Children whose parents smoke around them are more likely to go on to develop heart disease as adults, a new study suggests.

Researchers tracked the health of Finnish people who had taken part in a study as children. Their exposure to parental smoking was assessed in the early 1980s and their heart health was then checked in 2001 and 2007.

In 2014, researchers measured the participants' childhood blood cotinine levels from samples that had been collected and frozen in 1980. Cotinine is a by-product of nicotine that is found in the blood and saliva. It is often used as a measurement of smoke exposure.

Almost 85% of children who lived with non-smoking parents had non-detectible cotinine levels. This figure fell to 62% for children living with one parent who smoked, and 43% for children who lived with two smoking parents.

The study found that overall, those who were exposed to parental smoking were almost two times more likely to have carotid plaques. Plaques are fatty deposits that clog the blood vessels. The carotid arteries are major blood vessels in the neck that supply blood to the brain. If they become blocked, carotid artery disease results.

The researchers noted that if a parent attempted to limit their child's exposure to their smoking, the risk was slightly lower, however if the parents did not limit exposure, their child's risk of having carotid plaques later on was four times higher.

"Although we cannot confirm that children with a detectable blood cotinine in our study was a result of passive smoke exposure directly from their parents, we know that a child's primary source of passive smoke exposure occurs at home," commented Dr Costan Magnussen,of the University of Tasmania in Australia and the University of Turku in Finland.

The researchers said that these findings add to the increasing evidence that passive smoking in childhood can affect a person's heart health for many years to come.

"For parents who are trying to quit smoking, they may be able to reduce some of the potential long-term risk for their children by actively reducing their children's exposure to secondhand smoke (i.e. not smoking inside the home, car, or smoke well away from their children). However, not smoking at all is by far the safest option," Dr Magnussen said.

Details of these findings are published in the journal, Circulation.

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