The Swiss-German physician/alchemist, Paracelsus, said,in the Middle Ages, that "The dose makes the poison." According to a new study published in PeerJ, even oxygen may fall prey to the above adage. While essential to human life, aspects of oxygen metabolism may promote cancer. Capitalizing on the inverse relationship of oxygen concentration with elevation, researchers found lower rates of lung cancer at higher elevations, a trend that did not extend to non-respiratory cancers, suggesting that carcinogen exposure occurs via inhalation. In the United States, lung cancer is responsible for 27% of all cancer deaths, claiming an estimated 160,000 lives per year. While smoking is linked to as much as 90% of lung cancer cases, this new study suggests that atmospheric oxygen may play a role in lung carcinogenesis. Oxygen is highly reactive and even when it is carefully and quickly consumed by our cells, it results in reactive oxygen species (ROS) which can lead to cellular damage and mutation. While oxygen composes 21% of the overall atmosphere, lower pressure at higher elevations results in less inhaled oxygen - an effect which notoriously frustrates athletes at high altitudes. For example, across United States counties, elevation differences account for a 34.9% decrease in oxygen from Imperial County, California (-11 meters) to San Juan County, Colorado (3,473 meters). To investigate whether inhaled oxygen could be a human carcinogen, two researchers compared cancer incidence rates across counties of the elevation-varying Western U.S. They found that as county elevation increased, lung cancer incidence decreased.
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