Michael Brown, Trayvon Martin and Eric Garner are among the unarmed black Americans killed by police over the last several years. These high-profile cases have an effect that goes beyond the victim’s friends and loved ones and even beyond the civil unrest that they inspire. These incidents take their toll on the mental health of all African-Americans, a University of Pennsylvania study has found.

As the demonstrations that have accompanied the shootings make clear, the black community is deeply affected by the violence, Atheendar Venkataramani, co-lead author on the study, told TheDoctor. This is the experience they live with. “What was striking was how big the mental health burden was,” Venkataramani added. The researchers estimated the mental health burden is similar to that caused by diabetes, which affects one in five black Americans.

Almost 49 percent of the African-Americans surveyed had one or more unarmed black Americans killed in their state during the previous three months.

The other finding that surprised the investigators was how specific the effect was. Police killings of unarmed black Americans only affected the mental health of black Americans. This finding suggested to the researchers that black Americans were taking these events in the context of their history.

“Police killings of unarmed black Americans call attention to discrimination against, and a long history of violence against black Americans,” said Venkataramani, an assistant professor of health policy at the University of Pennsylvania. Some of this violence was state-sanctioned, and much of it goes back centuries.

The researchers combined data from police killings that took place between 2013 and 2016 from the Mapping Police Violence database with data from the U.S. Behavioral Risk Factor Surveillance System (BRFSS) survey of more than 103,000 black Americans, aged 18 years or older.

They looked at how many police killings of unarmed African-Americans had taken place in each state where participants lived during the three months before the BRFSS interview. The researchers asked participants to estimate the number of days in the previous month they would rate their mental health as “not good.” They then compared the number of poor mental health days reported by black Americans in the months after a police killing to that of black Americans living in the same state before the event.

They found that almost 40,000 (about 49 percent) of black Americans surveyed had one or more unarmed black Americans killed in their state during the previous three months. Each additional police killing was associated with 0.14 additional poor mental health days among respondents, or about 55 million additional poor mental health days per year among black Americans. The largest effects on mental health were seen one or two months after an incident in which an unarmed African-American was shot by police.

“These findings show how powerful structural racism, or policies entrenched in institutions that harm a particular racial group, can be in influencing peoples’ health,” Venkataramani said. In the future the team hopes to focus on the effects of police killings of unarmed black Americans on physical health, as well as the long-term effects the shootings may have on children.

The study is published in The Lancet.