Vitamin C (ascorbic acid) has been explored as a supportive agent in cancer treatment, particularly for its potential to reduce side effects of chemotherapy and radiation, and to improve quality of life in patients. The rationale stems from both its antioxidant properties and some clinical interest in high-dose intravenous vitamin C. Historically, vitamin C was popularized in the 1970s by Linus Pauling, who hypothesized its benefits in cancer care, but early studies were limited and often methodologically weak.

More recent research has focused on intravenous (not oral) vitamin C as an adjunct to conventional cancer therapies. Some small clinical trials and case reports suggest that high-dose IV vitamin C may help reduce chemotherapy-related side effects such as fatigue, nausea, and pain, and may improve overall well-being. However, these studies are generally small, not always placebo-controlled, and results are mixed. Large, well-designed randomized controlled trials are lacking, and the evidence is not strong enough to recommend vitamin C as a standard supportive therapy in cancer treatment.

Major cancer organizations, such as the American Cancer Society, acknowledge the ongoing research but caution that high doses of vitamin C can interact with some chemotherapy drugs and may not be safe for all patients. In summary, while there is some scientific interest and limited evidence supporting the use of vitamin C to reduce cancer treatment side effects, the overall quality and quantity of evidence is low to moderate (rated 2 out of 5).