空気が薄いと肺がん発症率が低下、酸素が毒に？！

米国西部の地域では、標高が高くなるにしたがって肺がんの発生率が減少すると分かった。酸素でさえも毒となるのかもしれない。

標高1000mごとに7.23人／10万人減少

米国ペンシルベニア大学を中心とした研究グループが、オンライン科学誌、PeerJ誌で2015年１月13日に報告している。研究グループが米国西部の各郡のがん発生率を比較。結果として、郡の標高が高くなるにしたがって肺がんの発生率は減少していた。標高が1000m上がるごとにがんの発生率は10万人当たり7.23人の割合で減少していた。平均肺がん発生率である10万人当たり56.8人の約13％に相当する。仮に米国のカリフォルニア州インペリアル郡は標高が−11mなのに対して、コロラド州サンファン郡は3473m。酸素は34.9％減少する。米国全体がサンファン郡と同じ標高だったとすると、全米の肺がん患者は６万5000人強も減ると推定される。

文献情報

Simeonov KP et al.Lung cancer incidence decreases with elevation: evidence for oxygen as an inhaled carcinogen. PeerJ 2015;3:e705.

Lung cancer incidence decreases with elevation: evidence for oxygen as an inhaled carcinogen [PeerJ]

The level of atmospheric oxygen, a driver of free radical damage and tumorigenesis, decreases sharply with rising elevation. To understand whether ambient oxygen plays a role in human carcinogenesis, we characterized age-adjusted cancer incidence (compiled by the National Cancer Institute from 2005 to 2009) across counties of the elevation-varying Western United States and compared trends displayed by respiratory cancer (lung) and non-respiratory cancers (breast, colorectal, and prostate). To adjust for important demographic and cancer-risk factors, 8–12 covariates were considered for each cancer. We produced regression models that captured known risks. Models demonstrated that elevation is strongly, negatively associated with lung cancer incidence (p < 10−16), but not with the incidence of non-respiratory cancers. For every 1,000 m rise in elevation, lung cancer incidence decreased by 7.23 99% CI [5.18–9.29] cases per 100,000 individuals, equivalent to 12.7% of the mean incidence, 56.8. As a predictor of lung cancer incidence, elevation was second only to smoking prevalence in terms of significance and effect size. Furthermore, no evidence of ecological fallacy or of confounding arising from evaluated factors was detected: the lung cancer association was robust to varying regression models, county stratification, and population subgrouping; additionally seven environmental correlates of elevation, such as exposure to sunlight and fine particulate matter, could not capture the association. Overall, our findings suggest the presence of an inhaled carcinogen inherently and inversely tied to elevation, offering epidemiological support for oxygen-driven tumorigenesis. Finally, highlighting the need to consider elevation in studies of lung cancer, we demonstrated that previously reported inverse lung cancer associations with radon and UVB became insignificant after accounting for elevation.

●訂正（2015/1/25）・文献情報に誤りがありました。お詫びして訂正いたします。