Vitamins are accessory food factors which carry out diverse functions in the body.
Vitamin A is needed for visual function and growth, while vitamin D is needed for calcium absorption and bone formation.
The B-group vitamins, thiamine, riboflavin, nicotinic acid and pyridoxine take part as co-enzymes in a number of reactions involving the metabolism of carbohydrate, protein and fat.
The requirements of B-complex vitamins are generally related to energy intake. Two vitamins, folate and B12 are needed for haemopoiesis or the formation of red cells.
Vitamin A:
Vitamin A is essential for normal vision, for maintaining the integrity of epithelial tissues and for a wide variety of metabolic functions. Recommended vitamin A intakes for various groups as given in table.
Table: Recommended intake of vitamin A (µg/d)
Group
Retinol (µg/d)
?- carotene(µg/d)
Adult man and woman
600
2400
Pregnant woman
600
2400
Lactating woman
950
3800
Infants 0-6 months 6-12 months
350
1400
Preschool children (1-5years)
400
1600
School children (7-12 years)
600
2400
Adolescents (13-18 years)
600
2400
Vitamin D
It can be synthesized in the body in adequate amounts by simple exposure to sunlight even for 5 minutes per day.
In prescribing medicinal vitamin D under certain situations where there is minimal exposure to sunlight, a specific recommendation of a daily supplement of 400 µg is made.
Vitamin E
Vitamin E requirement is linked to that of essential fatty acids (linoleic and linolenic acids).
The requirement of vitamin E (tocopherol) suggested is 0.8mg/g of essential fatty acids.
Vitamin K
Vitamin K: no recommendation is needed for vitamin K as deficiency is not seen in India.
Occasionally vitamin K deficiency is seen at birth in prematurely born infants. A dose of 0.5 – 1.0mg vitamin K to be administered by intramuscular route
B-complex vitamins
Certain B- complex vitamin intake is related to energy intake.
Thiamine
Activity of enzyme “transketolase” is measured in different levels of the vitamin - the activity of the enzyme is low in deficiency.
Requirement of thiamine is computed by depletion – repletion studies
With low intake of thiamine, urinary excretion is also low. At an intake of 0.2mg /1000 k.cal, the excretion reaches a plateau. Therefore 0.2 mg/1000 k cal is minimum requirement + 0.3mg for cooking losses
Hence the RDA for thiamine is 0.5mg/1000kcal energy.
Riboflavin
Related to the activity of enzyme “Glutathione reductase” in RBCs.
To keep the enzyme active 0.5 – 0.7mg/1000 k cal is required. Hence the requirement of riboflavin is 0.6mg/1000k cal energy.
Niacin
The essential amino acid tryptophan is the precursor of niacin
Sixty mg of tryptophan is converted to 1mg of Niacin.
Niacin equivalents (in mg) = Niacin content (in mg) + tryptophan/60
Studies show that subjects consuming 6.5 – 7.0mg niacin equivalents/1000k.cals have satisfactory niacin status. Therefore ICMR recommends 6.6mg/1000k.cals of niacin equivalent /niacin.
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