People who breathe in a lot of other people's tobacco smoke are twice as likely to die from heart disease as those exposed to lower levels of "secondhand" smoke, a new study suggests.

The findings add to the growing body of evidence linking secondhand smoke to cardiovascular disease, Dr. Steven Schroeder, director of the Smoking Cessation Leadership Center at the University of California, San Francisco, who was not involved with the study, told Reuters Health.

In the study, Dr. Mark Hamer of University College London, UK, and colleagues used a saliva test that is able to measure the amount of secondhand smoke people have been exposed to. They gave this test to over 13,000 people in England and Scotland and then followed them for an average of 8 years, keeping track of who developed heart disease and who died.

Over the course of the study, 32 out of about 1,500 people who had never smoked but were exposed to high levels of secondhand smoke died of heart disease, compared to 15 out of about 1,000 "never-smokers" with low exposure.

In analyses restricted to never-smokers, high secondhand smoke exposure was associated with more than a two-fold increased risk of dying from heart disease.

A "high" level of exposure, Hamer explained, would be equivalent to living with a smoker and getting exposed to secondhand smoke pretty much every day. About 1 in 5 of the people in the study had high exposure levels, according to the saliva test.

People exposed to a lot of secondhand smoke, as well as smokers themselves, were younger and more likely to be male, worse off financially, and less physically active than people with low exposure. But even when controlling for these potentially confounding factors, the link between secondhand smoke exposure and heart disease remained.

The study is published in the latest issue of the Journal of the American College of Cardiology.

Hamer's team also found evidence, as have other research teams, that secondhand smoke triggers inflammation in the body, a known risk factor for heart disease.

"Even though the biological mechanisms are not fully understood yet, there's growing evidence that indicates that exposure to fine particles (such as those in cigarette smoke)...results in this low to moderate inflammation," Dr. C. Arden Pope III, an economist and environmental epidemiologist at Brigham Young University in Provo, Utah, told Reuters Health.

Pope, who was not involved in the study, said: "There's a fairly substantial literature now that indicates that secondhand smoke is associated with cardiovascular disease. "This study...certainly contributes to our knowledge."