Secondhand smoke appears to raise blood pressure in boys, but not girls, according to a new study. The findings suggest that the effects of tobacco smoke on the cardiovascular system begin at an early age.

UPI reports that the study, conducted by researchers at the University of Minnesota, looked at 6,421 youths’ exposure to secondhand smoke. They found that among boys, secondhand smoke exposure significantly raised systolic blood pressure (the top number in a blood pressure reading). The researchers note that elevated blood pressure in childhood is an established predictor of adult high blood pressure.

The study found that in girls, however, secondhand smoke exposure was associated with lower systolic blood pressure, compared with girls not exposed to smoke. Lead researcher, Jill Baumgartner, said that the findings support previous research suggesting that something about female gender may protect against harmful blood vessel changes from exposure to secondhand smoke. The article notes that it is not known whether changes in blood pressure are reversible if children are removed from smoky environments.

The researchers presented their findings at the Pediatric Academic Societies annual meeting in Denver.