By Amy Norton
MONDAY, March 21, 2016 (HealthDay News) -- Fewer Americans are dying from heart disease compared with 40 years ago, but not all parts of the country are showing the same downward trend, a new federal government study finds.
Researchers say the nation's heart-disease hotbeds have largely migrated south. In the 1970s, U.S. counties with the highest death rates from heart disease were clustered in the Northeast; now they are concentrated in Southern states, especially the deep South.
The study, published March 22 in the journal Circulation, can only show the trend -- and not the reasons for it, said lead researcher Michele Casper.
"But from other studies we know the socioeconomic conditions of a county can affect rates of smoking and obesity, or whether people have access to affordable, healthy food, for example," said Casper, an epidemiologist at the U.S. Centers for Disease Control and Prevention.
According to Dr. Donald Barr, a professor at Stanford University School of Medicine in California, the issue is clearly social.
Southern states, he said, often have higher rates of obesity, type 2 diabetes and kidney disease, which are risk factors for heart disease. And social conditions -- from poverty and low education levels, to racial injustice -- are at the root of the problem, Barr said.
"Social risk factors for heart disease are more common in the South," he said. "This disparity [in heart disease deaths] is not about hospital care. It's about broader social structure."
For the study, Casper's team looked at U.S. counties' rates of death from heart disease between 1973 and 2010. Nationwide, the researchers found, those deaths fell by about 62 percent.
But counties varied widely, the study found. In counties with the smallest improvements, heart disease deaths fell by anywhere from 9 percent to 50 percent. And those counties were concentrated in Alabama, Arkansas, Louisiana, Mississippi, Oklahoma and parts of Texas.
In contrast, counties with the greatest improvements saw death rates drop between 64 percent and 83 percent -- and they were mostly in the North.
In the early 1970s, almost half of counties in the Northeast were considered to have high rates of death from heart disease, versus the rest of the country. By 2010, that had plummeted to just 4 percent of Northeastern counties.
The South, however, has seen the opposite trend. In 2010, 38 percent of the region's counties had high death rates from heart disease, versus 24 percent in the 1970s.
Like the Northeast, the Midwest showed a decline in counties with high heart disease death rates. In 2010, 6 percent of its counties fell into that category. The West had, by far, the lowest death rates in the 1970s, and it's still home to most of the nation's "low-rate clusters," the study found.
"We observed the north-south shift over a relatively short period of time," Casper pointed out. "So something powerful is going on."
The hope, she said, is that counties and communities can use this information to "look at local factors" that could affect heart disease rates.
Americans can take steps to lower their heart disease risk, Casper noted -- by eating a healthy diet, getting regular exercise and not smoking. But, she added, they also need help in doing those things.
"It really takes a collective effort," Casper said. "People need access to healthy food and safe places to exercise."
Barr said other research points to a shift in the type of heart disease that's killing Americans these days. Heart disease, he explained, includes coronary heart disease, where fatty plaques build up in the heart arteries and can eventually cause a heart attack.
But there is also heart failure -- a chronic disease where the heart muscle loses its ability to pump blood efficiently enough to meet the body's needs.
Declines in smoking and uncontrolled high cholesterol have helped cut coronary heart disease deaths, Barr said. But, he added, research shows that obesity, diabetes and high blood pressure seem to be feeding more heart failure cases -- particularly among blacks.
"I think the geographic shift in death rates is also reflecting a shift from coronary heart disease to heart failure," Barr said.
The only way to change those regional patterns, he said, is by addressing the underlying social issues.