Every 40 seconds, someone in the United States has a stroke.

That’s despite the fact fewer people are dying from strokes in the U.S. and in other developed countries.

In fact, in 2013 strokes dropped from the fourth to the fifth leading cause of death in the U.S.

However, some studies suggest an exception to this trend.

Strokes in younger people may actually be on the rise, even though only about 10 percent of strokes occur in people between the ages of 18 and 50.

According to several U.S. studies and other research in Norway and France, more adults under the age of 55 are having strokes.

That rising trend is associated with what Mary George of the U.S. Centers for Disease Control and Prevention (CDC) calls “traditional, modifiable” risk factors like obesity, high cholesterol, and high blood pressure — conditions usually associated with older adults.

Read More: Get the Facts on Strokes »

Specific Kind of Stroke

The kind of stroke that seems to be on the rise is ischemic stroke.

Ischemic strokes are the most common form of stroke and happen when a blockage cuts off blood supply to the brain.

Much less common are hemorrhagic strokes, which are caused by burst blood vessels in the brain.

From analyzing nationwide hospital records, George and colleagues found an increase in young people being admitted to the hospital for strokes between 1995 and 2008. Another study in Ohio and Kentucky showed similar results: more strokes in young people in 2005 than in 1999.

Despite these studies, some experts say it’s not totally clear what is happening.

Mitchell Elkind, a neurologist at Columbia University, thinks stroke diagnoses might be on the rise rather than strokes themselves.

With access to better imaging techniques such as MRIs, doctors today are more likely to find evidence of stroke than in the past, when strokes might have been misdiagnosed as migraines or seizures.

It takes a while to figure out trends over time, he told Healthline.

Heather Fullerton, a neurologist at the University of California San Francisco, and her colleagues are currently conducting a study on the degree to which risk factors like diabetes and hypertension are causing strokes in younger people.

“We don’t have any published results yet, but my sense is that those risk factors aren’t causing stroke in children, but definitely are contributing to stroke in young adults, especially by late 30s to early 40s,” she wrote in an email to Healthline.

“[That] means those risk factors probably need to be identified and controlled at a much younger age than is currently the standard in order to prevent stroke in the young,” she said. “These factors are likely present for many years before they finally manifest in a stroke.”

Read More: High Blood Pressure in Young People Linked to Obesity Epidemic »

Diet, Lifestyle, Drugs

Many of those risk factors are associated with poor diet and sedentary lifestyle. But strokes in the young can also be attributed to use of drugs like cocaine, marijuana, and methamphetamine.

A young person’s recovery process from stroke differs from an older person’s recovery. While younger adults may be able to bounce back from a stroke better in the long term, they may face greater danger in the short term.

Because the human brain shrinks with age, a younger person has less room in the skull to accommodate the swelling of the brain that can result from a stroke. That means surgeons may have to remove a part of the patient’s skull and keep it off for weeks.

But once the patient is out of those woods, the brains of younger people are a little more resilient. That is particularly true in children. When young children have strokes — usually due to a congenital condition or trauma — their brains can compensate for the damage by retraining new areas adjacent to the injured segment.

While it’s still unclear what exactly is happening in the younger demographic, it’s clear that certain communities are more prone to stroke.

According to the National Stroke Association, African-Americans are twice as likely to die from stroke as Caucasians and Hispanics are more likely to experience strokes at a younger age. Native Americans are also much more prone to the illness.

Read More: Exercise Helps Young Teens Lower Diabetes Risk »

Genetics, Geography, Socioeconomics

Genetics may play a role, too. For example, sickle cell disease is more common in African-Americans and is a high risk factor for stroke.

But socioeconomic reasons such as delayed access to health care and limited healthy food options are probable explanations as well.

Even geography plays a role. The southeastern United States has earned the nickname “the stroke belt” because of how prevalent the condition is there compared with other parts of the country.

While acknowledging that more research is required to understand trends in the younger demographic, George sees these studies as a “wake up call” for young people.

George said lifestyle changes like eating a diet rich in fruits and vegetables, exercising regularly, not smoking, keeping track of blood pressure, and taking medications correctly can lower an individual’s risk of stroke or prevent one altogether.

“Stroke is largely preventable,” she said.