People regularly exposed to secondhand smoke may have increased risks of dying from various causes, a long-term study from China suggests.

Researchers 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.

And 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, which appear in the medical journal Chest, 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.

And the links between secondhand smoke and mortality remained, say the researchers, led by Dr. Yao He of Chinese PLA General Hospital in Beijing.