Even though diabetes rates are almost twice as high in black people as in whites, black patients may be far less likely to be included in drug safety trials, a recent study suggests.

Since 2008, the U.S. Food and Drug Administration has required that new glucose-lowering medications for diabetes be tested for cardiovascular safety, which may differ based on patients' race or ethnicity, researchers note in The Lancet Diabetes and Endocrinology.

When researchers looked at seven diabetes drug trials done since then to test cardiovascular safety, they found that in five of the trials, black people made up less than 5 percent of the patients.

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"In the United States the burden of diabetes and the serious complications associated with it fall unfairly on minorities, particularly African Americans, yet it appears that they are under-represented in clinical trials of new therapies and devices," said study co-author Dr. David Kerr of the William Sansum Diabetes Center in Santa Barbara, California.

"If they are excluded they may be exposed to therapies which may not work or could cause harm," Kerr added by email. "The therapies are also likely to be expensive and ineffective."

About 13 percent of black people in the U.S. have diabetes, compared with 7.6 percent of white Americans.

Death rates from cardiovascular disease are also disproportionately high among black Americans, the researchers point out.

When it comes to drug effectiveness and safety, self-identified race doesn't necessarily predict response to a treatment or suggest that outcomes would be similar among patients of different races.

Still, the majority of cardiovascular studies in recent decades have focused on white heterosexual males, noted Dr. Andrew Krumerman, of Albert Einstein College of Medicine and Montefiore Medical Center in New York.

"The current study confirms the notion that African American subjects are poorly represented in large cardiovascular outcome trials," Krumerman, who wasn't involved in the study, added by email.

When drug trial participation isn't balanced across gender, race, ethnicity and socioeconomic status, it can be easy to miss critical distinctions in how treatments may work in different types of people, said Dr. Keith Ferdinand, of Tulane School of Medicine in New Orleans. "Certain groups of patients may respond differently to the same therapies."

There are examples beyond just diabetes. For example, studies have found two types of blood pressure drugs don't work as well in black patients as other people, and one medicine for heart failure works very well in black patients but not in white patients, Ferdinand, who wasn't involved in the study, said by email.

"For some time we have known high risk minority populations have been underrepresented in clinical trials," said Dr. Daniel Lackland, a researcher at Medical University of South Carolina who wasn't involved in the study.

"This major issue is not limited to diabetes studies but also cancer and other clinical trials," Lackland added by email.