High concentrations of vitamins C, E, B6, and B12 can promote the growth of cancerous tumors, American dietitian Nichole Andrews told The Daily Mail, the latter reports.

The specialist explained that common vitamin C supplements are advertised as boosting the immune system. Some people take them in excessive doses in an attempt to improve their health, but doing so can have the opposite effect.

The reason is that the body is not able to process the excess vitamins fast enough; active substances can attack healthy cells and stimulate the growth of cancerous tumors. In addition, when excess vitamins enter the blood, they form free radicals, unstable chemical particles that trigger the oxidation process of cells and cause various mutations in them.

Research has shown that inadequate intake of vitamins can be harmful to people who have already been diagnosed with cancer. Thus, researchers from Karolinska Institutet in Sweden have found that when cancer patients and those at an increased risk of the disease took vitamin C and E supplements, new blood vessels formed within lung cancer tumors.

Additionally, a study from The Ohio State University found that male smokers who took high doses of vitamins B6 and B12, which are meant to help red blood cells form, had a four-fold increased risk of lung cancer compared to men who didn't take the supplements.

Andrews added that many vitamin supplements are incorrectly labeled and their actual dosage is unknown, making it difficult to assess the health risks of taking them.