Parkinsonism and Vitamin C Deficiency

A healthy adult should ingest about 120 mg of vitamin C daily. Smokers and pregnant women may require more, but this recommendation was intended to address their needs as well.²⁵ Many commercial multivitamins use the old recommended daily allowance of 60 mg, so it may be safest to recommend specifically a vitamin C tablet with at least 120 mg when ordering vitamin C replacement.

Tight control of the serum vitamin C concentration means that little additional vitamin C will be taken up by the gut beyond 200 mg orally a day, which helps minimize any concerns about long-term toxicity. It takes several weeks to deplete vitamin C from the human body when vitamin C is removed from the diet, so a patient with a previously treated deficiency of vitamin C should wait a month before a repeat serum vitamin C level measurement.

The half life of vitamin C is normally ≤ 2 hours. When renal function is intact, vitamin C in excess of immediate need is lost through renal filtration. Toxicity is rare under these conditions.²⁶ When vitamin C toxicity has been reported, it has occurred in the setting of prolonged supplementation, usually when a patient already experienced a renal injury. The main toxicities attributed to vitamin C are oxalate crystal formation with subsequent renal injury and exacerbation of glucose 6-phosphate dehydrogenase deficiency (G6PD).²⁴

Oxalate formation due to vitamin C replacement is uncommon, but patients with preexisting calcium oxalate stones may be at risk for further stone formation when they receive additional vitamin C.²⁷ This is most likely to occur when treatment with parenteral vitamin C is prolonged, which is not typical for patients with neuropsychiatric scurvy who tend to respond rapidly to vitamin C replenishment. Reports of acute hemolytic episodes among patient with G6PD deficiency receiving vitamin C exist, although these cases are rare.²⁸ Furthermore, some authors advocate for the use of ascorbic acid to treat methemoglobinemia associated with G6PD deficiency, when methylene blue is not available.²⁹ It may be reasonable to begin treatment with oral vitamin C for patients with NPS and G6PD deficiency. This is equivalent to a low-dose form of vitamin C replacement and may help avoid the theoretically pro-oxidant effects of larger, IV doses of vitamin C.³⁰

Conclusion

The recent discovery of movement disorders in scurvy has enlarged the picture of vitamin C deficiency. The cases here demonstrate how hypovitaminosis C with central nervous system manifestations may be identified and treated. This relationship fits well within the established basic science and clinical framework for scurvy, and the clinical implications for scurvy remain in many ways unchanged. First, malnutrition must be considered even when a patient’s habitus suggests he is well fed. Also, it is more likely to see scurvy without all of the classic findings than an end-stage case of the disease.³¹ In the right clinical setting, it is reasonable to think of a vitamin C deficiency before the patient develops bleeding gums and corkscrew hairs. And as is typical of vitamin deficiencies, the treatment of a vitamin C deficiency usually results in swift improvement. Finally, for those who treat movement disorders or who prescribe agents such as antipsychotics that may cause movement disorders, it is important to recognize vitamin C deficiency as another potential explanation for EPS.