Passive smoking causes irreversible damage to the arteries of children and increases their risk of suffering a heart attack or stroke later in life, a new study has revealed.

Scientists in Finland, Australia and Tasmania investigated the link between exposure to parental smoking as a child and increased carotid IMT (intima-media thickness) in adulthood. This is a measurement of the thickness of the two innermost layers of the walls of the arteries.

This marks the first study to investigate this link from childhood through to adulthood.

It looked at over 2,400 young people in Finland who were taking part in a long-term cardiovascular risk study and more than 1,300 young people in Australia taking part in a long-term health study.

Both studies began in the 1980s when the children were aged between three and 18.

Information on parental smoking habits was gathered and ultrasounds were used to measure the thickness of the participants' arterial walls once they had reached adulthood.

The scientists found that carotid IMT was thicker in those exposed to passive smoking as children. They determined that exposure to both parents smoking in childhood added an extra 3.3 years to the age of blood vessels by the time the young people reached adulthood.

"Our study shows that exposure to passive smoke in childhood causes a direct and irreversible damage to the structure of the arteries. Parents, or even those thinking about becoming parents, should quit smoking. This will not only restore their own health but also protect the health of their children into the future," commented Dr Seana Gall of the University of Tasmania.

The results stood even when other factors were taken into account such as the children's smoking habits, body mass index, and cholesterol levels in adulthood.

However, the study did find that this effect was only seen among children who had been exposed to both parents smoking.

"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. We can speculate that the smoking behaviour of someone in a house with a single adult smoking is different. For example, the parent that smokes might do so outside away from the family, therefore reducing the level of passive smoking. However, as we don't have this type of data, this is only a hypothesis," Dr Gail noted.

The scientists said that their findings again highlight the importance of banning smoking anywhere that children may be present, including cars.

"Reducing young people's exposure to tobacco smoke is a public health priority," they added.

Details of these findings are published in the European Heart Journal.