By AMERICAN HEART ASSOCIATION NEWS

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Traveling to hospitals in the United States is difficult for Yomi Ogun, M.D., a stroke researcher from Nigeria.

A clot-busting medicine to treat stroke is always in stock. In his native country, it’s a rare commodity. Ambulances in America can get patients to hospitals quickly, an underappreciated result of good roads. In Nigeria, Ogun said, stroke victims often die before reaching the hospital.

But although the care of stroke patients clearly differs, Ogun has noticed similarities in how stroke risk affects African-Americans and sub-Saharan Africans from countries such as Nigeria, Ghana and Cameroon.

More than two-thirds of African-Americans can trace their ancestry to those countries and others in the region. It will take collaboration between researchers in Africa and the United States to better understand how stroke and its risk factors affect their populations, Ogun said.

“You compare, you contrast, see areas of similarities, areas of differences — and then see how [to] improve,” said Ogun, a professor of neurology and internal medicine at the College of Medicine at Lagos State University.

The same could be said of studying stroke in Latin Americans and the nearly 57 million U.S. Hispanics.

Mexican neurologist Antonio Arauz, M.D., Ph.D., said considering that most strokes are preventable, U.S. and Latin American researchers must team up to figure out how behaviors, social dynamics and living conditions play a role in risk factors such as high blood pressure, diabetes and high cholesterol. Such insights could lead to more effective prevention strategies to reduce stroke rates.

“A Mexican in the United States… doesn’t have the same eating habits as he does in Mexico City or his place of origin,” said Arauz, a doctor and researcher at the National Institute of Neurology and Neurosurgery Manuel Velasco Suárez in the Mexican capital.

But although lifestyles may differ dramatically, what groups still have in common is genetics. A shared ancestry for populations living different lives in different countries may offer the most valuable clues to preventing strokes — both the United States and abroad.

Such investigations could help determine, for example, whether black Americans are genetically predisposed to strokes, said vascular neurologist Bruce Ovbiagele, M.D., chair of neurology at the Medical University of South Carolina.

“Even after we account for higher rates of diabetes or hypertension, even after we account for lower socioeconomic status for African-Americans, there’s still about a 30 percent higher risk of stroke [compared to U.S. whites that] we still can’t explain,” Ovbiagele said.

Studies could also help researchers understand how acculturation affects the health of immigrants compared to that of their U.S.-born children and grandchildren, said Jose G. Romano, M.D., a professor and stroke division chief in the department of neurology at the University of Miami Miller School of Medicine.

Stroke is the nation’s No. 5 killer and is a leading cause of disability. Worldwide, stroke is the second-leading cause of death. Estimates from the World Health Organization show the burden of death and disability from stroke is seven times higher in low- and middle-income countries, such as Nigeria and Mexico, than in high-income countries, such as the United States and Germany.

In the United States, stroke prevalence is higher among African-Americans than among whites and Hispanics. Yet both African-Americans and Hispanic-Americans face a greater burden of risk factors for stroke: They are more likely to have diabetes, obesity and uncontrolled high blood pressure compared to whites.

According to the Centers for Disease Control and Prevention, stroke is a top killer among Hispanic-Americans and African-Americans, ranking at No. 4 and No. 3, respectively. By comparison, stroke is the No. 5 cause of death for Americans overall.

Plus, statistics from the American Heart Association show African-Americans — the country’s second-largest racial group — are nearly twice as likely to have a first stroke and are about 30 percent to 60 percent more likely to die from a stroke compared to white Americans. Yet Hispanic-Americans are less likely than both black and white Americans to die from a stroke.

But seeing how U.S. data aligns with the experience of sub-Saharan Africans and Latin Americans presents a challenge, experts say, because reliable statistics are hard to come by.

For years, Ovbiagele said, researchers in Nigeria used data from a 1970s-era population study to estimate present-day stroke statistics. In Latin America, researchers long relied on statistics of U.S. Hispanics to calculate figures in their own countries, Arauz said.

Better, more current local data is now available, both experts said, but it is mostly from patient hospital records and doesn’t accurately reflect a country’s overall population.

Ovbiagele and his colleagues recently analyzed strokes in nearly 2,000 native Africans, African-Americans and European-Americans. The findings, published last month in Stroke, suggest race plays a role in the predisposition of certain risk factors for stroke, and possibly even the type of stroke.

Diabetes was more common among native African and African-American stroke patients compared to European-American patients. And nearly all — 93 percent — of native Africans had high blood pressure, as did 83 percent of African-Americans. Among European-American patients, 64 percent had high blood pressure.

The study also showed that hemorrhagic stroke — a type of stroke that causes bleeding in the brain and is strongly linked to high blood pressure — was much more common among native Africans than African-Americans.

“The nature of how you prevent strokes, the emphasis of that, should probably be a little bit different [for native Africans versus African-Americans versus European-Americans],” Ovbiagele said.

Even among U.S. Hispanic ethnic groups, a one-size-fits-all approach to preventing strokes may not be the best approach given that stroke and some of its risk factors appear to impact groups differently. For example, a 2016 CDC report found Puerto Ricans were more likely to report multiple chronic conditions such as stroke, high blood pressure or diabetes compared to people of Mexican, Cuban and Central American descent. Other research has reported that diabetes is more common among Mexican-Americans and Puerto Ricans — the two largest U.S. Hispanic ethnic groups — compared to Hispanics of Cuban and South American heritage.

“Although there are genetic factors involved in disparities, we believe the predominant factor in disparities is access to and use of health care, in large part mediated by socioeconomic factors,” said Romano, a co-investigator of the Florida-Puerto Rico Collaboration to Reduce Stroke Disparities project.

In Latin America, researchers have observed that high blood pressure is more common among Venezuelans, Chileans and Argentinians, and diabetes is more common among people from Mexico, Ecuador, Colombia and Chile.

Partnerships have already developed between U.S. researchers and international colleagues. Ovbiagele said the Medical University of South Carolina has ongoing projects in Nigeria and Ghana. Arauz and Romano recently worked together on a study comparing risk factors in stroke patients in Mexico City and Miami. But the researchers said collaborations between U.S. and Latin American scientists tend to be between scientists and not institutions.

The biggest hurdle researchers now face is money. Funding for international projects is hard to come by, said Ovbiagele.

But that hasn’t deterred Ogun, who feels a sense of urgency. His mother and a brother died from stroke, and another brother recently had one. Researchers worldwide have an obligation to share experiences, he said.

“If we don’t document all that we’re seeing now, how will those that come after us? What will they fall back on?” Ogun said. “We need to do research across the board. It cannot be unilateral.”