Around one in a hundred deaths worldwide is due to passive smoking, which kills an estimated 600,000 people a year, World Health Organization (WHO) researchers said on Friday.

世界卫生组织的研究人员周五称，全球每100例死亡中就有1例是死于被动吸烟，每年全球约有60万人死于二手烟。

In the first study to assess the global impact of second-hand¹ smoke, WHO experts found that children are more heavily exposed to second-hand smoke than any other age-group, and around 165,000 of them a year die because of it.

"Two-thirds of these deaths occur in Africa and South Asia," the researchers, led by Annette Pruss-Ustun of the WHO in Geneva, wrote in their study.

Children's exposure to second-hand smoke is most likely to happen at home, and the double blow of infectious diseases and tobacco "seems to be a deadly combination for children in these regions", they said.

Commenting on the findings in the Lancet journal, Heather Wipfli and Jonathan Samet from the University of Southern California said policymakers try to motivate families to stop smoking in the home.

"In some countries, smoke-free homes are becoming the norm, but far from universally," they wrote.

The WHO researchers looked at data from 192 countries for their study. To get comprehensive（综合的，广泛的） data from all 192, they had to go back to 2004. They used mathematical modeling to estimate deaths.

Worldwide, 40 percent of children, 33 percent of non-smoking men and 35 percent non-smoking women were exposed to second-hand smoke in 2004, they found.

This exposure was estimated to have caused 379,000 deaths from heart disease, 165,000 from lower respiratory（呼吸的） infections, 36,900 from asthma²（哮喘） and 21,400 from lung cancer.

For the full impact of smoking, these deaths should be added to the estimated 5.1 million deaths a year attributable to active tobacco use, the researchers said.

While deaths due to passive smoking in children were skewed（歪斜的，曲解的） toward poor and middle-income countries, deaths in adults were spread across countries at all income levels.

In Europe's high-income countries, only 71 child deaths occurred, while 35,388 deaths were in adults. Yet in the countries assessed in Africa, an estimated 43,375 deaths due to passive smoking were in children compared with 9,514 in adults.