Vitamin C does not have a toxicity per se, but in some people over 2 grams/day can lead to diarrhea and gastrointestinal distress. In addition, high intake of vitamin C increases excretion of uric acid (urate) and oxalic acid (oxalate). The structure of these 2 compounds are shown below.
Figure 9.341 Structure of uric acid1
Figure 9.342 Structure of calcium oxalate2
These compounds are the primary components of 2 types of kidney stones3. The figures below show the most common sites of pain in someone with kidney stones.
Figure 9.343 Kidney stones normally cause pain in the shaded areas4
The following video describes what kidney stones are and the symptoms that can occur if someone has kidney stones. The second link shows some pictures of kidney stones.
Calcium oxalate is one of the primary forms of kidney stones with uric acid stones being more rare3. However, a link between excretion of these compounds and actual stone formation hasn't been established. Nevertheless, high-dose vitamin C supplementation should be approached with some caution, since it is not clear whether it increases the risk of forming kidney stones5.
Linus Pauling and the common cold
The person who popularized taking megadoses of vitamin C was Dr. Linus Pauling. Dr. Pauling was a chemist and is the only person to receive 2 unshared Nobel Prizes. The Nobel Prize is a prestigious award, and Dr. Pauling was close to solving the structure of DNA. This would have likely netted him another Nobel prize, but Watson and Crick beat him to it.
Figure 9.344 Linus Pauling6
Later in his life, Pauling became convinced that megadoses of vitamin C could prevent the common cold. In 1970 his book Vitamin C and the Common Cold was released and became a bestseller. Later he came to believe that vitamin C could prevent cardiovascular disease, cancer, and combat aging7. However, critics of his beliefs countered that all megadose supplementation was doing was creating "expensive urine". This refers to the fact that the RDA is only 75-90 mg/day for adults and Pauling recommended taking 1-2 grams of vitamin C daily8. Thus, with vitamin C being water-soluble, most of the vitamin C that people on the regimen were paying to consume was being excreted in the urine, thus making it “expensive”.
A recent review of vitamin C and colds found that that routine megadoses of vitamin C do not reduce the risk of the common cold in most individuals. However, there is some evidence that it might benefit people exposed to brief periods of severe physical exercise (marathon runners) or cold environments (skiers and soldiers in subarctic conditions). There has been little research conducted in children, so it is not known whether vitamin C supplementation is beneficial in this age group9.
References & Links
- Massey L, Liebman M, Kynast-Gales S. (2005) Ascorbate increases human oxaluria and kidney stone risk. J Nutr 135(7): 1673-1677.
- Hemilä H, Chalker E, Douglas B. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub3.
Kidney Stones - https://www.youtube.com/watch?v=16ewFJ-iQtw
Kidney Stones - http://www.herringlab.com/photos/index.html