Background:
Prior studies have reported that greater numbers of primary care physicians (PCPs) per population are associated with reduced population mortality, but the effect of increasing PCP density in areas of low density is poorly understood.

Objective:
To estimate how alleviating PCP shortages might change life expectancy and mortality.

Design:
Generalized additive models, mixed-effects models, and generalized estimating equations.

Setting:
3104 U.S. counties from 2010 to 2017.

Participants:
Children and adults.

Measurements:
Age-adjusted life expectancy; all-cause mortality; and mortality due to cardiovascular disease, cancer, infectious disease, respiratory disease, and substance use or injury.

Results:
Persons living in counties with less than 1 physician per 3500 persons in 2017 had a mean life expectancy that was 310.9 days shorter than for persons living in counties above that threshold. In the low-density counties (n = 1218), increasing the density of PCPs above the 1:3500 threshold would be expected to increase mean life expectancy by 22.4 days (median, 19.4 days [95% CI, 0.9 to 45.6 days]), and all such counties would require 17 651 more physicians, or about 14.5 more physicians per shortage county. If counties with less than 1 physician per 1500 persons (n = 2636) were to reach the 1:1500 threshold, life expectancy would be expected to increase by 56.3 days (median, 55.6 days [CI, 4.2 to 105.6 days]), and all such counties would require 95 754 more physicians, or about 36.3 more physicians per shortage county.

Limitation:
Some projections are based on extrapolations of the actual data.

Conclusion:
In counties with fewer PCPs per population, increases in PCP density would be expected to substantially improve life expectancy.

Primary Funding Source:
None.