Exposure to passive smoking in childhood causes irreversible damage to the structure of children's arteries, scientists have warned.
The thickening of the arteries' walls associated with being exposed to parents' smoke, means that these children will be at greater risk of heart attacks and strokes in later life, researchers said.
The researchers from Tasmania, Australia and Finland said that exposure to both parents smoking in childhood adds an extra 3.3 years to the age of blood vessels when the children reach adulthood.
The study is the first to follow children through to adulthood in order to examine the association between exposure to parental smoking and increased carotid intima-media thickness (IMT) - a measurement of the thickness of the innermost two layers of the arterial wall - in adulthood.
The study was made up of 2,401 participants in the Cardiovascular Risk in Young Finns Study, which started in 1980, and 1,375 participants in the Childhood Determinants of Adult Health study, which started in 1985 in Australia.
The children were aged between three and 18 at the start of the studies. The researchers asked questions about parents' smoking habits and used ultrasound to measure the thickness of the children's artery walls once they reached adulthood.
The researchers found that carotid IMT in adulthood was 0.015 mm thicker in those exposed to both parents smoking than in those whose parents did not smoke, increasing from an average of 0.637 mm to 0.652 mm.
"Our study shows that exposure to passive smoke in childhood causes a direct and irreversible damage to the structure of the arteries," said Dr Seana Gall, a research fellow in cardiovascular epidemiology at the Menzies Research Institute Tasmania and the University of Tasmania.
"While the differences in artery thickness are modest, it is important to consider that they represent the independent effect of a single measure of exposure - that is, whether or not the parents smoked at the start of the studies - some 20 years earlier in a group already at greater risk of heart disease.
"For example, those with both parents smoking were more likely, as adults, to be smokers or overweight than those whose parents didn't smoke," Gall said.
Interestingly, the study did not show an effect if only one parent smoked.
"We think that the effect was only apparent with both parents smoking because of the greater overall dose of smoke these children were exposed to," said Gall.
The study was published in the European Heart Journal.
