Urban-dwelling millennials are having strokes at alarming rates -- and scientists can't figure out why

A new Scientific American analysis of stroke trends reveals that millennials are having more strokes than ever before -- and that risk factors include living in large cities in the Midwest and on the west coast.

Along with higher risk factors based on living in West and Midwestern urban centers (rather than rural areas), the analysis also found that strokes in millennial women spiked 32 percent between 2003 and 2012, and 15 percent in men of the same age group.

The analysis notes that although young people living in the Southeastern U.S. tend to be at higher risk for other health disorders, "in western cities with more than one million residents, for example, the analysis found strokes increased about 85 percent during the 2003 to 2012 time period." The Midwest saw increases of 34 percent among their millennial populations in that time frame, whereas the same age group living in the South did not experience significant increases in strokes.

While stroke experts and analysts are baffled as to why this increase is occurring specifically in that region, "pollution might be a contributing factor, which could help explain the higher rates in urban settings," according to Mitchell Elkind, a Columbia University stroke expert interviewed for the report.

Ralph Sacco, the president of the American Academy of Neurology, told Scientific American that although "data has been scant" about strokes in younger populations, some risk factors have been identified, including drug use and other lifestyle factors.

“There has been mounting evidence from different studies suggesting that even though the incidence and mortality of stroke is on the decline, the rates may not be dropping quite as much—and even [may be] increasing—among younger populations,” Sacco told the magazine. “The reasons for these trends are not entirely clear but there are concerns about obesity, diabetes and physical inactivity having a greater impact in younger stroke victims.”