Researchers say the likely culprits are obesity and the resulting increase in Type 2 diabetes

After four decades of dramatic progress, the public-health battle in the U.S. against the ravages of heart disease may have hit a wall.

Since 2011, the annual decline in heart-disease death rates among Americans has essentially remained flat at less than 1%, researchers said Wednesday, a contrast to some 40 years of continuous and generally much steeper annual reductions. In the decade ending in 2010, the average annual decline in heart-disease mortality was 3.7%.

The likely culprits, researchers said, are the epidemic of obesity and the resulting increase in prevalence of Type 2 diabetes, both important risk factors for cardiovascular disease. The rise in obesity first emerged across all ages in the U.S. in about 1985 and researchers believe the consequences are now beginning to turn up in mortality data.

“This is a startling observation,” Jamal S. Rana, a cardiologist and researcher at Kaiser Permanente in Oakland, Calif. “Things are slowing down. We need to redouble our efforts” on innovative prevention strategies “to turn the tide,” he said. Dr. Rana is senior author of the study, which was published online Wednesday in JAMA Cardiology, a journal of the American Medical Association.

Cardiovascular disease has been the leading killer of Americans for nearly a century. But since 1970, deaths from heart disease and stroke have dropped more than 70% in the U.S. and most other Western countries, a result of concerted public-health efforts and major medical advances.

Antismoking campaigns, healthier lifestyles, the development of medicines to control blood pressure and cholesterol, and new strategies for treating heart attacks are among key contributors to the decline, researchers say.

Progress was so pronounced in the past decade that by 2010 projections were that cancer would overtake heart disease as the nation’s leading cause of death by 2013. Cardiologists prepared to celebrate a “We’re No. 2” moment, said Donald Lloyd-Jones, head of preventive medicine at Northwestern University’s Feinberg School of Medicine.

But the party never happened. When the cancer deaths didn’t pass heart-disease in 2014, Stephen Sidney, an epidemiologist at Kaiser Permanente who was tracking the trends, decided to take a deeper look.

He and his colleagues at Kaiser Permanente used the U.S. Centers for Disease Control and Prevention’s public-health database called Wonder (for Wide-ranging Online Data for Epidemiological Research), which includes death-certificate data filed in all 50 states and Washington, D.C.

The analysis found the stalling of the death-rate decline for cardiovascular disease and stroke began in 2011 and remained flat through 2014. It occurred across genders and racial and ethnic groups. In addition, death rates from cancer, which had declined on average 1.5% a year between 2000 and 2010, continued to drop at about the same rate through 2014.

Dr. Sidney, who is lead author of study, said a look at some provisional data in the third quarter of 2015 indicated death rates for heart disease and stroke were higher than in 2014. If that were confirmed throughout the full year, “it would mark a potential reversal” of the favorable heart-disease trends, he said.

While the data can’t explain the reasons for the change, Dr. Lloyd-Jones said that “there is every reason to think that obesity is a major driver of what we’re seeing.” About a decade ago, he said, research indicated an increase in heart-disease death rates among young people, likely a harbinger of the new findings. Dr. Lloyd-Jones is author of an editorial accompanying the study but wasn’t involved in the research.

To combat the trends, he said, “we need to use every tool in the toolbox.” That includes continued efforts to eliminate smoking, control blood pressure and cholesterol and to prevent obesity.

The key to long-term sustained progress, he said, is to maintain “healthy weight through childhood and early adulthood,” to prevent risk factors from taking root at a young age. If that happens “these problems will melt away.”

Dr. Lloyd-Jones noted that while the study focuses on death rates, prevention strategies can help reduce the number of people who suffer heart attacks and strokes to begin with. “It would not only improve death rates,” he said. “It would improve the quality of life for millions of Americans.”

This story originally appeared in the Wall Street Journal on June 29, 2016.