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Exposure to household air pollution from using wood or coal for cooking and heating is associated with higher risk of death from heart attack and stroke, according to new research published in JAMA today.

Around 3 billion people worldwide use solid fuels such as coal, wood, charcoal and crop wastes to cook and to heat their homes. When burnt, these fuels produce smoke that contains a very high concentration of fine particles (known as PM2.5) and other harmful substances, especially in houses without adequate ventilation. It was estimated that worldwide about 2.5 million deaths in 2016 were related to the resulting household air pollution. In China, despite the rapid urbanisation in recent decades, about one in three people still rely heavily on solid fuels, mostly coal and wood, for domestic purposes. The health impact of household air pollution on the Chinese population is therefore believed to be substantial, but previous research has not provided concrete evidence.

Researchers from the University of Oxford, and Huazhong University of Science and Technology, the Chinese Academy of Medical Sciences, and Peking University in China have studied the association of the long-term use of solid fuels for cooking and heating with the risk of death from cardiovascular disease in a large study of 271,000 people in five rural areas in China where use of solid fuels for domestic purposes is still common. This study is based on the China Kadoorie Biobank prospective study of 0.5 million adults which was established jointly by the University of Oxford and Chinese Academy of Medical Sciences during 2004-08. The health of study participants was monitored through linkages to death registries for an average of seven years. Among those with no history of cardiovascular disease at recruitment over 5,500 participants died of cardiovascular disease (e.g. stroke, heart attack) during this time.

The researchers found that, compared with people who mainly used gas or electricity (‘clean fuels’), those who regularly cooked using coal or wood (‘solid fuels’) had a 20% higher mortality risk from cardiovascular disease, and people who heated their homes using solid fuels had a 29% increase in risk, after taking account of the effects of age, sex, socio-economic status, smoking, alcohol drinking, diet, physical activity, and adiposity. The study also showed clearly that the longer people used solid fuels, the higher the risk of death. Moreover, there were synergistic effects of household air pollution and tobacco smoking, with the risk of death from cardiovascular disease being 76% higher among smokers who used solid fuel than non-smokers who used clean fuels.

Study author, Professor Zhengming Chen, the co-lead Principal Investigator of the China Kadoorie Biobank, said “Air pollution has caused a lot of concern in China, but people have been focusing mainly on the outdoor air quality and overlooking the health consequences of pollution arising from domestic burning of coal and wood for cooking and heating, which may have a more profound impact on health”.

The study showed that switching from solid to clean fuels for cooking reduced the risk of cardiovascular death by 17% and switching from solid to clean fuels for heating reduced the risk by 43%. An equally important finding was that individuals who cooked on stoves using solid fuels but had proper ventilation had an 11% lower risk, compared with those whose stoves were not properly ventilated.

In recent decades, the Chinese government has launched a massive campaign to replace traditional cooking stoves and to encourage more widespread use of clean fuels. Findings from this study confirm the health benefits of switching to clean fuels and having proper ventilation. Despite this, use of solid fuel to cook and heat and poor ventilation are still prevalent in many rural areas of China, which will continue to cause many premature deaths from vascular and many other diseases.