A common cold bug could cause heart attacks in younger men, U.S. researchers reported on Tuesday.

The findings add to a growing body of evidence that Chlamydia pneumoniae and perhaps other infections can sometimes damage the heart and arteries, causing heart disease.

Christine Arcari and colleagues at the University of Wisconsin Medical School and Johns Hopkins University in Baltimore studied regular blood samples taken from soldiers aged between 30 and 50, identifying 300 of them who suffered Heart attacks.

They compared their blood records to 300 men who had not suffered heart attacks.

Writing in the journal Clinical Infectious Diseases, the researchers said they tested each blood sample for antibodies, which provide indirect evidence of previous infection.

There is no direct test for infection with Chlamydia pneumoniae, a bacterium that causes a flu-like upper respiratory infection that sometimes worsens to pneumonia.

They looked specifically for two antibodies - IgA and IgG - that recognize and attack chlamydia bacteria.

“IgG antibodies are like a long-term memory, while IgA is thought to be a more specific marker for recent or chronic infections,” Arcari said.

Men who had high levels of IgA antibodies were more likely to have had serious heart attacks, they found. And the more recent the infection, the more likely they were to have suffered a Heart attack .

“This indicated the possible importance between the time of infection and the date of the cardiac event,” Arcari said.

Dr. Javier Nieto, chair of the Department of Population Health Sciences at the University of Wisconsin, said it may be difficult to say yet how the findings may be used.

“Since Chlamydia infection is so common, by the time people reach 65 years of age, most will have been exposed to it,” he said. “By looking at infection in younger people, we may be able to identify early stages of atherosclerosis.”

Experts believe that infections may cause inflammation or perhaps an abnormal immune response in some people that damages the heart and arteries.