Overweight teen boys have higher risk of heart muscle damage

Men who were overweight as teens may be more likely to develop a rare type of heart muscle damage that can cause heart failure than men who maintained a healthy weight during adolescence, a Swedish study suggests.

Researchers examined data on height, weight and fitness levels from more than 1.6 million men who enlisted in compulsory military service in Sweden between 1969 and 2005, when they were 18 or 19 years old. At the start, about 10 percent were overweight and about 2 percent were obese.

After a median follow-up of 27 years, 4,477 men developed a disease called cardiomyopathy that makes it harder for the heart to pump blood to the body. This can lead to heart failure.

Compared to men whose weight was right in the middle of a healthy range in adolescence, men who had a healthy weight that was slightly higher during their teen years were 38 percent more likely to develop cardiomyopathy, the study found. Men who were overweight as teens were at least twice as likely to develop this heart muscle damage, and men who were obese had at least five times the risk.

Men who developed cardiomyopathy were about 46 years old on average at the time of their disorder.

“We postulated that the increase in heart failure rates in the young might be due to increasing rates of overweight and obesity,” said senior study author Dr. Annika Rosengren of the Sahlgrenska Academy and the University of Gothenburg in Sweden.

“We were able to demonstrate that there was a very strong link between being obese when young and early heart failure,” Rosengren said by email.

Cardiomyopathy is still rare, and only 0.27 percent of the men were diagnosed with any one of the different forms of this disorder during the study.

People with a body mass index (BMI) below 20, lean but within a healthy weight range, had a low risk of cardiomyopathy, researchers report in Circulation.

However, that risk steadily increased as weight increased, even among men on the high end of what’s considered a healthy weight, with BMIs ranging from 22.5 to 25.

There are several types of cardiomyopathy, but the causes are poorly understood. In one form, called dilated cardiomyopathy, the heart muscle becomes weak and can’t pump blood efficiently. In another, called hypertrophic cardiomyopathy, the heart muscle becomes stiff and the heart can’t fill with blood properly.

In the study, men who were extremely obese with a BMI of 35 and over in their youth were eight times more likely to develop dilated cardiomyopathy as adults compared to men who were lean in their youth. It was not possible to estimate increased risk for hypertrophic cardiomyopathy in men with BMI 35 and above because there were too few cases to provide a meaningful analysis.

The study wasn’t designed to prove whether or how obesity directly causes cardiomyopathy. It’s also not clear if results from this study of predominantly white men would apply to women or to other racial or ethnic groups.

It’s possible that hormonal and metabolic changes in obesity, including high levels of the hormones insulin and leptin, could play a role in causing cardiomyopathy, said Dr. David Ludwig of Harvard Medical School and Boston Children’s Hospital.

“Exposure to high levels of these two hormones, for years or decades, could adversely affect heart muscle structure and function,” Ludwig, who wasn’t involved in the study, said by email. “It’s also possible that other more commonly recognized changes in obesity, such as high blood pressure and high blood sugar, could be involved.”

Broadly speaking, being overweight or obese as a teen and young adult sets people up for more health issues later in life, heart problems included, said Dr. June Tester of the University of California San Francisco Benioff Children’s Hospital Oakland.

“There are some health complications such as cardiomyopathy that evidence has long suggested that some people are simply more `hard-wired’ than others to have risk just because of their genes,” Tester, who wasn’t involved in the study, said by email. “However, this research suggests that the relationship is more complex.”