XPost: alt.survival, sac.politics, alt.support.stop-smoking
XPost: alt.health
Epidemiologists have long been puzzled by a strange pattern in
their data: People living at higher altitudes appear less likely
to get lung cancer.
Associations like these can be notoriously misleading. There is,
for instance, a strong correlation between per-capita cheese
consumption and the number of people strangled accidentally by
their bedsheets. Slice and dice the profusion of data, and there
is no end to the coincidences that can arise. Some were recently
collected in a book called “Spurious Correlations.” Year by
year, it turns out, the number of letters making up the winning
word for the Scripps National Spelling Bee closely tracks the
number of people killed by venomous spiders.
These are probably not important clues about the nature of
reality. But the evidence for an inverse relationship between
lung cancer and elevation has been much harder to dismiss.
A paper published last year in the journal PeerJ plumbed the
question to new depths and arrived at an intriguing explanation.
The higher you live, the thinner the air, so maybe oxygen is a
cause of lung cancer.
Oxygen cannot compete with cigarettes, of course, but the study
suggests that if everyone in the United States moved to the
alpine heights of San Juan County, Colo. (population: 700),
there would be 65,496 fewer cases of lung cancer each year.
This idea didn’t appear out of the blue. A connection between
lung cancer and altitude was proposed as early as 1982. Five
years later, other researchers suggested that oxygen might be
the reason.
But the authors of the PeerJ paper — two doctoral students at
the University of Pennsylvania and the University of California,
San Francisco — have made the strongest case yet. At the
University of Pennsylvania Medical School, the paper won last
year’s Abramson Cancer Center prize for basic research. And in
July it was chosen as one of PeerJ’s best papers on cancer
biology.
Skeptics were quick to strike back, though not very effectively.
A would-be debunking on the Cancer Research UK website was
quickly followed by a debunking of the debunking.
All of the usual caveats apply. Studies like this, which compare
whole populations, can be used only to suggest possibilities to
be explored in future research. But the hypothesis is not as
crazy as it may sound. Oxygen is what energizes the cells of our
bodies. Like any fuel, it inevitably spews out waste — a
corrosive exhaust of substances called “free radicals,” or
“reactive oxygen species,” that can mutate DNA and nudge a cell
closer to malignancy.
That is not a good reason to consume antioxidant pills. While
the logic may seem sound, there is no convincing evidence that
these supplements add to nature’s already formidable means of
repairing oxidative damage — and they may even disrupt some
delicate biological balance, increasing cancer risk and speeding
tumor growth.
But there is no question that oxidation, so crucial to life,
rusts our cells and can edge them closer to becoming cancerous.
In examining the possibility that breathing itself significantly
increases the risk of lung cancer, the authors of the paper,
Kamen P. Simeonov and Daniel S. Himmelstein, began by
eliminating confounding variables. Maybe younger, healthier
people tend to live at higher altitudes, with older and weaker
ones, including smokers, retreating to lower lands. That could
create the illusion of a protective altitude effect, but one
that has nothing to do with oxygen.
The authors also took into account factors like income,
education and race, which affect access to medical care. To
reduce distortions caused by noisy data, the researchers
excluded counties with large numbers of recent immigrants, who
might have acquired cancer-causing mutations elsewhere. Also
ruled out were places with a large number of Native Americans,
whose cancer rates often go underreported.
Beyond the human variables were geophysical ones. Air at higher
altitudes may be less polluted by carcinogens. And since
sunlight exposure is more intense, maybe the increase in vitamin
D helps stave off lung cancer — an idea previously suggested.
Differences in precipitation and temperature might also have
some effect.
These data, too, were added to the scales, along with the
influence of radon gas and ultraviolet rays, which is greater at
higher elevations. The frequency of obesity and diabetes, which
are risks for many cancers, was adjusted for, along with alcohol
use, meat consumption and other factors.
After an examination of all these numbers for the residents of
260 counties in the Western United States, situated from sea
level to nearly 11,400 feet, one pattern stood out: a
correlation between the concentration of oxygen in the air and
the incidence of lung cancer. For each 1,000-meter rise in
elevation, there were 7.23 fewer lung cancer cases per 100,000
people. (The study found no similar correlations for breast,
colon and prostate cancer.)
That is not a good reason to inhale less deeply at sea level or
to flee to the mountains. Wherever you live, smoking accounts
for as much as 90 percent of lung cancer. Radon is considered a
distant second cause. But the PeerJ study complicates things.
For various reasons, radon levels are generally higher at higher
altitudes, while lung cancer rates are lower. Does that mean
radon is not so dangerous after all? Or are its bad effects
offset by the healthy deficit of carcinogenic oxygen?
Or maybe radon, like thinner air, protects against lung cancer.
According to a long-debated hypothesis called hormesis, the
earth’s low levels of natural radiation actually might reduce
cancer risk.
However this all shakes out, the study is a reminder that not
all carcinogens are manufactured by chemical plants. And not all
of them can be avoided. You can quit smoking and mitigate the
radon in your basement. But you can’t mitigate oxygen.
http://www.nytimes.com/2016/01/26/science/unraveling-the-ties-of- altitude-oxygen-and-lung-cancer.html?_r=1
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