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.

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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.

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