Vitamin C Requirements and Reference Intakes

There have been two major studies of ascorbate requirements in deple-tion/repletion studies, one in Sheffield during the 1940s (Medical Research Council, 1948) and the other in Iowa during the 1960s (Baker etal., 1969,1971 Hodges etal., 1969,1971). In addition, Kallner and coworkers (1979,1981) have determined the body pool of ascorbate and the fractional rate of turnover under various conditions. Levine and coworkers (1995, 1996, 1999) have measured plasma and leukocyte ascorbate in studies of subjects maintained on more than minimally adequate amounts of vitamin C for relatively prolonged periods of time to determine optimum, rather than minimum, requirements. 

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Although the minimum requirement for vitamin C is firmly established, there are considerable discrepancies between the reference intakes published by different national and international authorities (see Table 13.3), with figures ranging between 30 to 90 mg per day. This is the result of the use of different criteria of adequacy and reflects differences of opinion as to what represents an adequate intake of vitamin C. It is possible to produce arguments to support reference intakes of between 30 to 100 mg per day. 

Carr and Frei (1999b) reviewed studies of vitamin C intake associated with reduced risks of cancer and cardiovascular disease and suggested that, by this criterion, the average requirement was 90 to 100 mg per day, giving a reference intake of 120 mg per day. 

There is a school of thought that human requirements for vitamin C are considerably higher than the reference intakes discussed previously. Pauling (1970) measured the vitamin C intake of gorillas in captivity, assumed that this was the same as their intake in the wild (where they eat considerably less fruit than under zoo conditions), and then assumed that because they had this intake, it was their requirement - an unjustified assumption. Scaling this to humans, he suggested a requirement of 1 to 2 g per day. He also quoted the rate of... 

The requirement for vitamin C to prevent clinical scurvy is less than 10 mg/day. However, at this level of intake wounds do not heal properly because of the requirement for vitamin C for the synthesis of collagen in connective tissue. An intake of 20 mg/ day is required for optimum wound healing. Allowing for individual variation in requirements, this gives a reference intake for adults of 30 mg/day, which was the British RDA until 1991 and is the United Nations Food and Agriculture Organization/ World Health Organization RDA. 

LRNI, Lower Reference Nutrient Intake RNI, Reference Nutrient Intake Al, Adequate Intake RDA, Recommended Dietary Allowance. Sources UK Department of Health (1991) Dietary Reference Values for Food Energy and Nutrients for the United Kingdom, Report on Health and Social Subjects No. 41. London HMSO. USA Food and Nutrition Board, Institute of Medicine (2000) Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC National Academy Press. WHO/FAO WHO/FAO (2002) Human Vitamin and Mineral Requirements. Report of a Joint FAO/WHO Expert Consultation, Bangkok, Thailand. Rome WHO/ FAO. 

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