The U.S. may be a leading global superpower, but not all of its citizens share in the high quality of life that the country is so often associated with. This national inequality is highlighted by a new study that reveals that life expectancy in America’s lowest-income regions is similar to that of some of the world’s most impoverished countries, while the richest 1 percent of Americans live longer than anyone else on Earth.

Researchers from a collection of institutions calculated this mortality gap by examining 1.4 billion tax records, dated between 1999 and 2014, and cross-referencing these with death records. In doing so, they were able to identify trends regarding income levels and the age of death in different areas of the country, publishing their findings in the Journal of the American Medical Association.

Results are alarming and staggering in equal measure, with the richest 1 percent of men living an average of 14.6 years longer than the poorest 1 percent nationwide, while the equivalent gap for women was 10.1 years. Commenting on these findings, study co-author Michael Stepner says “the fact [poorer people] can on average expect to have 10 or 15 fewer years of life really demonstrates the level of inequality we've had in the United States.”

Putting this into a global perspective, the researchers explain that low-income men from parts of Indiana, Florida and Nevada have a life expectancy of 72.7 years, which is similar to the reported male life expectancy in Sudan and Pakistan. In contrast, high-income men from New York can expect to live for 87.3 years, which is longer than any other men on the planet.

For women, life expectancy was found to range from 78.8 years to 88.9 years, with a direct correlation to income levels.

On the whole, this gap appears to be widening, with life expectancies having risen by 2.34 years for men and 2.91 years for women from the richest 5 percent of Americans during the 15-year period under consideration. Meanwhile, men and women from the country’s poorest 5 percent have experienced increases of just 0.32 years and 0.04 years respectively.

^{Inequality in the U.S. is much greater than many people think. Enrique Ramos/Shutterstock}

However, while the overall nationwide pattern is pretty clear, the researchers point out that a great deal of regional variation can be seen in the data, with the mortality gap between rich and poor actually narrowing in some parts of the U.S. during this period.

Interestingly, the study authors claim that there is no connection between access to healthcare and life expectancy, indicated by the fact that medical expenditure and health insurance premiums showed no strong correlation to the age of death.

Rather, the researchers found that lifestyle factors such as diet and smoking were the most reliable predictors of life expectancy in any given area. Furthermore, low-income people living in regions with high numbers of immigrants and college graduates, as well as high government expenditure, tend to live longer than poor people in other parts of the U.S.

Though more research is needed to determine why this is the case, the study authors suggest that highly educated populations may help to create a more health-conscious culture, and that government spending on implementing public policies like smoking bans could also contribute to this.