The Great Migration, that roughly two decade span of the early 20th century when millions of African-Americans fled the segregation and violence of the American South for the relative economic prosperity of Northern and Western cities, fundamentally altered the U.S. landscape. But a new study has found that it also shortened black migrants’ lives.

The study was published this month by the American Economic Review and found that mortality rates increased at 40 percent for black men and 50 percent for black women. Common causes of death were cardiovascular disease, lung cancer and cirrhosis. 

Duke University demographer Seth Sanders, who co-authored the study, told NBC News that the findings contradict a commonly held idea that increased economic mobility in the North automatically benefited black migrants’ physical health. “We thought what we would find was that migration north extended life and made the African-American population healthier,” Sanders said. “We actually found exactly the opposite. Urban life is stressful. Being away from your roots is probably stressful.”

Between the 1910s and 1970s roughly six million African-Americans left the Deep South for places like New York City, Chicago, Washington, D.C. and Los Angeles. The study found that if a black man lived to the age of 65, he had more than an 82 percent chance of living until 70 if he stayed in the South. In the North, those chances dropped to 75 percent. For black women who were 65, the chances of reaching the age of 70 in the South were more than 90 percent; in the North, those chances dropped to 85 percent.

In her seminal book “The Warmth of Other Suns: The Epic Story of America’s Great Migration,” Isabel Wilkerson details the toll of racism in the North. “[Black migrants] were fleeing the violence of the caste system in the South, only to be met with challenges and obstacles in the North,” Wilkerson explained to NBC News. “They were searching for ways to manage in a world that had not welcomed them… where they were met with hostility upon their arrival. I would not find it surprising that their health would suffer as a result.”

This infographic from Duke University sums up the study’s major findings:

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