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Up to three billion people worldwide rely on solid fuels such as wood, coal, crop waste or animal dung for indoor cooking and heating. The resulting household smoke ranks as a major health risk for pneumonia and cognitive impairment, new research suggests. (Rajesh Nirgude/Associated Press)

Smoke from open fires and dirty cookstoves — used by almost half the world's population — is linked to severe pneumonia, especially among women and young children, a new study has found.

Researchers from the University of California at Berkeley carried out a randomized controlled trial in Guatemala that compared households with traditional open woodfires to those that had a woodstove with a chimney that vented smoke to the outside.

The researchers found that the number of cases of severe pneumonia was a third lower among children in homes with smoke-reducing chimneys attached to their cookstoves.

"The amount of smoke exposure babies were getting from the open woodfire stoves is comparable to having them smoke three to five cigarettes a day," said Kirk Smith, a professor at UC Berleley's School of Public Health and principal investigator of the RESPIRE study (Randomized Exposure Study of Pollution Indoors and Respiratory Effects).

"The chimney stoves reduced that smoke exposure by half, on average," he said.

About three billion people worldwide use open fires and dirty cookstoves as the primary source of cooking and heating.

Researchers say their findings are important because they provide evidence that reducing household smoke exposure is a public health measure that's worth investing in, saying it's "on a par with vaccinations and nutrition supplements for reducing severe pneumonia."

Pneumonia kills 1.4 million children a year in the developing world and is the leading cause of death for children under the age of five.

The RESPIRE study is published in Thursday's edition of the journal Lancet.

Woodsmoke linked to cognitive impacts

A second study, published in the journal NeuroToxicology, uncovered a surprising link between prenatal maternal exposure to woodsmoke and poorer performance in markers for IQ among their children years later.

Researchers found impairments in visual-spatial perception and integration, visual-motor memory, and fine motor skills.

"I was surprised because woodsmoke was always considered a risk for respiratory health, but not IQ," said the study's lead author, Linda Dix-Cooper, a graduate student at UC Berkeley's Global Health and Environment graduate program.

Researchers measured carbon monoxide levels in 39 mother and child pairs. Exposure to woodsmoke during the third trimester of pregnancy was linked, for the first time, to lower performance on neurodevelopmental tests when their children were six to seven years of age.

"The implications of our findings are highly worrisome," said Dix-Cooper. "Neurodevelopmental impacts have societal costs, such as impacts on an individual's future lifetime earnings and educational attainment."

Both of the woodsmoke studies draw further attention to the urgent need for cleaner burning cookstoves in the developing world.

The United Nations Foundation launched the Global Alliance for Clean Cookstoves last year.