JOHN YANG: As we've reported recently, life expectancy in the United States is now at its lowest level in nearly two decades, and the projected lifetimes of black and Native Americans are shorter than for white Americans.

New research offers an insight on a potential factor driving this disparity, it finds that black people live longer in areas with more black primary care doctors.

Michael Dill is one of the authors of the study.

He's the Director of Workforce Studies at the Association of American Medical Colleges, which represents medical schools and training hospitals.

How big a benefit or how big a difference is there between life expectancy for black Americans in a county with no black physicians and in counties with at least one black physician?

MICHAEL DILL, Association of American Medical Colleges: Well, John, what we found is that for every 10% increase in the relative Representation of Black primary care physicians, we saw a one month increase in life expectancy for black people living in those same counties.

JOHN YANG: They don't even have to be the patient of the black physician?

MICHAEL DILL: That's right.

We weren't looking at whether or not those black primary care doctors were seeing the black people in the county.

It's just if they're in the same county.

JOHN YANG: This was a correlation rather than cause and effect.

But do you have any theories as to why this is?

MICHAEL DILL: Well, there are any number of explanations.

Part of it is that, you know, black primary care physicians and black physicians in general are more likely to work in underserved areas.

And it was in the lowest income areas where we saw the biggest difference in life expectancy.

And part of it is also that it improves provider choice.

There's also some research to show that, you know, community level access improves with a more diverse workforce.

In fact, our research shows exactly that.

For example, my own primary care physician who's a black woman set up a practice in an area that was very diverse, specifically because she wanted to improve access in that community.

And I think we're seeing some of that in our findings.

JOHN YANG: I was also interested to note that as you began this research, you knocked out half the counties in America, because they don't even have a single black primary care physician?

MICHAEL DILL: That's true, that's true.

There are a couple of explanations for that.

But overall, it is worth noting simply because we don't have enough black primary care physicians or even enough black doctors, not nearly enough.

I mean, the physician workforce overall in the United States has maybe about 6% black physicians, whereas we know the population as a whole is more than twice that.

So and there are also of course, some counties where there just aren't very many people.

So that's part of it too, to be completely transparent about what we were seeing.

JOHN YANG: How can you get more black people to get into the medical field, to be a physician?

MICHAEL DILL: There are multi layered barriers to black people entering the field of medicine, and we need to address all of those.

Our own member institutions are constantly working on improving, you know, their admissions processes using more holistic admission, et cetera.

But they also run what we call pathway programs designed to introduce undergraduate students to the possibility of practicing medicine.

But the issue goes back further than that, it goes to, you know, high school, middle school, primary education levels, even pre-K really in terms of the educational pathway.

And we're focused right now at AMC in particular, looking at K through 12, and STEM education, and enhancing and supporting that in any way we can, because it really is a long-term endeavor to improve the representation of black people and other historically excluded groups in the field of medicine.

JOHN YANG: As they say, there was no cause and effect in this study.

It was a correlation.

But what lessons do you think the medical profession or public health experts should be drawing for this?

MICHAEL DILL: I would say that there are three main lessons to be learned.

One is that just overall, an adequate number of physicians is crucial to the health of all.

Two is that a robust primary care workforce, it's important for population health.

And three is that diversity, and within the physician workforce in the health workforce overall, is in everyone's best interest.

JOHN YANG: Michael Dell of the Association of American Medical Colleges, thank you very much.

MICHAEL DILL: Thank you.