Your average life expectancy now varies by more than 20 years depending on where you live in the United States, according to an in-depth study by the University of Washington. America's "life expectancy gap" is also predicted to grow even wider in future, with 11.5% of US counties having experienced an increase in the risk of death for residents aged 25-45 over the period studied (1980-2014). No previous study has put the disparity at even close to 20 years. "This is way worse than any of us had assumed," said [study author] Ali Mokdad. The researchers found that while residents of certain affluent counties in central Colorado had the highest life expectancy at 87 years, people in several counties of North and South Dakota, typically those with Native American reservations, could expect to die far younger, at only 66. "Inequalities will only increase further if recent trends are allowed to continue uncontested," the report states. If the figures are surprising, the factors cited in the study to explain the "large and increasing" geographic inequalities perhaps are not. The authors point the finger at differences in socioeconomic and race/ethnicity factors, the availability of - and access to - quality healthcare and insurance, and "preventable risk factors" such as smoking, drinking and physical inactivity. "You expect disparities in any country, but you don't expect the disparities to be increasing in a country with our wealth and might," Mokdad said.