Pollution from gas stoves and heaters in the home may have subtle effects on young children's cognitive development, a new study suggests.

The study, of nearly 400 Spanish preschoolers, found that those exposed to gas appliances since infancy had lower average scores on tests of memory, language skills, attention and other areas of cognition.

Similarly, measurements of nitrogen dioxide (NO2) in the home — taken during the children's first three months of life — were related to the preschoolers' cognitive test scores.

NO2 is a pollutant produced from burning fuels that is known to irritate the airways and eyes. Its potential effects on neurological development are less clear. Measurements of the gas do serve as an objective marker of children's exposure to gas appliances and the various combustion products they might release into the air, senior researcher Dr. Jordi Sunyer told Reuters Health.

Sunyer stressed that the findings show an average difference in cognitive performance between two large groups of children — and not deficits that would be apparent as learning problems in an individual child.

"These differences are relevant at population level, comparing groups of children," he said, "but have no clinical or psychological relevance at (the) individual level."

Still, Sunyer recommended that parents limit their children's exposure to pollution from gas appliances by making sure the appliances are properly ventilated and by keeping children out of the kitchen when the stove is being used.

The study, reported in the American Journal of Epidemiology, also found that genetics may make certain children more vulnerable to any cognitive effects of gas appliances.

The apparent effects of NO2 exposure were stronger among children with a particular variant of a gene called GSTP1. GSTP1 is an enzyme that helps rid the body of potentially cell-damaging substances called reactive oxygen species.

The variant in question is associated with less activity in the GSTP1 enzyme. So it's possible, according to Sunyer's team, that children with the variant are more susceptible to brain-cell changes from early- life NO2 exposure.

More studies are still needed to confirm and extend the findings, the researchers say. They also point out that in their study population, the most common source of gas-appliance fuel was butane — which is generally more toxic than natural gas.

SOURCE: American Journal of Epidemiology, June 2009.