It would be fantastic if something as simple as vitamin C, found in a variety of fruits, could be used to treat cancer. But there is still no good evidence that this would work, despite more than 35 years of research. The idea of treating cancer with vitamin C was first suggested by Linus Pauling in 1976. In a small trial of 100 patients, he showed that people who took high doses of vitamin C survived longer than those who didn’t take the vitamin. But there were many problems with the study – for example, many of the people who took vitamin C had less advanced cancers. In the 70s and 80s, the Mayo Clinic tested vitamin C as a cancer treatment in three large, properly-run clinical trials. All of them found that the vitamin didn’t help against cancer. More recently, US scientists have found that vitamin C can kill cancer cells that are grown in a dish. These studies involved incredibly high doses, which could only be achieved by injecting the vitamin intravenously. Later, the same team showed that these high doses could shrink tumours in mice. However, this does not mean that intravenous injections of vitamin C would work in people. Lab-grown cells and mice are obviously very different from humans, and many chemicals have killed cancer cells only to do nothing in humans. The same team behind the recent positive results have tried giving high intravenous doses of vitamin C to cancer patients in a preliminary “phase I” trial. While the patients didn’t develop any bad side-effects, none of them saw any benefits either. The best evidence we have suggests that even if vitamin C can help against cancer, it would only have small benefits. There are also potential risks. Some laboratory and clinical studies have suggested that vitamin C could interfere with chemotherapy drugs. Also, several studies have found that taking lots of vitamin supplements (not specifically vitamin C) may contribute to an increased risk of cancer.