Metabolites in the essential mineral selenium may help the body fight certain kinds of cancer, say researchers at the University of Copenhagen. Selenium is found naturally in a number of vegetables and nuts, as well as in fish such as salmon, tuna and cod.

In a new study published earlier this month in the Journal of Biological Chemistry, Danish scientists said these chemical compounds appear to slow down the immune system's over-response to cancer cells, particularly in melanoma, prostate cancer and some forms of leukemia.

Normally the immune system removes abnormal cells from the body, but certain cancer cells can evade detection by the immune system and instead over-activate it.

"The stimulating molecules over-activate the immune system and cause it to collapse, and we are, of course, interested in blocking this mechanism," said Soren Skov, a professor in the Department of Veterinary Disease Biology at the University of Copenhagen, in a press release. "We have now shown that certain selenium compounds, which are naturally found in, e.g. garlic and broccoli, effectively block the special immunostimulatory molecule that plays a serious role for aggressive cancers."

By blocking this over-stimulation, the immune system is left unimpaired and better able to fight the disease by removing malignant cells from the body.

The  university researchers focused on certain binding molecules, called ligands, specifically the NGK2D ligand, which enables some cancers to spread through the bloodstream.

"[Ligand] molecules are found both on the surface of the cancer cells and dissolved in the blood of the affected person," Skov said. "We are now able to show that selenium compounds appear to have a very beneficial effect when it comes to neutralizing the special variant of the NGK2D ligand."

Selenium, in small amounts, plays a key role in human metabolism and is also thought to have anti-oxidant properties that prevent cellular damage. Too much selenium is toxic to the body, however. It is not clear from the Danish research if naturally-occurring selenium in foods like broccoli and brazil nuts would produce the same anti-cancer affects as in the laboratory and if so, how much would be needed to be beneficial without also being toxic.

"If we can find ways to slow down the over-stimulation, we are on the right track," Skov said. "The new results are yet another small step towards better cancer drugs with fewer adverse effects."