Regular exposure to passive smoking increases risk of dying from various causes, finds a new study.
Researchers of the long-term study from China found that compared with adults who lived and worked in smoke-free environs, those exposed to secondhand smoke were more likely to die of heart disease or lung cancer over 17 years.
They were also more likely to die of stroke or the lung disease emphysema-two diseases that have had relatively weaker links to secondhand smoke.
The findings cannot definitively prove that secondhand smoke is the culprit, but the researchers were able to account for some other key factors, like a person's age, education, job, and blood pressure and cholesterol levels.
Additionally, the links between secondhand smoke and mortality remained, say the researchers, led by Dr. Yao He of Chinese PLA General Hospital in Beijing.
"This is exactly the type of study design you want to see," Fox News quoted Joanna Cohen, director of the Institute for Global Tobacco Control at Johns Hopkins Bloomberg School of Public Health in Baltimore.
Cohen, who was not involved in the research, pointed out that the study followed people over many years, and it found evidence of a "dose-response" relationship-meaning people's risks climbed as their secondhand smoke exposure increased.
Those things are considered key in building the case for a cause-and-effect relationship.
A number of studies have found that non-smokers who regularly breathe in other people's tobacco smoke have an increased risk of developing heart disease or certain cancers, including lung tumors.
In the U.S., the most recent Surgeon General's report said there was "suggestive" evidence that secondhand smoke might boost people's risk of stroke and emphysema, also known as chronic obstructive pulmonary disease or COPD.
However, the evidence was considered insufficient to say there was a "causal relationship", Cohen noted.
"This type of study is important for adding to evidence of a causal relationship," she said.
The current findings are based on 910 adults who were followed over almost two decades.
At the start, 44 percent said they lived with a smoker, while 53 percent said they inhaled secondhand smoke at work.
Over the following years, 249 study participants died. And the risks of death from heart disease, stroke, lung cancer and emphysema were all two to three times higher among people exposed to secondhand smoke.
The numbers of people who died of each specific cause were fairly small, which is a limitation.
"When numbers get small it makes it more difficult to get a precise estimate," she said.
But she said the results do support evidence that secondhand smoke may boost the risks of not only heart disease and certain cancers, but stroke and emphysema as well.
The study will be published in the journal Chest.