African Americans are systematically under-treated for pain when compared to whites, research shows, and a new study suggests that doctors' racial bias may be -- at least in part -- to blame.

Researchers from the University of Virginia surveyed over 200 white medical students and residents on their beliefs about biological differences between black and white people that could affect how they assess and treat the pain experienced by black patients.

The participants were asked such questions as: Are black people's nerve endings less sensitive than white people's nerve endings? Do blacks have thicker skin than whites? Do black people's blood coagulate more quickly than whites'?

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The results, published the journal Proceedings of the National Academy of Sciences, showed that many of the medical students and new doctors hold these beliefs, most likely affecting their treatment decisions.

"Many previous studies have shown that black Americans are under-treated for pain compared to white Americans, because physicians might assume black patients might abuse the medications or because they might not recognize the pain of their black patients in the first place," Kelly Hoffman, a UVA psychology Ph.D. candidate who led the study, said in a statement. "Our findings show that beliefs about black-white differences in biology may contribute to this disparity."

Specifically, about 40 percent of first and second year medical students, 22 percent of third year medical students, and 25 percent of residents reported believing that blacks' skin is thicker than whites'. Twenty-nine percent of first year medical students, 17 percent of second year students, 3 percent of third year students, and 4 percent of residents believe black people's blood coagulates more quickly than whites'.

The researchers also asked about the participants' beliefs on true statements on biological differences between the races, such as: whites are less susceptible to heart disease and whites are less likely to have a stroke than blacks. Many of those surveyed did not believe these statements to be true.

Additionally, Hoffman and her team asked the subjects to rate on a scale of zero to 10 the pain levels they would associate with two mock medical cases -- a kidney stone and a leg fracture -- for both a white and a black patient. They were then told to recommend treatments based on the level of pain they thought the patients might be experiencing.

The study showed that half of the medical students and new doctors endorsed at least one of the false beliefs and these individuals were more likely report lower pain ratings for the black compared to the white patient. Furthermore, they were also less likely to recommend accurate treatment for the black patient versus the white patient.

To verify treatment accuracy, the researchers provided 10 experienced physicians with the same medical cases. The majority recommended a narcotic for both cases, which also aligns with the pain treatment recommendations of the World Health Organization.

"We've known for a long time that there are huge disparities in how blacks and whites are assessed and treated by the medical community," Hoffman said. "Our study provides some insight to what might contribute to this -- false beliefs about biological differences between blacks and whites. These beliefs have been around for a long time in our history. They were once used to justify slavery and the inhumane treatment of black people in medicine."

The study authors note that, importantly, white medical students and residents who did not endorse these false beliefs did not show the same bias as their counterparts. They said future research should focus on whether challenging these beliefs could lead to better treatment and outcomes for black patients.