The Five Worst US Cities for Life Expectancy Among the Poor

— -- Four of the five U.S. cities with the worst life expectancy among poor residents between 2001 and 2014 were in Indiana and Oklahoma, according to a new study that also examined why these residents were the most at risk.

Using Social Security data to find out how wealth and poverty affects life expectancy, researchers from Stanford and MIT examined determined the best and worst cities for the poorest residents. The findings were published today in the Journal of the American Medical Association.

The five cities where residents in the lowest income quartile had the shortest life expectancy included two cities each from Indiana and Oklahoma.

Study authors said it was difficult to pinpoint exactly why poor residents in these cities were more at risk than others. They found that the lower life expectancy did not correlate with access to medical care, pollution levels or poor "social cohesion" that could potentially cause stress.

Instead, study authors speculate that poorer residents in cities with high levels of education and income have more resources than their counterparts in depressed cities.

"Such areas may have public policies that improve health (e.g., smoking bans) or greater funding for public services, consistent with the higher levels of local government expenditures in these areas," the study authors said. "Low income individuals who live in high-income areas may also be influenced by living in the vicinity of other individuals who behave in healthier ways."

The authors said more testing is needed to truly understand why poorer residents in certain cities had shorter a life expectancy.

Dr. Stephen Woolf, professor at the Center on Society and Health in the Department of Family Medicine and Population Health, Virginia Commonwealth University, wrote an accompanying editorial in the Journal of American Medical Association reviewing the study. He told ABC News that he found the study data to show how important education is in helping combat inequality.

"The conversation we have about addressing those problems and improving access to education are important to recognize as relevant to our health," Woolf told ABC News today.

"Education is not only known to be an important predictor of health outcomes but we live in an information economy," he said, explaining that for many people born into poverty, an education is the only way to escape it. "They have no realistic outlet without getting a good education that can open doors."

In his editorial, Woolf explained that education could be used to align multiple sectors from law-enforcement to health care to media to encourage a change in public health care.

"Monetizing the health benefits of education (e.g., lower health care costs) understates the savings a more educated populace brings to the cost of safety net programs and prisons while increasing tax revenue and workforce productivity," Woolf wrote.