New research suggests that teens exposed to their parents' smoking may have a higher risk of developing heart disease in adulthood than those whose parents didn't smoke.

Researchers found that children whose parents smoke had almost two times the risk of developing carotid plaque in adulthood than children of parents who did not smoke. Further, risk was elevated whether parents seemed to limit their children's exposure.

The findings add to the growing evidence that exposure to smoking from parents has a lasting effect on children's cardiovascular health in adulthood.

For the study, researchers tracked participants in the Cardiovascular Risk in Young Finns Study, which included childhood exposure to parental smoking in 1980 and 1983. They collected carotid ultrasound data in adulthood in 2001 and 2007.

In 2014, researchers measured participant's childhood blood cotinine levels from samples collected and frozen in 1980. Cotinine is a biomarker of passive smoke exposure.

The percent of children with non-detectable cotinine levels were highest among households where neither parent smoked (84 percent), decreased in households where one parent smoked (62 percent) and were lowest among households where both parents smoked (43 percent).

The risk of developing heart disease was almost two times (1.6) higher in children whose parents smoked, but seemed to limit their children's exposure. It was four times higher in children whose parents smoked but did not seem to limit their children's exposure.

"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," Costan Magnussen, lead author of the study and senior research fellow at the Menzies Institute for Medical Research, University of Tasmania in Australia, said in a statement.

Researchers stressed that to provide the best long-term cardiovascular health for their offspring, parents should not smoke.

However, "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)," said Magnussen. "Not smoking at all is by far the safest option."

The findings are detailed in the journal Circulation.