Methods: An ecologic study design was used with 3,108 counties in the contiguous US. Multiple data sources were accessed and assessed using descriptive statistics and regression techniques. 

Results: Life expectancy positively correlates with higher altitude and lower average daily sunlight, maximum air temperature, fine particulate matter, and precipitation. However, after accounting for lower average daily maximum air temperature, fine particulate matter, and precipitation, which correlate with higher altitude, higher altitude and lower average daily sunlight now associate with poorer life expectancy. After accounting for lower temperature and other natural environmental factors, counties with better overall health behaviors tend to have lower altitude and average daily maximum air temperature and precipitation, but higher sunlight. A negative association between life expectancy and fine particulate matter is small. In the fully adjusted model, the amount of variation in life expectancy explained by altitude is 1.4%, average daily sunlight is 6.8%, maximum air temperature is 15.1%, fine particulate matter is 0.2%, and precipitation is 2.7%. After also including the health behavior index in the model, these percent contributions become 1.0%, 0.5%, 1.9%, 0.0%, and 0.5%, respectively. 

Conclusions: After accounting for higher sunlight and lower ambient air temperature, fine particulate matter, and precipitation that occur at higher altitudes, altitude correlates with lower life expectancy. The effects of these natural environmental variables on life expectancy are largely mediated by the health behaviors considered.