Stroke rates have been declining in older people over the past 20 years — but have sharply increased in those under 55.

Researchers at Rutgers University used data from the New Jersey Department of Health on more than 227,000 hospitalizations for stroke from 1995 through 2014, calculating incidence by age over five-year periods. The findings appeared in the Journal of the American Heart Association.

Compared with the 1995-99 period, the rate of stroke in 2010-14 increased by 147 percent in people 35 to 39, by 101 percent in people 40 to 44, by 68 percent in those 45 to 49, and by 23 percent in the 50 to 54 group.

Stroke is still far more common in older people. But the rate decreased by 11 percent in those 55 to 59, by 22 percent in the 60 to 64 group, and by 18 percent in people 65 to 69.

The reasons are unclear, but the lead author, Joel N. Swerdel, now an epidemiologist with Janssen Pharmaceuticals, said that increasing obesity and diabetes in younger people are probably involved.

"For a person 30 to 50, the good news is you ain't dead yet," he said. "With behavioral changes, changing diet, increasing exercise, there's still hope for you. Behavioral change is hard, but this study is an early warning sign."