A growing number of younger U.S. adults are being hospitalized for stroke, and a new study suggests that’s at least in part because more of them have risk factors like hypertension, obesity and diabetes.

When researchers examined hospital billing data on acute ischemic stroke hospitalizations for adults younger than 65 from 2003 to 2012, they found the biggest surge in stroke rates for adults aged 35 to 44. During the study period, stroke hospitalizations in that age group rose 42 percent for men and 30 percent for women, researchers report in JAMA Neurology, April 10.

The proportion of people with at least three of the five major risk factors for stroke – hypertension, diabetes, high cholesterol, obesity and smoking – rose in all age groups but soared the most, almost doubling, in adults aged 35 to 44.

“The high and rising rates of stroke risk factors among young adults is concerning and likely contributing to the increase in stroke hospitalizations over time,” said lead study author Dr. Mary George of the U.S. Centers for Disease Control and Prevention in Atlanta. “Our results stress the importance of prevention of stroke risk factors in younger adults,” George said by email.

Older people in the study, aged 55 to 64, had more strokes and were also more likely to have at least three risk factors than younger adults, the study also found. By the end of the study period, about 47 percent of men and 48 percent of women aged 55 to 65 hospitalized for stroke during the study had at least three risk factors. That compares to 35 percent of men and 32 percent of women aged 35 to 44.

In that younger age group, 66 percent of men and 57 percent of women had hypertension by the end of the study, about 48 percent of men and 38 percent of women had lipid disorders like high cholesterol, and 42 percent of men and 36 percent of women smoked.

One limitation of the study is that researchers weren’t able to examine the severity or cause of stroke, the authors note. They also lacked data on some risk factors that can influence the odds of stroke like family history or use of estrogen-based medications.

It’s also possible that the surge in strokes among younger adults might be explained in part by changes in how strokes are diagnosed, said Dr. James Burke, author of an accompanying editorial and a neurology researcher at the University of Michigan and the Ann Arbor VA Healthcare System.

Even though obesity rates are rising, the magnitude of change during the study period was small and obesity is a weak risk factor for stroke, Burke said by email. Conversely, hypertension is generally the strongest risk factor and became more widely recognized and aggressively treated during the study period, Burke added.

“So while I wouldn’t rule out an increase in conventional risk factors driving an increase in stroke in the young, if rates are truly going up, my best guess it’s for reasons other than classical risk factors,” Burke said.

Still, people can take steps to lower their risk.

“To prevent stroke in general, the story is to stop smoking, get regular exercise, watch your diet and make sure that your vascular risk factors are evaluated and well-controlled,” Burke advised.