SOURCES: Kamen Simeonov, graduate student, bioinformatics program, University of California, San Francisco; Norman Edelman, M.D., senior medical advisor, American Lung Association, New York City; Jan. 13, 2015, PeerJ, online
TUESDAY, Jan. 13, 2015 (HealthDay News) -- Americans who live in the mountains seem to have lower rates of lung cancer than those closer to the beach -- a pattern that suggests a role for oxygen intake, researchers speculate.
Their study of counties across the Western United States found that as elevation increased, lung cancer rates declined.
For every 3,300-foot rise in elevation, lung cancer incidence fell by more than seven cases per 100,000 people, researchers reported Jan. 13 in the online journal PeerJ.
No one is saying people should head to the mountains to avoid lung cancer -- or that those who already live there are in the clear.
"This doesn't mean that if you live in Denver, you can go ahead and smoke," said Dr. Norman Edelman, senior medical advisor to the American Lung Association.
It's not even certain that elevation, per se, is the reason for the differing lung cancer rates, said Edelman, who was not involved in the research.
"But this is a really interesting study," he said. "It gives us useful information for further research."
Kamen Simeonov, one of the researchers on the study, agreed. "Should everyone move to a higher elevation?" he said. "No. I wouldn't make any life decisions based on this."
But the findings do support the theory that inhaled oxygen could have a role in lung cancer, said Simeonov, a graduate student in the bioinformatics program at the University of California, San Francisco.
As elevation increases, air pressure dips, which means people inhale less oxygen, Simeonov explained. And while oxygen is obviously vital to life, the body's metabolism of oxygen can have some unwanted byproducts -- namely, reactive oxygen species.
Over time, those substances can damage body cells and contribute to disease, including cancer.
Some recent research on lab mice has found that lowering the animals' exposure to oxygen can delay tumor development. But no one knows whether taking in less oxygen would affect humans' cancer risk.
According to Edelman, the oxygen theory has some "biological plausibility." But for now, it's just a theory, he said.
Of course, it's not just oxygen that varies by elevation.
Simeonov said he and colleague Daniel Himmelstein, also an M.D./Ph.D. trainee at University of Pennsylvania, tried to account for other variables, such as county-by-county differences in sunlight exposure and air pollution -- neither of which explained the link between elevation and lung cancer.
Nor did rates of smoking or obesity, or differences in counties' demographics, including education and income levels, and racial makeup.
"We asked, can anything explain this better [than elevation]?" Simeonov said. "And nothing else even came close."
What's more, he said, there was no strong correlation between elevation and rates of several non-respiratory tumors: breast, prostate and colon cancers. That, said Simeonov, suggests an "inhaled" risk factor is at work.
He was quick to add, though, that no study can account for all the variables that sway cancer risk.
A next step, said Simeonov, could be a "cohort study," analyzing data from individual people, as opposed to this county-by-county look. But it would take lab research to figure out whether oxygen exposure, specifically, might affect lung cancer development.
For some, Edelman said, the current findings might raise another question: Could taking antioxidants help prevent lung cancer? Antioxidants include certain vitamins and other nutrients that help mop up reactive oxygen species in the body.
However, Edelman stressed, "You can't make a leap like that from this study."
There's some evidence, he noted, that a diet rich in antioxidants from fruits and vegetables may help curb lung cancer risk.
On the other hand, a recent study in mice found that antioxidant supplements sped up the progression of lung cancer.
According to the American Lung Association, the best ways to cut your lung cancer risk are to avoid tobacco smoke, including secondhand exposure; test your home for radon; and make sure you have the proper protection against any chemical exposures at work.
The American Lung Association has more on lung cancer prevention.