Vitamin C (a.k.a. ascorbic acid) is required in the human body for healthy gums and skin, the synthesis of collagen (connective tissue), carnitine (a B complex vitamin), and various neurotransmitters (such as serotonin) required for normal brain function. Additionally, it is among the compounds referred to as antioxidants, which are involved in neutralizing oxidizing agents that would otherwise cause cellular damage in the body.

      The RDIs for vitamin C are reasonably straightforward and are listed in the following table. Figures for the recent National Academy of Sciences Dietary Reference Intakes study are based upon slightly different age ranges, which accounts for the overlapping age groups.

      The primary source of vitamin C in humans is dietary, as man (as well as primates and guinea pigs) is unable to naturally synthesize this compound in the body. The best sources of vitamin C include citrus fruits (oranges, lemons, limes, etc.), strawberries, peppers (red and green), collard and mustard greens, broccoli, spinach, tomatoes, potatoes, and numerous other vegetables.

      Although relatively uncommon in the developed world, the disease most often associated with vitamin C deficiency is scurvy. This disease is characterized by anemia, deterioration of gum tissue, a tendency to bleeding from mucous membranes (i.e., nose) and cutaneous tissue (skin), and induration (a hardening) of calf and leg muscles. A sufficient amount of the vitamin is retained in tissue in normal, healthy individuals to prevent the onset of scurvy for several months even if no vitamin C is consumed.

      Although vitamin C is water-soluble, it is stored in organs and tissues for several months. Sufficient vitamin C is normally consumed in the diet by most individuals, so the potential value of supplements lie in the vitamin's properties as an antioxidant.
      An important consideration when taking C in large quantities, is that this vitamin has a renal (kidney) threshold. When plasma concentrations become high enough, excess vitamin C is simply flushed from the body by excretion in the urine. Megadosing beyond your threshold (different for all individuals) results in the vitamin going in-one-end and out-the-other, in a manner of speaking.
      The value of supplemental vitamin C in high concentrations, that which does remain in the body, has been a contentious issue for many years, and continues to be so.

      Vitamin C is perhaps the most forgiving of excessive consumption. Although there have been reports of adverse responses from very large doses, such as diarrhea, gastrointestinal disturbances, and other minor effects, the most recent studies in this area suggest no significant toxicity resulting from large amounts of this vitamin. It is for this reason that results from the most recent National Academies of Science (NAS) study on Dietary Reference Intakes (DRI) have recommended a tolerable upper intake level (UL) of 2000 mg/day for vitamin C.

      Can vitamin C in larger than RDI amounts have beneficial health effects? The answer to this question is almost certainly yes, although with many qualifications. There is a mountain of data from years of research on this issue, so it is a difficult matter to sort out and there are no quick and simple answers.
      We will be adding an essay on this subject in the near future, so please check back for the latest information on vitamin C.