Background: Previous research revealed that cancer death rates tend to be lower in higher land elevation areas compared to lower land elevation areas. To further investigate this relationship, a novel method is used in the present study to identify low versus high elevation areas, with an accounting of air temperatures and smoking rates as other possible determinants of cancer.
Methods: Counties in the United States that did not have overlapping land elevations (in feet above sea level, determined at the state level) were identified and categorized as having either a "low" or "high" elevation. States that were outliers for temperature and smoking rates were omitted. Using an ecological design, county cancer age-adjusted death rates (per 100,000 persons) for white persons during 2006-2010 were compared in low versus high land elevation counties in states having similar smoking rates and air temperature.
Results: Cancer death rate for lo land elevation counties (n=584 counties) was 189.6 (standard deviation [SD] 23.9) compared to the cancer death rate of 161.4 (SD 28.9) in high land elevation counties (n=162 counties), a difference that was statistically significant (p<0.0001) with a large effect size (of 1.12).
Discussion: Limitations to the study include: a) its (ecological) design, where populations, rather than known individuals are studied; b) the assumption that land elevations remain essentially unchanged over time; c) the assumption that the selected states had sufficiently similar temperatures and smoking rates; d) only one race (whites) was studied for the cancer death rates; and e) only one outcome (cancer death rates) was studied.
Conclusions: This study found lower cancer death rates in higher land elevation counties compared to lower land elevation counties, thus adding to the body of evidence on this topic. Ongoing research is indicated on the topic of land elevation-related health effects.
Keywords: Altitude, environmental factors, cancer epidemiology, physiological adaptation, methodological study