - Abnormal levels of metabolites are found (as above) only when large doses of precursor compounds are administered.
- Covert vitamin deficiency: In this case, the patient appears to be adequately nourished, however, any stress eg wounding, can disclose the deficiency.
- Overt clinical deficiency: This is the easily recognisable final development of the deficiency disease. There are pathological lesions and treatment is urgently required to avoid death.
- Secondary vitamin deficiency: In this case, dietary intake and body stores of the vitamin are sufficient, however there is a functional deficiency of the vitamin. This could be because there is a deficiency of the protein required for transporting the vitamin through the blood. This occurs in secondary vitamin A deficiency associated with severe protein-energy malnutrition.
Factors affecting an individual's requirements
Generally higher requirements of vitamins exist for growing children, who are metabolically more active relative to their body size, pregnant women, and women who are breast-feeding. Also, many drugs lead to the appearance of vitamin deficiency signs. An obvious example is the use of folic acid antagonists in cancer chemotherapy. Other examples include anti-epileptic drugs that interfere with vitamin D metabolism, and oral contraceptives that result in mild vitamin B6 deficiency.
Factors affecting vitamin intake
It is self-evident that an inadequate diet could lead to vitamin deficiency states. Conversely, even with an adequate diet, inadequate nutrient intake could be due to defective intestinal absorption (malabsorption). This could be because of general or specific malabsorption syndromes, or a specific pathological state such as diarrhoea. Finally, another significant factor affecting vitamin intake, is the loss of vitamins from the food due to poor cooking or storage.
Specific vitamins and their deficiencies and overdoses
A) The water-soluble vitamins:
These vitamins are absorbed along with water and dissolved in body fluids, excessive intake is generally lost through urine.
Vitamin B1 (thiamine)
Sources of thiamine include whole grain products, eggs, nuts, liver and yeast, however, it is rapidly destroyed b