Secondhand smoke is estimated to cause more than 600,000 deaths a year worldwide, 165,000 of them among children younger than 5, according to a World Health Organisation research group.
The group urged policymakers to immediately enforce the global body's framework convention on tobacco control to create smoke-free environments in all indoor workplaces as well as in public places and on public transport.
The study, which the group claims is the first global estimate of deaths from the exposure to secondhand smoke, was recently released in British medical journal The Lancet.
Analysing data from 192 countries, the group found that 40 per cent of children younger than 15, 35 per cent of female nonsmokers and 33 per cent of male nonsmokers were exposed to secondhand smoke worldwide in 2004.
This exposure led to heart disease, respiratory infections, asthma and lung cancer, resulting in 603,000 deaths that year, accounting for about 1.0 per cent of worldwide deaths, it said.
About 60 per cent of the 165,000 child deaths occurred in Africa and South Asia. As children's exposure to secondhand smoke most likely happened at home, the combination of infectious diseases and tobacco seems to be a deadly combination for children in these regions, the group said.
Smokers are not only putting themselves at risk, but also the 1.8 billion nonsmokers, the group said, concluding that some 5.7 million deaths per year worldwide are attributable to tobacco including passive smoking, combined with an estimated 5.1 million deaths among smokers due to tobacco-related causes.