On April 3, JAMA, one of the three largest medical journals in the world, released a paper entitled “Association of solid fuel use with risk of cardiovascular and all-cause mortality in rural China” in the form of Original Investigation.

The paper is co-first-authored by Yu Kuai(Ph.D student of HUST), Qiu Gaokun (Postdoctoral candidate of HUST) and Chen Jiahong (Ph.D student of Oxford University). Prof. Wu Tangchun of HUST School of Public Health, Prof. Li Liming of Peking University and Prof. Chen Zhengming of Oxford University are the supervisors. The research is supported by funding from National Natural Science Foundation of China.

As we all know, cooking and heating are the basic conditions for human survival and development. Therefore, they are of great importance for our social development. With the development of our society, there have emerged different kinds of fuel use for cooking and heating, such as electricity, gas, central heating (clean fuel) and coal, wood, charcoal, crop waste and animal waste (solid fuel), etc. According to the statistics by WHO, about 3 billion people around the world are using solid fuels for cooking or heating, especially in low and middle income countries. Solid fuel use for cooking or heating, not only produces 100 times more fine particles (PM2.5), carbon monoxide and nitric oxid indoor than outdoor, but also emits polluted gases to the outdoor and does harm to more people. According to statistics by Global Burden of Disease Study, solid fuel use for cooking contributes up to 37% of the global PM2.5, while solid fuel use for heating makes up to 21% of the global PM2.5. Although indoor air pollution, which is mainly caused by solid fuel use, has become a major public health and social problem that endangers our human health, there is still a lack of large samples and scientific evidence of multicenter and high-quality in the health hazard characteristics of solid fuels use and its duration, especially the most health threatening cardiovascular diseases, not to mention sustainable and economically feasible preventive measures.

Based on the cohort of "China Kadoorie Biobank study (CKB)", the paper dynamically traced the health status of the subjects with conventional death reports and hospitalization records. In this cohort study, there are only 7.1% and 12.8% of people use solid fuel for cooking or heating in 5 rural areas across China, thus, this paper analyzed about 270,000 rural residents (from Sichuan, Gansu, Henan, Zhejiang, Hunan).

The study found that :

 (1) Among the 270,000 rural resident samples, the ratio of regularly cooking and heating is 66% and 60%, and the proportion of using solid fuel for cooking and heating is 84% and 90%, respectively. The results showed that about 78% and 84% of rural residents used the same fuel for cooking and heating respectively in baseline and repeated investigation;

2) after an average of 7.2 -year follow-up, compared with residents using clean fuels (including natural gas, electricity and central heating), 135 more people died for cardiovascular disease (an average increase of 20%) and 338 more people died for all-cause mortality (an average increase of 11%) per 100,000 solid fuel users for cooking at baseline every year, while 175 more people died for cardiovascular disease (an average increase of 29%) and 392 more people died for all-cause mortality (an average increase of 14%) per 100,000 solid fuel users for heating every year. Moreover, the longer solid fuel use, the more risk of mortality increases. It is worth noting that the paper is the first one to analyze the use of solid fuel cooking and heating, and found that the increase in death risk caused by cooking and heating with solid fuel is independent, which adds a strong scientific evidence to the impact of indoor air pollution on health;

3）Compared with residents using solid fuels, 138 fewer people died for cardiovascular disease (an average decrease of 17%) and 407 fewer people died for all-cause mortality (an average decrease of 13%) per 100,000 users stopping using solid fuel for cooking every year, while 193 fewer people died for cardiovascular disease (an average decrease of 43%) and 492 fewer people died for all-cause mortality (an average decrease of 33%) per 100,000 users stopping using solid fuel for heating every year. Most important, 33 fewer people died for cardiovascular disease (an average decrease of 11%) and 87 fewer people died for all-cause mortality (an average decrease of 9%) per 100,000 users using solid fuels with ventilation facilities every year. It reveals the importance of improving ventilation for reducing the risk of death when clean fuel and solid fuel are used.

The study was the first to find a significant additive effect of smoking on the use of solid fuel, while residents who smoke and use solid fuel. Compared with non -smoking individuals using clean fuel, 270 more people died for cardiovascular disease (an average increase of 76%) and 691 more people died for all-cause mortality (an average increase of 52 %) per 100,000 smoking and solid fuel users every year. Its health hazard is more serious, which shows the key points and difficulties of its preventive measures.

The merits and the sense of the study are that, according to the evidence, it is the first paper, with the first prospective cohort through large-scale, multicenter and long-term follow-up study in the world, to prove that the more indoor air pollution solid fuel use caused, the greater the risk is for cardiovascular death and all-cause modality. Furthermore, the longer the solid fuel is used, the higher death risk it is. Lower risks were observed among solid fuel users who reported having switched to clean fuels before the study baseline or using ventilation. It not only confirms the credibility of the health hazards caused by the solid fuel use, but also puts forward the preventive measures to reduce these health hazards. Although the clean fuel use is an ideal solution, using economic and effective stove ventilation facilities will significantly reduce the risk of death of these major diseases, even if the socio-economic conditions are limited, and the families can’t switch fuel now. To ensure the reliability of the results, a repeated survey of about 4% participants was used to show that the results were repeatable and credible. The study controlled, as possible as we can, the age (5 age a group), sex, research area, education level, total family income, smoking situation, drinking, passive smoking, diet and risk factors such as physical activity, body mass index, and stove ventilation, and conducted a series of stratified analysis, such as fuel types, cardiovascular death subtype, area, and sensitivity analysis (such as correction season, occupation, self-reported health status and family history of cardiovascular disease, excluding those participants who take antihypertensive drugs or use clean fuels for less than 10 years, or died within 2 years during follow-up survey, all that guaranteed the high credibility of the results. The limitation of the research is mainly due to the lack of monitoring data of indoor air pollution exposure. In conclusion, in rural China, solid fuel use for cooking and heating was associated with higher risks of cardiovascular and all-cause mortality. These risks may be lower among those who had previously switched to clean fuels and those who used ventilation, which has significant significance and practical value for public health.

Further reading: about the CKB project

The CKB project is a prospective cohort study for establishing and maintaining the international cooperation between China and Britain. It is the only large scale natural population cohort in China, as well as one of the three global prospective cohorts of about 500,000 people with a biobank in the world. The project mainly discussed the influence of environment, individual life style, physical and biochemical indicators, heredity and other factors on the occurrence and development of complex chronic diseases. With the development of the CKB project, it has become an important source of etiological evidence of localization and high quality, which will be the basis for the formulating major chronic disease control strategies and disease guidelines. Especially in the large data age, using the super large crowd cohort of CKB project is a necessary way to apply the biomedical scientific research results to the disease prediction, prevention and accurate medical treatment. It is the core support for the preventive medicine, basic medicine and clinical medicine, and an important fundamental platform for the future medical science and technology innovation, as well as a significant part of chemical medicine.