Vitamin C and cancer: how science is revisiting Linus Pauling's controversial theory
New research suggests that vitamin C given intravenously in very high doses may act on cancer cells somewhat like a mild chemotherapy drug, unlike oral tablets which show no such effect.
Half a century ago, two-time Nobel laureate Linus Pauling, together with physician Ewan Cameron, claimed that very high doses of vitamin C could help cancer patients live longer and feel better. Their observations were based on patients who initially received vitamin C intravenously before switching to tablets. Later, large trials by the Mayo Clinic found that vitamin C tablets did not improve survival, and Pauling's theory was largely dismissed as mistaken.
An overlooked distinction
For a long time, a key detail went unnoticed: Pauling and Cameron's patients received vitamin C by vein, while the Mayo Clinic trials used tablets only. The gut can absorb only a limited amount of vitamin C, so tablets cannot raise blood levels nearly as high as an intravenous drip, which can push concentrations tens or even hundreds of times higher.
How vitamin C may affect cancer cells
At normal levels, vitamin C acts as an antioxidant that protects cells. But at very high concentrations, particularly around tumors, laboratory studies show it can promote the formation of hydrogen peroxide, a substance capable of damaging cells. Cancer cells, already under stress and with weakened defense systems, appear especially vulnerable to this effect, while healthy cells generally survive.
What recent evidence shows
Small trials involving patients with hard-to-treat cancers, such as ovarian, pancreatic or brain tumors, suggest that most patients can tolerate large intravenous doses of vitamin C without serious side effects, except those with poor kidney function. Some studies point to possible benefits when vitamin C is combined with chemotherapy, though results remain mixed. A more consistent finding is improved quality of life, including less fatigue, pain and nausea.
Scientists caution that large, definitive trials proving intravenous vitamin C extends survival are still lacking. As a result, the approach remains experimental and should be used only within clinical trials or under close medical supervision, not marketed as a commercial "immune boost" treatment.
