June 15, 2010 -- Having higher blood levels of vitamin B6 and the amino acid methionine both appear to reduce lung cancer risk in smokers and nonsmokers alike, according to a new study.
"We found that vitamin B6 and methionine are strongly associated with reducing lung cancer risk in people who never smoked, those who quit, and current smokers," researcher Paul Brennan, PhD, of the International Agency for Research on Cancer in Lyon, France, tells WebMD.
Whether the link is cause and effect, he says, is not known.
In the U.S. alone, more than 219,000 new cases of lung cancer were expected in 2009, according to the American Cancer Society, with about 160,000 deaths.
The study, funded by the World Cancer Research Fund and others, is published in The Journal of the American Medical Association.
Vitamin B6 and Lung Cancer Risk: Study Details
Brennan and colleagues evaluated levels of B6 and methionine in blood samples from participants in the large European Prospective Investigation into Cancer and Nutrition (EPIC) study, which enrolled more than 519,000 participants from 10 European countries between 1992 and 2000.
His team zeroed in on 899 lung cancer cases and compared them to a group of 1,770 healthy comparison-group participants, matched to the lung cancer patients by country, sex, date of birth, and when the blood was collected.
They classified the participants into four groups, depending on blood levels of vitamin B6, which helps the body break down protein, maintain red blood cells, and perform other bodily functions, and methionine, which is involved in B vitamin metabolism.
After accounting for smoking, Brennan and colleagues found that the higher the vitamin B6 and methionine, the lower the lung cancer risk.
People in the highest group for vitamin B levels had a 56% reduced lung cancer risk, compared to those in the lowest group. Those with the highest methionine levels had a 48% reduced lung cancer risk, the researchers found.
''That's quite a strong effect," Brennan says, but emphasizes that more study is needed.
Some previous research, he says, looked only at smokers and linked vitamin B6 to a reduced lung cancer risk. His study, by including never smokers and past smokers, expands the information about the link.
Vitamin B6 is found in beans, grains, meat, poultry, fish, and some fruits and vegetables. Methionine is found in animal protein, some nuts, and vegetable seeds.
Vitamin B6, Methionine, and Lung Cancer: Behind the Results
How to explain the link is not known, the researchers say. But deficiencies in vitamin B6, for instance, may raise the risk of DNA damage and gene mutations, fostering cancer development.
Methionine is involved in a complex metabolism process with B vitamins.
Brennan cautions that the results are not a message to self-prescribe vitamin supplements. And the main message remains that people who smoke should quit, since it's the main risk factor for lung cancer, says Brennan.
Vitamin B6, Methionine, and Lung Cancer: Second View
The new study appears to be carefully done, with ''intriguing" findings, says Michael J. Thun, MD, vice president emeritus of epidemiology and surveillance research for the American Cancer Society. "However," he adds, "research on vitamins for cancer prevention has been fraught with many disappointments."
"It is therefore unwise to leap to premature conclusions." Like Brennan, Thun says the next step is to repeat the findings in another population.
''These findings should not be interpreted as evidence that smokers can substitute taking vitamin B6 for stopping smoking, nor as encouragement to take very high doses of vitamin B6, since this can have toxic effects on the skin and nervous system," Thun says.
He cautions people not to exceed the recommended dietary allowance of vitamin B6. Adults below age 50 need 1.3 milligrams a day, about the amount found in two medium bananas.