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, according to a British study.
The findings, which add to the growing body of evidence linking secondhand smoke to cardiovascular disease, came from a study by University College London of more then 13,000 people in England and Scotland.
Researchers used a saliva test that can measure the amount of secondhand smoke people have been exposed to and followed the group 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.
Researcher Dr. Mark Hamer said analyses restricted to never-smokers found that 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.