Positive Health Online

Abstract

LEVINE and colleagues, Molecular and Clinical Nutrition Section, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892 USA write that recommendations regarding vitamin C intake are being revised by the Food and Nutrition Board of the National Academy of Sciences. The last recommended dietary allowance (RDA) for vitamin C of 60 mg was published in 1989; since then, extensive biochemical, molecular, epidemiologic and clinical data have become available.

Background

Methodology

The 9 criteria upon which new recommendations can be based are: dietary availability, steady-state concentrations in tissues in relationship to dose, bioavailability, urine excretion, adverse effects, biochemical and molecular function in relationship to vitamin concentration, direct beneficial effects and epidemiologic observations in relationship to dose, and prevention of deficiency. The authors applied these criteria to the Food and Nutrition Boards new guidelines, the Dietary Reference Intakes, which include 4 reference values.

Results

The estimated average requirement (EAR) is the amount of nutrient estimated to meet requirement of half the healthy individuals in a life-stage and gender group. Based upon an EAR of 100 mg/d of vitamin C, the RDA is proposed to be 120 mg per day . If the EAR cannot be determined, an adequate intake (AI) amount is recommended instead of an RDA. The AI was estimated to be either 200 mg/day from 5 servings of fruits and vegetables, or 100 mg/day of vitamin C to prevent deficiency with a margin of safety. The final classification, the tolerable upper intake level, is the highest daily level of nutrient intake which does not pose risk or adverse health effects to almost all the population. This amount is proposed to be less than 1 g of vitamin C daily .

Conclusion

Physicians may advise patients that 5 servings of fruits and vegetables per day may be beneficial in preventing cancer and providing sufficient vitamin C intake for healthy people, and that 1 g or more of vitamin C may have adverse effects in some people.

References

Levine M et al. Criteria and recommendations for vitamin C intake. JAMA 281(15): 1415-23. Apr 21 1999.

Comment

Although it is encouraging that the outrageously understated RDA for vitamin C of 60 mg is proposed to be increased to over100 mg, the caveat that 1 g or more of vitamin C could have adverse effects in some people is a trifle draconian, given that the worst side effect from consuming vitamin C to bowel tolerance is diarrhoea. Physicians have been administering tens of grams of vitamin C for many years to certain patients for mercury detoxification, HIV and other diseases.