Being seriously overweight can lead to prolonged inflammation in the heart that can cause heart disease, finds a large U.S. study.

In a study of 7,000 men and women aged 45 to 84, Johns Hopkins University-affiliated researchers identified 79 who had developed congestive heart failure. Of these participants, 25 of them, or 44 per cent, were obese, having a body mass index of 30 or higher.

The obese patients also had higher levels of interleukin-6, C-reactive protein and fibrinogen — proteins that are involved in inflammation, according to the researchers.

Participants with double the interleukin-6 levels of non-obese adults had an 84 per cent greater risk of developing heart failure during the study period.

If they had triple the average levels of C-reactive protein, they increased their risk of heart failure by 36 per cent, the study found. And as little as one-fifth higher-than-average levels of fibrinogen increased the risk of heart failure by 37 per cent.

"The biological effects of obesity on the heart are quite profound," said senior study investigator Joao Lima, in a release. "Even if obese people feel otherwise healthy, there are measurable and early chemical signs of damage to their heart, beyond the well-known implications for diabetes and high blood pressure."

The researchers also discovered that if a person had a mix of heart disease factors known as metabolic syndrome, such as high blood pressure, high blood sugar, excess abdominal fat and abnormal cholesterol levels and obesity, they had a 50 per cent greater chance of developing the condition than people without these factors.

"The basic evidence is building the case that inflammation may be the chemical route by which obesity targets the heart, and that inflammation may play an important role in the increased risk of heart failure in obese people, especially those with the metabolic syndrome," said lead author Hossein Bahrami.

Lima said that doctors should look for signs of inflammation in patients who are obese to prevent the development of heart disease.

The study's participants will be tracked until 2012. The study started in 2000. It will be published in the May 6 issue of the Journal of the American College of Cardiology.