Updated

Children living with people who smoke indoors miss more school than their classmates living in smoke-free households, a study out Monday shows.

Researchers at Massachusetts General Hospital (MGH) in Boston compiled data from the 2005 National Health Interview Study, a yearly in-person survey of representative US households, for their study published in Pediatrics.

The data showed that schoolchildren, aged six to 11, living with one person who smoked tobacco indoors had an average of 1.06 more days absent than kids living in homes where no one smoked inside. Those living with two or more in-home smokers missed an average of 1.54 more school days.

Depending on how many smokers were in the household, one quarter to one third of those absences were due to illnesses that have been linked to exposure to secondhand smoke, including ear infections and chest colds.

The study also looked at the potential economic implications for the higher rate of absences.

"The total impact nationwide was $227 million in lost wages and household work for the families of the 2.6 million children living with smokers and for their employers," said the paper's lead author Douglas Levy, of the Mongan Institute for Health Policy at MGH.

"Since almost half of the smoking households in our study had low incomes, that impact may be strongest on households least able to afford it," he added.

One third of children nationwide live with at least one smoker and more than half of those kids, aged three to 11, have been found with detectable levels of a blood marker for tobacco exposure, the study's authors noted.