In the first study of its kind, researchers from UC Berkeley School of Public Health found that Black workers in Michigan automobile manufacturing plants with a greater number of Black colleagues had better cardiovascular health than Black auto workers who worked in overwhelmingly white plants.

The retrospective cohort study, published online in September ahead of print in the Journal of Epidemiology and Community Health, examined nearly 40,000 auto workers from three Michigan automobile plants.

“Among Black workers, we observed a strong protective association between greater workforce racial diversity and cardiovascular mortality,” the authors wrote. Results among white workers were mixed, with protective health effects in plants with less than 20% Black workers and either no effects, or harmful effects, in the plant with more than 20% Black workers over the follow-up period.

Professor Ellen Eisen, director of Berkeley Public Health’s Occupational and Environmental Epidemiology Training Program, served as senior author on the paper. Although Eisen has spent most of her career studying environmental exposures in the workplace, she has also become interested in considering the workplace as a social determinant of health.

“I’ve started thinking more about the workplace as a social construct, and have studied the health effects of job loss as well as the impacts of racial composition and segregation of the workplace as measures of structural racism,” Eisen said in an interview. “I realized that we had the information to look at changes in racial composition over time, and treat it as a long-term exposure variable—similar to other environmental exposures.”

Study lead author Hilary L. Colbeth was a student of Eisen’s. She received her Ph.D. in epidemiology in May 2024 and is now a postdoctoral scholar at UC Davis.

The researchers developed a quantitative measure of exposure to racial diversity—the percentage of Black workers employed in each plant each year. They then examined the cardiovascular mortality risk of each worker in relation to their average long-term exposure.

“I’ve been following a large population of UAW-GM auto workers for mortality outcomes since the late 1980s,” Eisen said. “The workforce was largely a white male population, with a growing number of Black workers over time.”

The researchers leveraged longitudinal data from this cohort mortality study of hourly automobile workers in Detroit, Ypsilanti, and Saginaw, Michigan, from 1941 to 2015. The data included the percentage of white and Black workers at each facility in each year and cardiovascular deaths.

“Our results are consistent with literature documenting that social environmental indicators of support may have a strong effect on cardiovascular health in Black cohorts,” Colbeth said.

“In the Detroit plant, white GM workers were no longer the majority after 1967. Research suggests that white workers in a majority non-white work environment may experience heightened anxiety or status threat because they are unused to occupying a numeric minority status.”

The authors advocate the development of interventions focused on workplace policies and practices to encourage social support, representation, and inclusivity to reduce harm from racial exclusions.