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close this bookScurvy and its Prevention and Control in Major Emergencies (WHO; 1999; 70 pages)
View the documentAcknowledgements
View the documentScurvy: definition
open this folder and view contentsIntroduction
open this folder and view contentsScurvy
open this folder and view contentsVitamin C
close this folderRecommended Daily Allowance (RDA)
View the documentProblem of calculating RDA for vitamin C
View the documentMinimum or optimum requirements
View the documentFactors affecting vitamin C reserves
View the documentMegadoses
View the documentHypervitaminosis/vitamin C toxicity
View the documentSupplementation frequency
open this folder and view contentsSources of vitamin C
open this folder and view contentsStrategies to prevent scurvy in large refugee populations
View the documentCosts
open this folder and view contentsConclusions and recommendations
View the documentReferences
View the documentAnnex 1
View the documentAnnex 2
View the documentAnnex 3
View the documentBack Cover
 

Problem of calculating RDA for vitamin C

The recommended daily allowances for most vitamins are remarkably similar from country to country and from year to year. However, this is not the case with vitamin C. The appropriate daily intake is still vigorously disputed by scientists, and recommended allowances not only vary from one country to another; they also change from time to time within the same country. Although everyone agrees that the minimal daily requirement for vitamin C is 10 mg or slightly less, there is little agreement regarding recommended intakes.

In the late 1930s, the League of Nations concluded that adult requirements are covered by 30 mg per day and that requirements increased during, and following, febrile conditions. In 1941, the U.S. National Research Council (NRC) issued its first edition of RDAs, which included 75 mg of vitamin C for an adult male since this resulted in tissue levels similar to those in the "synthesizing" species, e.g. guinea pigs. In 1974, the NRC issued a new set of recommendations where the adult allowance was reduced to 45 mg, on the understanding that this intake will maintain an adequate body pool of 1500 mg. In 1980, the NRC recommended a daily intake of 60 mg after estimating that only 85% of the ingested vitamin was absorbed into the bloodstream. Other RDAs (mean values for adult, moderately active, men) as of 1980, are found in Table 7.

There is some variation in the methods by which vitamin C status has been evaluated. The daily vitamin C requirement for saturation ranges from 50-77 mg when estimated from data on whole blood ascorbic acid levels, from 70-131 mg when plasma levels are being determined, and from 22-83 mg when white blood cell ascorbic acid levels are being assayed. An even wider range of 26-125 mg is observed when saturation is judged by urinary ascorbic acid excretion (Irwin & Hutchins, 1976).

Table 7. Recommended daily allowances for vitamin C

 

mean vitamin C values (mg/day)
for moderately active adult males

FAO/WHO (1970)

30

Australia, Canada, UK

30-40

Holland, India, Japan

50

Germany, Philippines, Switzerland

75

Russia

100

Studies with radio labelled ascorbic acid have shown that when doses of <100 mg of ascorbic acid are ingested by humans, the absorption efficiency may be as high as 98% (Olson & Hodges, 1987). When larger amounts are ingested, the absorption efficiency decreases to 70% at a dose of 180 mg, to 50% at 1500 mg, and to 16% at 12000 mg (see Table 8). Vitamin C absorption is increased significantly when given with food, perhaps because of a slowing of intestinal transit time. Thus, the absorption efficiency seems to be 90% or more over a range of 20-120 mg per day of usual intakes in food. Table 9 shows the daily intakes of vitamin C recommended by the joint FAO/WHO expert group (1970). It was stated that heavy physical activity may increase the need for vitamin C, but that there was no definite evidence for this.

Table 8. Absorption rates of vitamin C in relation to amounts ingested

Amount of vitamin C ingested (mg)

Absorption rate (%)

< 100

98

180

70

1500

50

12 000

16

Table 9. FAO/WHO recommended daily allowances for vitamin C

 

Vitamin C (mg/day)

Infants (0-6 months)

Breast-feeding by a well-nourished mother

Infants (6-12 months)

20

Children > 13 years and adults

30

Pregnant women (2nd and 3rd trimester)

50

Lactating women

50

The recommended intake of 30 mg of vitamin C per day would be covered by half an orange or 50 ml of citrus fruit juice; by a good-sized tomato (30 g) or a small helping (50 g) of good quality leafy vegetables; or by a large helping (120 g) of potatoes, depending, of course, on the storage and cooking methods used (WHO, 1974).

RDA for adults

Olson and Hodges (1987) have suggested 40 mg daily as the RDA for adult men on the understanding that the mean pool size of vitamin C in healthy men is about 1500 mg which is maintained by the ingestion of 60-100 mg daily. No nutritional or health benefits have been shown to result from a body pool > 600 mg. Nevertheless, because of the relatively rapid turnover of vitamin C and the possible enhanced needs resulting from stress and physical exercise, the authors suggested that a mean body pool of 900 mg could be considered adequate to meet all nutritional requirements while providing a sufficient reserve (body pool < 300 mg threshold for scurvy). This means that the daily requirement for vitamin C in adult men would be 27 mg. A 40% safety margin would make it approximately 40 mg/day. Because of variations in body size, and therefore body pools of vitamin C, the RDA for adult women was set at 30 mg/day.

RDA for pregnant and lactating women

For pregnant women, daily 5 mg and 10 mg increments in the maternal RDA for vitamin C were recommended during the second and third trimesters of pregnancy to offset losses from the mother's body pool. For lactating women, a daily increment of 25 mg was recommended during the first 6 months postpartum.

RDA for infants and children

In the absence of specific information about the body pool and turnover rate for infants, an intake of 25 mg per day was recommended based on the vitamin C content of breast milk. The recommended intake for children was to be gradually increased to adult levels as a function of age.

RDA for the elderly

In the absence of a pathological condition that would influence vitamin C absorption or renal reabsorption, no increment was recommended in intake by the elderly.

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