Vitamin C appears to be relatively nontoxic, although intake levels above 1 gram/day can cause nausea and diarrhea.117,132 The tolerable upper intake level for adults is 2000 mg.117 Potential problems with pharmacological doses may also include “rebound scurvy,” which occurs when the intake of high levels is abruptly stopped. In excess states (>4 gram/day), high levels of ascorbate and, significantly, one of its metabolites, oxalate, are found in urine and may increase the risk of renal-oxalate stone formation. The latter is pertinent, as it accounts for one of the few potential clinical toxicities of systemic vitamin C supplementation.
Summary
The current RDA of vitamin C for nonsmoking women and men is 75 mg and 90 mg, respectively. The totality of the reviewed data suggests these dosages of vitamin C are optimal in this population both as an essential nutrient as well as an effective antioxidant. Several populations warrant special attention with respect to vitamin C requirements. These include patients with periodontal disease, smokers, pregnant and lactating women, and the elderly. However, even in these subpopulations, the data do not support recommending the routine daily intake of more than 200 mg of vitamin C. While higher dosages are generally well tolerated, the tolerable upper level of vitamin C is 2 g. In response to the aggressive promotion and advertising by health food advocates related to the use of nutritional supplements and antioxidant, patients may seek information from their dentist, a trusted source, about holistic issues. Clinicians should be cognizant about such issues and should be prepared to provide their patients with evidence-based recommendations. In their comprehensive approach to patient care, clinicians should base the need for recommending dosages in excess of the RDA on sound data supported by a nutritional analysis and the patients’ plasma vitamin C concentration (normal: >0.2 mg/dl) levels.
Vitamin C appears to be relatively nontoxic, although intake levels above 1 gram/day can cause nausea and diarrhea.117,132 The tolerable upper intake level for adults is 2000 mg.117 Potential problems with pharmacological doses may also include “rebound scurvy,” which occurs when the intake of high levels is abruptly stopped. In excess states (>4 gram/day), high levels of ascorbate and, significantly, one of its metabolites, oxalate, are found in urine and may increase the risk of renal-oxalate stone formation. The latter is pertinent, as it accounts for one of the few potential clinical toxicities of systemic vitamin C supplementation.
