Black people in counties with more Black primary care physicians live longer, according to a new national analysis that provides the strongest evidence yet that increasing the diversity of the medical workforce may be key to ending deeply entrenched racial health disparities.

The study, published Friday in JAMA Network Open, is the first to link a higher prevalence of Black doctors to longer life expectancy and lower mortality in Black populations. Other studies have shown that when Black patients are treated by Black doctors, they are more satisfied with their health care, more likely to have received the preventive care they needed in the past year, and are more likely to agree to recommended preventive care such as blood tests and flu shots. But none of that research has shown an impact on Black life expectancy.

The new study found that Black residents in counties with more Black physicians — whether or not they actually see those doctors — had lower mortality from all causes, and showed that these counties had lower disparities in mortality rates between Black and white residents. The finding of longer life expectancy persisted even in counties with a single Black physician.