Breathing secondhand smoke during childhood can lead to long-term breathing and health problems and a shorter life expectancy, according to a new scientific statement from the American Heart Association.
Even though the harms of exposing kids to cigarette smoke are well known - asthma and lung infections among them - many children still breathe this smoke at home or in public places or while riding in cars or buses, noted Dr. Geetha Raghuver, lead author of the statement.
"Minority children and those from poor backgrounds are exposed more often," Raghuver said by email.
"Cigarette smoking is very addicting and a stress reliever; this along with easy access is likely the reason that it is still prevalent," she added.
Overall, an estimated 24 million nonsmoking children and youths are exposed to secondhand smoke in the U.S., largely because of parents who smoke.
That translates to four in 10 school-aged children and one in three adolescents, Raghuver and colleagues note in the statement published in the journal Circulation.
In 2012, researchers found a nicotine byproduct called cotinine in blood samples from nearly 41 percent of U.S. children ages 3 to 11, and in 34 percent of kids ages 12 to 19 - despite declines over recent decades in both adult smoking rates and the proportions of young children and adolescents living with smokers.
Poor and non-white kids were disproportionately affected.
Those blood tests found 68 percent of low-income children and 43 percent of minority youth were exposed to secondhand smoke. While Hispanic children were slightly more likely to be exposed than white kids, the problem was most pronounced among black children.
"It is a socio-economic and a health care associated disparity issue," said Dr. Avni Joshi, a pediatrics researcher at the Mayo Clinic in Rochester, Minnesota who wasn't involved in the statement.
"Parents do not understand or are oblivious to the gravity of second and third hand smoke exposure and possible effects," Joshi added by email. "This may be related to their level of education, access to health care and role modeling in the community."
Children are more likely to become smokers themselves if their parents smoke.
Besides impacting heart function by causing damage to arteries, exposure to secondhand smoke has been associated with other cardiovascular risk factors including obesity, high cholesterol, and insulin resistance - which is linked to diabetes.
While doctors have warned parents about the dangers of secondhand smoke for years, recent research has helped explain why this can be dangerous for kids, the statement authors note.
Chemicals in secondhand smoke can cause changes to blood flow, blood vessels, blood pressure and heart rhythm.
Children are especially vulnerable to secondhand smoke exposure in part because they cannot control tobacco use in their surroundings, and they appear to be particularly susceptible physically to the smoke's effects.
But the effects of secondhand smoke may be difficult for parents to see while children are young, said Dr. Annie Lintzenich Andrews, a pediatrics researcher at the Medical University of South Carolina who wasn't involved in the statement.
"Avoidance of secondhand smoke exposure might not be on the top of many parents' list of priorities due to so many competing daily stressors like getting kids to school, paying the bills, supplying nutritious meals," Andrews said by email.
"Also, there are often not immediate, tangible negative consequences to secondhand smoke exposure in children making it difficult for parents to appreciate the risks it poses to their children," Andrews added.