High levels of Vitamin B6 and the amino acid methionine cut the risk by half, according to the study.

The results may be a clue to why some smokers never get lung cancer and some non-smokers or former smokers do, scientists at the International Agency for Research on Cancer (IARC) said.

Lung cancer is the most common form of the disease in the world and 90 per cent of all cases are caused by cigarette smoking. It kills 1.2 million people a year.

Around one in 10 smokers develop lung cancer - although they often die of other smoking-related causes such as heart disease, stroke or emphysema. Lung cancer is also known to kill people who never smoked or who gave up years ago.

The IARC study looked at around 900 people with lung cancer and found a link to low levels of vitamin B6 and an amino acid called methionine, which occur naturally in nuts, fish and meat.

"What we have found is that these two things are strong markers of lung cancer risk, but we have not shown they are causing that rise in risk," study author Paul Brennan is reported to have said.

"This indicates that diet may have an important role in lung cancer development, but it's still a little premature to say simply that if you change your diet and eat more foods with these vitamins then you'll change your future lung cancer risk."

Most of the patients were smokers but there were also 100 who never smoked and 260 who had quit.

Dr Brennan said the change in risk of lung cancer linked to B6 and methionine levels was the same for all three groups, although the overall risk of getting the disease was much higher in the smokers to start with.

He said, "For the two nutrients together, the risk reduction was about 60 percent. Obviously if you had a very high risk because you smoke, then a 60 percent reduction of that is quite important, although not as important as quitting smoking."

The latest findings reinforce previous research which suggested deficiencies in B vitamins may increase the probability of DNA damage and subsequent gene mutations. A Swedish study in 2005 found that women with high levels of vitamin B6 had a lower risk of developing colorectal cancer.

Pic: Michal Zacharzewski