An ecological study of cancer mortality rates in high altitude counties of the United States.

To test the hypothesis that sustained, increased hemoglobin levels as measured by residence in high altitudes lead to an increase of malignant cancer deaths, we performed an assessment of U.S. cancer mortality rates for people residing in high altitude counties compared with those in counties with altitudes close to sea level. This included a graphical analysis of mortality rates for all cancers, female breast cancer, respiratory system cancer (RSC) and non-Hodgkin lymphoma (NHL), computation of standardized mortality ratios (SMRs) and Poisson regression modeling. Overall, our ecological evaluation showed statistically significantly reduced SMRs and rate ratios (RRs) for high altitude residents compared to sea level residents. For the causes of death categories examined, we found no evidence that persons residing in high altitude counties are at an elevated risk of cancer mortality compared with persons living close to sea level. Our results corroborate previous altitude studies of cancer mortality.