(CNN) — The Covid-19 pandemic set US life expectancy back by years, but new research shows that the country has been falling behind for decades.

In 1950, the US had the 12th longest life expectancy among certain populous countries, with more than half a million residents, according to a study published Thursday in the American Journal of Public Health. There was a 3.5-year difference between the US and Norway, which had the longest life expectancy at the time.

By 2019, the life expectancy gap between the US and the highest-performing nation – now Hong Kong – had grown to more than six years, putting the US in 40th place among populous countries.

The Covid-19 pandemic widened that gap even more, as the US had more deaths from the virus than any other country and has been slower to recover. In 2020, the US ranked 46th and had a 7.8-year gap from the highest-performing nation, according to the study. Life expectancy was 77.4 years in the US that year, compared with 85.2 years in Hong Kong, according to data from the United Nations.

Life expectancy is a “summary measure of our health,” said study author Dr. Steven Woolf, director emeritus of the Virginia Commonwealth University Center on Society and Health. It’s not the only way to gauge the quality of life in a particular place, but it does tend to mirror trends in other health-related metrics, he said.

For these measures, the US is often compared with other wealthy and highly-industrialized nations that are considered to be its peers.

But this report shows that a diverse group of countries across six continents and a range of economic conditions have surpassed the US on life expectancy. Among the countries that have surpassed the US in recent years are Albania, a former member of the Eastern Bloc, and Lebanon.

“The premise is shifting,” Woolf said.

The US “life expectancy disadvantage” has steadily worsened since 1950, according to the new study, and Woolf groups the trend into six phases. There were some years of growth and rebound, but more often than not, the pace of increase for the US lagged behind that of other countries. Overall, the US had smaller annual increases in life expectancy than other populous countries, on average, in 49 of the 70 years studied.

A plateau in the 2010s led to a “dramatically” wider gap for the US, and the Covid-19 years were “simply phase six of something that has been going on since the 1950s,” Woolf said.

“The pandemic was horrific loss of life, but it really reflects pre-existing, systemic problems in our country that have been compromising the health of Americans for decades.”

A decade ago, a group of researchers set out to identify the specific factors that were holding the US back from achieving the same gains in life expectancy as other countries. The report from the National Research Council Institute of Medicine focused on five key areas: health care, health behaviors, social and economic factors, environment and public policy.

“We hoped that there would be an answer in one of those that would sort of be a magic bullet. But in every single one of those categories, we found dramatic differences between the US and other countries,” Woolf said – and things have only gotten worse since.

For example, the US lacks universal health care and has higher caloric intake, more guns, more drugs and higher rates of child poverty, among other differences.

Within the US, Woolf found in his new research that life expectancy grew slowest in the Midwest and South Central regions.

Many of the complex factors that drive life expectancy changes are as different among US states as they are among countries.

Some regions in the US experienced “tectonic shifts” in their economy and population demographics during the years when life expectancy started changing, such as the collapse of the manufacturing sector that hit the Midwest particularly hard, Woolf said.

Much more research is needed to understand exactly what is driving the gaps within the US, he said. But state-level policy decisions are a major factor.

“There are a variety of state-level policy decisions that seem to be strongly correlated with the life expectancy trends that we’ve seen,” Woolf said.

And that link may become more apparent as states continue to exert their authority.

“We saw states become really important during the pandemic. And then as we’ve exited the pandemic, we’re now seeing states be extremely active on issues like abortion and reproductive health rights, gun control and a variety of issues that are going to continue to demonstrate this same pattern,” he said.

“Health outcomes at the state level are likely going to diverge more, given the direction we’re taking.”

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