It is believed that some kinds of vitamins can reduce the risk of different types of cancer. But, it is also a fact that intake of some vitamins in excess can increase risk of some cancers instead of decreasing it. Intake of beta carotene can increase the risk of lung cancer in smokers.

Recent study has revealed that people taking high-dose vitamins and mineral supplements might be increasing their risk of cancer without knowing it as some vitamins can increase risk of cancer.  

Professor Martin Wiseman, medical and scientific adviser for the World Cancer Research Fund (WCRF) said that many people think they can reduce their cancer risk by taking supplements, but the evidence does not support this.

Just because a dietary pattern that provides a relatively high level of a particular nutrient might protect against cancer, it does not mean that taking it in tablet form will have the same effect.

Research team emphasized that low dose supplements can help in forming "valuable safety net" that can help in reducing cancer risk. But, high dose supplements can be harmful for health. Hence it is better to improve quality of diet rather that taking high dose supplements.