Around 165,000 children die each year as a result of passive smoking, according to new figures from the World Health Organisation (WHO).
Children accounted for 28 per cent of all deaths from second-hand smoke, while women accounted for 47 per cent of deaths and men 26 per cent.
According to WHO scientists, 603,000 people worldwide die from the effects of passive smoking each year.
Writing in the Lancet medical journal, the study authors explained: "Children's exposure to second-hand smoke most likely happens at home.
"The combination of infectious diseases and tobacco seems to be a deadly combination for children in these regions and might hamper the efforts to reduce the mortality rate for those aged younger than five years, as sought by Millennium Development Goal Four."
Researchers studied data collected from 192 countries in 2004, calculating the number of deaths and years lost of life in good health.
They found that 40 per cent of children, 33 per cent of male non-smokers and 35 per cent of female non-smokers were exposed to second-hand smoke that year.
This exposure is thought to have caused 379,000 deaths from ischaemic heart disease; 165,000 from lower respiratory infections; 36,900 from asthma; and 21,400 from lung cancer.
The WHO study calls for educational strategies to encourage people to stop smoking in their homes and urged developing countries to pay as much attention to tobacco-related diseases as infectious ones.
Robin Hewings, Cancer Research UK's tobacco control manager, said: "This research shows the terrible toll tobacco takes on the health of smokers and non-smokers. Successful campaigns to encourage people not to smoke indoors need to be continued.”
