Vitamin C hasn’t been proven to kill cancer cells because in previous studies, basically, the researchers were doing it wrong.

In most studies, subjects took the vitamin orally. But our guts break down the concentration of the vitamin as it passes through our system. University of Iowa researchers have shown that giving vitamin C intravenously creates blood levels that are 100-500 times higher than levels seen with oral ingestion. As this high level, vitamin C can start attacking cancer, according to a UI release about the research, which appeared in the journal Redox Biology.

In previous work, Garry Buettner, a professor of radiation oncology and a member of Holden Comprehensive Cancer Center at the University of Iowa discovered that extremely high levels of vitamin C selectively kills cancer cells, but not normal cells, in the test tube and in mice. In the new study, Buettner and his team have figured out how the vitamin does it.

Vitamin C, or ascorbate, breaks down easily and generates hydrogen peroxide. Tumor cells are much less capable of removing the hydrogen peroxide, which damages tissue and DNA, than normal cells. "Thus, cancer cells are much more prone to damage and death from a high amount of hydrogen peroxide," Buettner says in the release. "This explains how the very, very high levels of vitamin C used in our clinical trials do not affect normal tissue, but can be damaging to tumor tissue."

Physicians at UI hospitals and clinics are now testing the approach in clinical trials for pancreatic cancer and lung cancer, combining high-dose, intravenous vitamin C with standard chemotherapy or radiation. Earlier phase 1 trials indicated this treatment is safe and well-tolerated and hinted that the therapy improves patient outcomes. The current, larger trials aim to determine if the treatment improves survival.