Immunizations, fluoridated drinking water, the reduction in tobacco use. These are among America’s 10 greatest public-health achievements in the 20th century, according to the Centers for Disease Control. One fix that doesn’t come up often in conversations about improving Americans’ health outcomes? Increasing the number of people who get high-school degrees.

There are lots of well-known benefits associated with higher educational attainment: Graduates earn better incomes, are less likely to end up in jail, and lead healthier lives. The federal government’s Healthy People 2020 agenda, which outlines goals for promoting health and preventing disease, acknowledges this association, setting targets for increasing the percentage of high-school students who graduate on time. There's already a body of research that shows someone without a diploma is more at risk of premature death than someone who does have one.

Until now, however, there has been relatively little known about the proportion of early deaths that can be linked to dropping out.

A new study by researchers at the University of Colorado, New York University, and the University of North Carolina at Chapel Hill may have the answer. The study, which was published Wednesday in the journal PLOS ONE, looked at the relative risk of death among people with various levels of education and compared that with the distribution of educational attainment across the U.S. population. And what the analysis found, said co-researcher Virginia Chang, was “really quite surprising.”

The difference in “the number of deaths that we can attribute to finishing high school or not is on par with the difference between current and former smokers,” said Chang, a public-health professor at NYU who focuses on obesity.

Using survey data from the Centers for Disease Control to assess how education levels affected mortality over time, the researchers concluded that, using the educational disparities observed among people born in 1945, the deaths in 2010 of hundreds of thousands of American adults could have been prevented if those people had gotten high-school or bachelor’s degrees. Specifically, the deaths of roughly 145,000 individuals were associated with those individuals’ failure to get a high-school degree, while the deaths of another 110,000 or so people were attributed to those adults failing to complete their four-year degree programs.

Among those who died early, there were higher rates of cardiovascular disease—a finding that echoes previous studies tracking the correlation between mortality rates and educational attainment. “The trend is best explained by tobacco, obesity, and high blood pressure,” Ahmedin Jemal, an epidemiologist at the American Cancer Society, told The Washington Post about a study that produced similar findings in 2008.

The more recent study found that disparities in mortality rates relative to different levels of education grew significantly over time. Encouraging individuals who haven’t finished high school to get their diplomas (or complete their GEDs), “could save twice as many lives among those born in 1945 as compared to those born in 1925,” the study’s press release says. Deaths from cardiovascular disease played a greater role in these widening education-related mortality gaps than did cancer, a finding the researchers cite as evidence that advances in cardiovascular prevention and treatment options among degree-holding adults played a role. “Unless these trends change, the mortality attributable to low education will continue to increase in the future,” said co-researcher Patrick Krueger, a behavioral-sciences professor at the University of Colorado.

In other words, life expectancy is increasing, “but those with more education are reaping the most benefits,” Chang said.

These findings suggest that public-health efforts in the country today should consider placing a greater emphasis on promoting higher educational attainment—a goal that doesn’t often come up in conversations outside of education circles. Boosting high-school graduation rates has long been the territory of school districts such as Chicago and campaigns like that of GradNation, which have seen significant strides in the last decade: In 2012, more than 80 percent of high-schoolers in the U.S. graduated on time, up 10 percentage points from what it was a decade before that.

Still, that means one in five students in the U.S. does not complete high school on time. According to NYU’s Steinhardt school, more than one out of every 10 adults aged 25 through 34 in the U.S. lacks a high-school degree; more than a quarter don’t have a bachelor’s degree. Perhaps other sectors should be pushing for better graduation rates—and perhaps existing education campaigns should do more to highlight the long-term benefits of getting a diploma, including how closing the achievement gap has to do with much more than achievement alone.

Coincidentally, GradNation released a research brief on Wednesday with findings on what life experiences and risk factors can make a student more likely to drop out of high school. Drawing on a quarter-century of empirical studies, the brief outlines the “assets” that can have the strongest impact on a kid’s decision to stay in school, including parental involvement in academics, participation in extracurriculars, peers’ academic habits, and strong student-teacher relationships. Maybe these are areas people outside of education should be focusing on, too.

“In public health and public-health policy, there is a lot of emphasis on [addressing] health behaviors: smoking, obesity, nutrition, drinking, et cetera,” Chang said. “There should be more attention paid to education, which is a more fundamental driver of these behaviors.”

America’s healthcare system, according to Chang, tends to focus on the “more-proximal causes” of disease. “We try to break things down into all the little pieces along the causal pathways … If someone is dying of lung cancer, we focus on the smoking because that was one of the more proximal events,” she said. “We don’t go more upstream and think about social conditions as fundamental causes of mortality.”