Vitamin C History

By Dr. Liji Thomas, MD

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.

Image Credit: Orawan Pattarawimonchai / Shutterstock.com

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 the 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

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
  • 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

• https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
• http://lpi.oregonstate.edu/mic/vitamins/vitamin-C
• https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/

Further Reading

• All Vitamin C Content
• What is Vitamin C?
• Vitamin C Physiological Function
• Vitamin C Daily Requirements
• Vitamin C Therapeutic Uses