Vitamin C is an essential nutrient that can be synthesised by most organisms, with humans being the most well-known exception. Although the health benefits of eating fruits and vegetables are well recognized, optimal daily intake of vitamin C is still the subject of much on-going debate.
A new study in leukemia and lymphoma cell lines has shown that pretreatment with vitamin C dose-dependently reduces the effectiveness of the widely used but mechanistically dissimilar cancer drugs, doxorubicin, cisplatin, vincristine, methotrexate, and imatinib. A similar effect was seen in mice with RL cell–derived xenogeneic tumours, when vitamin C significantly reduced the effectiveness of doxorubicin in preventing growth of the tumours. All of the drugs used in the study cause depolarization of the mitochondrial membrane in the tumour cells which leads to cell death. This mitochondrial damage was inhibited in the presence of vitamin C, and probably explains why the drugs were less effective.
Although this study suggests that use of vitamin C supplements during cancer treatment may limit the effectiveness of chemotherapy, it is difficult to know what dose of vitamin C would be detrimental in patients.