The study is published in the online issue of Neurology, the medical journal of the American Academy of Neurology.
"The reasons for this trend could be a rise in risk factors such as diabetes, obesity and high cholesterol," said study author Brett Kissela, MD, MS, with the University of Cincinnati College of Medicine in Ohio and a Fellow of the American Academy of Neurology.
"Other factors, such as improved diagnosis through the increased use of MRI imaging may also be contributing. Regardless, the rising trend found in our study is of great concern for public health because strokes in younger people translate to greater lifetime disability."
For the study, researchers looked at occurrences of strokes in people between the ages 20 and 54 in the Greater Cincinnati/Northern Kentucky area during three separate, one year-long periods between July of 1993 and June of 1994, and the calendar years of 1999 and 2005. Only first ever strokes were included in the analysis.
The study found that the average age of people who experienced stroke fell from 71 years in 1993 and 1994 to 69 years in 2005. In addition, the study found that strokes among people under 55 made up a greater percentage of all strokes over time, growing from about 13 percent in 1993-94 to 19 percent in 2005.
The stroke rate in young people increased in both African-Americans and Caucasians, from 83 strokes per 100,000 people in 1993-94 in African-Americans to 128 per 100,000 in 2005 and in Caucasians from 26 strokes per 100,000 people in 1993-94 to 48 per 100,000 in 2005.
"The good news is that some of the possible contributing factors to these strokes can be modified with lifestyle changes, such as diet and exercise," said Kissela.
"However, given the increase in stroke among those younger than 55, younger adults should see a doctor regularly to monitor their overall health and risk for stroke and heart disease."