Improved cooking fuels and kitchen ventilation can reduce the risk of developing lung disease, Chinese researchers said Tuesday.

The researchers, led by Pixin Ran from the Guanzhou Medical University, China, followed 996 villagers from southern China for a span of nine years to examine the effects of cleaner fuels and better kitchen ventilation on lung function and disease.

According to the researchers, an estimated three billion people worldwide heat their homes and cook by burning biomass such as wood or animal dung, hence causing more than a million deaths per year from chronic obstructive pulmonary disease (COPD).

For the study, the researchers offered nearly 1,000 participants from 12 villages access to biogas, a combustible clean fuel made by composting biomass at room temperature in a biogas digester, and improved kitchen ventilation, and people adopted these interventions according to their preferences.

The participants provided details about their lifestyle and had their lung function measured both at the outset of the study and at its end nine years later, and some were also interviewed and examined three and six years into the study.

The researchers also tested indoor air quality in a random subset of participants' households.

Compared with those who chose not to change fuel or ventilation, participants who used biogas or improved their kitchen ventilation retained more of their lung function as they aged, the researchers found.

People who adopted both improvements performed even better in lung function tests and were also less likely to develop COPD, they said.

"While we recognize that implementing community interventions to change how individuals cook in rural settings in developing countries remains a challenging task, substituting biogas for biomass fuel for cooking and improving kitchen ventilation could lead to a reduction of the global burden of COPD, especially in non-industrialized nations," the researchers concluded.

The findings were published in the U.S. journal PLOS Medicine.