Lead researcher Dr. Seana Gall, a research fellow in cardiovascular epidemiology at the Menzies Research Institute Tasmania, and colleagues in Finland, said the thickening of the arteries' walls associated with being exposed to parents' smoking, means the exposed children will be at greater risk of heart attacks and strokes later in life.
The study involved 2,401 participants in the Cardiovascular Risk in Young Finns Study, which began in 1980, and 1,375 participants in the Childhood Determinants of Adult Health study, which began in 1985 by the University of Tasmania's Menzies Research Institute.
The children were ages 3 to 18 at the start of the studies. The researchers asked questions about parents smoking habits and they used ultrasound to measure the thickness of the children's artery walls once they had reached adulthood.
The study, published in the European Heart Journal, found artery walls were thicker in children exposed to both parents smoking versus children whose parents did not smoke.
"Our study showed that exposure to passive smoke in childhood causes a direct and irreversible damage to the structure of the arteries," Gall said in a statement.
The researchers took account of other factors that could explain the association such as education, the children's smoking habits, physical activity, body mass index, alcohol consumption and biological cardiovascular risk factors such as blood pressure and cholesterol levels in adulthood.
However, 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," Gall said.
"We can speculate that the smoking behavior 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."