Normal and Therapeutic Nutrition 3(2+1)
Lesson 8:Recommended Dietary Allowances (RDA)


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
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.


  • 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, 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.


  • 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.


  • 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.

Pyridoxine (B6)

  • Requirement varies with protein intake.
  • At an intake of 1.9mg/day prevents deficiency symptoms are seen. Hence the RDA is fixed at 2.0mg/day

Folic acid

  • An intake of 50mg of folic acid prevents deficient symptoms whereas 75mg of folic acid maintains serum and RBC levels of folic acid.
  • 100 mg folic acid is recommended/day

Vitamin B12

  • Is synthesized by gut microflora.
  • Requirement ranges between 0.1 – 1.0mg/day
  • RDA is 1mg/day
Last modified: Monday, 24 October 2011, 6:27 AM