In support of a higher RDA for vitamin C

Researchers from Université de Lille 2 and Université de La Réunion in France have written a detailed and extensively referenced review of the current state of vitamin C supplementation.

Here are the highlights of their case for increasing the recommended daily allowance (RDA) of vitamin C supplementation to 1 gram, accompanied by a diet rich in fruits and vegetables.

The article is more than 7000 words. So, what follows is a top line summary.

Functions of vitamin C

  • Vitamin C is required for maintenance of normal connective tissue and wound healing.
  • It’s also required for bone remodeling and other metabolic reactions, among other needs.

Recommended dietary allowance of vitamin C

  • People vary widely in their vitamin C requirements.
  • The current RDA for vitamin C is based on twice the amount needed to prevent scurvy and the threshold to spill vitamin C into urinary excretion.
  • Many reviewers suggest that intake of vitamin C much higher than the RDA may reduce the risk or risk factors for chronic diseases such as heart disease and certain types of cancer.
  • But there’s no justification for routine megadose vitamin C, 1–3 grams/day, in the normal population.

Bodily needs in vitamin C

  • Needs vary among different people and under different conditions.
  • For example, the elderly have reduced concentrations of vitamin C in blood and white blood cells.
  • Vitamin C supplementation (500 mg/day for 1 month) enhanced the immune response of T lymphocytes .
  • In healthy people with higher concentrations of vitamin C (1 grams/day), white blood cells are more active and could speed their respond to infection or inflammation.

Vitamin C consumption higher than the RDA

  • Higher doses of vitamin C (2500 mg daily) taken by mouth result in higher vitamin C blood levels.
  • High levels of vitamin C protect against damage to blood vessels and reduce mortality rates in the elderly.
  • Taking hourly doses of 1000 mg of vitamin C for the first 6 hours after the onset of cold symptoms and 3 times daily thereafter decreased flu and cold symptoms by 85% vs a control group.
    • Although other studies show conflicting results.
  • Based on the literature, the authors suggest a minimum vitamin C consumption of 1 gram daily in healthy people in order to complete a prevention program for many diseases.

Safety of vitamin C supplementation

  • Gastrointestinal distress is the most common side effect of high vitamin C intake.
  • When it occurs, the vitamin C dose is usually at least 2 grams/day.
  • Symptoms usually disappear in 2 weeks.

The bottom line?
The authors state that there’s evidence that vitamin C prevents and treats a broad range of diseases. Yet, the current RDA for vitamin C does not cover the need for vitamin C in daily bodily functions.

“Consequently, even if vitamin C requirements vary greatly among individuals, it is suggested that vitamin C supplementation is not only totally safe but also necessary to achieve optimal health. Therefore, in agreement with the current literature, we advise healthy people to consume 5 servings of fruits and vegetables daily, added to 1 gram of vitamin C supplementation divided in 2 or 3 doses during the day, in order to ensure an optimal allowance in vitamin C to achieve optimal health.”

12/3/08 2:30 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.