This map shows the distribution of the almost two million deaths a year linked to cookstoves

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Millions of clean cookstoves have been deployed in the developing world, but there is very little research measuring the effectiveness of this intervention — and how it could be improved, say researchers.

Burning biomass such as charcoal, crop residues and wood for cooking and heating causes indoor air pollution, which affects three billion people worldwide. Air pollution is a leading environmental cause of death, with an estimated two million deaths occurring every year — most of them from acute lower respiratory infections, chronic obstructive pulmonary disease and lung cancer — according to the WHO.

But, although the health risks associated with indoor air pollution are clear, the amount by which emissions need to be reduced to cut those risks and improve health is still unknown, researchers said in an article published in Science today (14 October).

To date, there has been just one study into the impact of reduced exposure to indoor air pollution, said the researchers. This considered child pneumonia in Guatemala and found that as much as 90 per cent emissions reduction is required to decrease risk. It remains unclear whether other health risks required an equally drastic reduction, the authors said.

"We need to measure the levels of exposure to smoke in the homes when these new stoves are used. It is not good enough to rely on what works in the laboratory setting," William Martin, co-author of the article and associate director for disease prevention and health promotion at the US National Institutes of Health, told SciDev.Net.

"We need to be certain that the stoves really reduce smoke to such a degree that health is improved, we need to assess a large enough population and measure the health impacts directly."

He added: "There is no shortcut to research. We need to verify that similar results occur in different settings and using different health outcomes."

The authors say that around US$150–200 million would be required for research into health risks associated with indoor air pollution.

Initiatives to roll out new improved and efficient cooking stoves provide a "great opportunity" to determine whether this intervention works, said the researchers, citing the Global Alliance for Clean Cookstoves, launched by the UN Foundation, which aims to distribute clean and efficient stoves and fuels to 100 million homes by 2020.

Indoor air pollution is also linked to low birth weight, burn injuries, eye cataracts, cardiovascular disease, asthma, and tuberculosis. And burning biomass contributes to environmental degradation and deforestation. Improved and efficient stoves could help reduce fuel use and decrease black carbon (a key component of soot) emissions.