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Experts recommend doubling vitamin C intake

August 9, 2012

A new US review suggests that the recommended dietary allowance (RDA) for vitamin C be increased by more than 100% of the current levels for adults.

Having analyzed the available literature, the researchers found that the role of vitamin C in the primary prevention of coronary heart disease, stroke and certain cancers, in particular gastric cancer, is biologically plausible and strongly supported by observational epidemiologic data showing vitamin C’s benefits in redu-cing hypertension, endothelial dysfunction, chronic inflammation and oxidative stress (1).

Large randomized controlled trials (RCTs), which are currently considered the “gold standard” for establi-shing the efficacy of dietary supplements in chronic disease prevention, have been disappointing, showing little or no beneficial effect of vitamin C. However, the scientists argue that current RCTs, which are designed principally to test the safety and efficacy of pharmaceutical drugs in disease treatment, are ill-suited to demonstrate the efficacy in disease prevention of substances present in the human body that are required for normal metabolism, such as vitamins and other micronutrients. Thus, the lack of apparent proof of benefit provided by RCTs should not prevent further adjustments of the recommended intakes for vitamin C. Scientific evidence from human-based studies would be sufficient to justify increasing the recommended dietary allowance ( RDA) for vitamin C in the US from the current 75 mg per day for women and 90 mg per day for men to an optimum RDA of 200 mg per day for all adults. This proposed amount would ensure cell and tissue saturation, pose no health risk, and may have significant effects on public health at almost no expense.

The researchers noted that significant numbers of people in the US and around the world were deficient in vitamin C. Even at the current low RDAs, various studies in the US and Canada have found that about one-quarter to one-third of their populations are marginally deficient in vitamin C, and that up to 20% are severely deficient. The scientists agreed that it would be an opportune time to examine the totality of the scientific evidence showing that higher intakes of this vitamin could help prevent chronic diseases, as well as to discount certain clinical trials that are inherently flawed. Even if RCT designs were improved, additional studies investigating vitamin C in the primary prevention of chronic diseases would need to be extremely large and lengthy, would likely be cost-prohibitive and not be funded by federal agencies or the private industry. They will thus not be conducted in the foreseeable future.

References

  1. Frei B. et al. Authors' Perspective: What is the Optimum Intake of Vitamin C in Humans? Critical Reviews in Food Science and Nutrition. 2012; 52(9):815–829.