A vast study on over 20,000 people in China demonstrates the significant role of so-called indoor air pollution, particularly smoke from coal or wood fires in kitchens. Its results are published today in the online edition of the ERJ, the scientific publication of the European Respiratory Society (ERS).

COPD (Chronic Obstructive Pulmonary Disease), which includes chronic bronchitis and emphysema, represents a major global public health problem. While this severe respiratory condition is known to be caused mainly by smoking, which is very widespread in China, it is far from rare among non-smokers. Indeed, as shown by this study in the European Respiratory Journal (ERJ), over a third of Chinese COPD patients (38.6%) have never touched a cigarette!

The prevalence of COPD among non-smokers varies widely from one country to another: from only about 6% in Mexico City, it rises to 9% in the USA and nearly 16% in Santiago de Chile. This range points clearly to important differences in lifestyle, behaviour and exposure to various toxic substances.

It was precisely in order to identify COPD risk factors among non-smokers in China that Pixin Ran (University Hospital of Guangzhou, Guangdong, China) decided to undertake, with his team, a vast study on the basis of a known cohort of Chinese COPD sufferers. The cohort (known as CESCOPD), established between 2002 and 2004, was recruited in seven Chinese provinces with a total population of over 230 million people in rural and urban areas.

From 20,245 subjects aged over 40, interviewed and examined by spirometry, the team analysed the data of 12,471 non-smokers and 1,024 smokers with COPD. The selected volunteers completed a detailed questionnaire on their smoking habits, personal and familial antecedents of respiratory disease, and the presence of respiratory symptoms, especially chronic cough. They were also questioned about their lifestyle, especially exposure to smoke from solid fuels (mainly wood and coal, but also grass and dung) used for heating and cooking. The COPD diagnosis was duly established using spirometry with bronchodilation tests.

Kitchen smoke a major suspect

The groundbreaking results published in the ERJ will shed new light on the characteristics of COPD in China. Pixin Ran shows, firstly, that a third of COPD cases (38.6%) are unconnected with tobacco, and 5.2% of affected non-smokers have COPD. Importantly, though, the respiratory disease was found to have a very different profile among the non-smokers. By adjusting all of the variables, Pixin Ran and his team are able to conclude that exposure to various types of smoke in the home (coal, biomass etcŠ), is a leading cause of COPD in non-smokers. Passive smoking naturally plays a part, but on a comparable level to inadequate ventilation of the kitchen.

The Chinese study shows that almost half of the non-smokers (44.6%) had been exposed, for at least one year, to smoke from the burning of biomass for cooking, and 73.2% had been exposed to smoke from coal used for heating or cooking. Poor kitchen ventilation was an aggravating factor in four out of ten cases. This is a matter of no small importance: the researchers found that not only women are harmed by cooking smoke. Men, who had been exposed to it, also pay a heavy price. Furthermore, the authors of the ERJ article report that nearly four-fifths of the Chinese non-smokers (78.2%) had lived with tobacco fumes. While it is already common knowledge that children of smoking parents are more likely to suffer from respiratory disease when they reach adulthood, the problem seems particularly acute in China, where nearly 40% of adults smoke, a much higher proportion than in many European countries.

Prevention is possible

This original Chinese study also reveals other important factors. Pixin Ran and his colleagues emphasise, for example, that COPD is commoner among older men and those with lower educational attainment, or with family or personal antecedents of respiratory disease. A low body mass index (BMI) is also statistically associated with COPD. However, occupational exposure to fumes or dust was not identified as an independent risk factor among non-smokers. The relative significance of the different parameters also varied slightly according to the stage of development of the respiratory condition.