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BREAKING NEWS
  Oct 09, 2018
Vitamin C History
Vitamin C History
  Oct 09, 2018

Vitamin C is an essential cofactor for mixed-oxidase enzymes which catalyze the production of many proteins such as those involved in building supporting tissue in the body.

Vitamin C absorption

It is almost completely absorbed at doses of 200-400 mg/day, and plasma concentrations plateau at 60-80 μmol/L. Excess vitamin C in the gut is largely excreted. This absorption barrier may be overcome by administration of a direct intravenous infusion of vitamin C, which leads to high plasma levels.

These will slowly return to normal via urinary excretion. At doses lower than 200 mg/day, absorption is directly proportional to the dosage. Plasma levels of vitamin C are thus controlled largely by intestinal absorption, renal reabsorption and tissue transport mechanisms.

Dietary reference intakes

Dietary reference intakes may be classified as:

  • Recommended daily allowances (RDA), which cover the amount required for normal physiological function in the vast majority of healthy people
  • Adequate intakes, which are sufficient to stave off deficiency symptoms, and which are set when the RDA has not yet been determined
  • Tolerable upper intake levels, which are the greatest doses considered safe for consumption

The following table shows the recommended daily allowance of vitamin C in various groups:

Table 1. RDA of vitamin C

Group

RDA

0-6 months

40 mg

7-12 months

50 mg

1-3 years

15 mg

4-8 years

25 mg

9-13 years

45 mg

14-18 years

65-75 mg (females and males respectively)

>19 years

75-90 mg (females and males respectively)

Pregnancy

80-85 mg (less than or above 18 years respectively)

Lactation

115-120 mg (less than or above 18 years respectively)

Smokers

RDA for respective group + 35 mg/day extra

In practical terms, five servings of fruit and vegetables a day, which comes to about two and one-half cups, are estimated to supply about 200 mg of vitamin C a day.

Low levels of vitamin C are likely in the following situations, though not overt deficiency:

  • Active and passive smokers have lower plasma vitamin C levels, probably because of the oxidative stress induced by tobacco smoke inhalation.
  • Infants fed on boiled cow’s milk or evaporated milk have lower vitamin C levels because the naturally low levels of this vitamin in cow’s milk is further reduced by boiling. Both breast milk and infant formula do, however, supply the required amounts of vitamin C.
  • Malnutrition due to restricted access to a variety of foods may cause low vitamin C levels. The reasons for poor food choices include:
    • poverty,
    • alcohol or drug abuse,
    • eating disorders,
    • food fads,
    • mental illness
    • malabsorption syndromes,
    • malignancies, and
    • end-stage renal disease patients on hemodialysis

Determination of vitamin C status

The following plasma levels have been suggested to define the baseline vitamin C status:

  • Vitamin-C replete: 60-80 μmol/L
  • Sub-optimal levels: <50 μmol/L,
  • Marginally deficient levels: <28 μmol/L
  • Severely deficient levels: <11 μmol/L

References