Dietary supplements are advertised to people for improving their health, but years of research has shown that they may be more harmful than being beneficial. They can even increase the risk of certain types of cancer.

Dr. Tim Byers, researcher from University of Colorado, said that studies done in the past 20 years have come up with the dangers of taking extra dietary supplements.

Byers said intake of higher than nutritional levels of B vitamin called folic acid can also increase cancer, mainly colon cancer. He said that Selenium, which is generally given to try to reduce the skin cancer risk, actually increased skin cancer risk.

Dietary supplement manufacturers and distributors don’t need to obtain FDA approval.

Byers added, “What we found, in a nut shell, is that taking vitamin supplements does not reduce cancer risk. The surprising finding is that in several of these studies we found actually higher cancer risk in the groups that took supplements compared to those who took placebos”.

Byers mentioned that vitamin E supplements, normally taken to help prevent prostate cancer actually increased the risk by 17%.

Experts warned that taking above the recommended daily amount of over-the-counter vitamins may result up to 20% increase in the risk of developing cancer and heart disease. They have urged the public to get their vitamins from a healthy diet rather than relying on the pills.

These revelations would raise questions over the market for shop-bought vitamins, which as per the market research group Mintel was estimated to be worth £385 million in 2012.

According to a research done by the Food Standards Agency in 2008, it was estimated that one in three Britons took some form of dietary supplement and half of all households with children are given vitamins or minerals.

The findings have provoked Dr Byers to call for supplements to be reclassified as drugs rather than food in the US. On the basis of the contents, such supplements are either classified as medicines or food in the UK and are subject to different regulations.