Association Of Solid Fuel Use With Risk Of Cardiovascular And All-cause Mortality In Rural China

Household air pollution(HAP)from solid fuel use is a leading cause of death worldwide.In 2015,around 3 billion individuals were using solid fuels derived from plant material(biomass)or coal,mostly in low-and middle-income countries(LMICs)including China where an estimated 450 million people still rely heavily on solid fuels.Solid fuels are usually used in an open fire or simple stove with incomplete combustion,and result in a large amount of pollutants such as PM2.5,carbon monoxide(CO)and nitric oxygen(NO),which could be inhaled through the airways and be harmful to human health.When burning indoor,solid fuel could generate 50-100 times higher levels of pollutants than clean fuel(such as gas,electricity and biogas).According to Global Disease Burden(GBD)study,HAP being estimated to account for 4 million premature deaths annually,and could be responsible for enormously more deaths as solid fuel use for cooking and for heating could contributed up to 37%and 21%,respectively,to ambient fine particulate matter(aerodynamic diameter<2.5 μm;PM2.5)pollution.Previous studies have examined the associations between solid fuel use and respiratory diseases(such as acute respiratory infection,chronic obstruction pulmonary disease and lung cancer)extensively,however,evidence is scarce about the prospective association between HAP and all-cause mortality risk,especially that from cardiovascular disease(CVD).CVD is the leading cause of mortality across the world in the last 15 years.Previous studies have examined the associations of CVD risk factors such as ambient air pollution and smoking with CVD extensively.However,despite the high similarity between solid fuel smoke and cigarette smoke,few studies have investigated the association between HAP and CVD.The evidence of CVD effects at higher exposures(active smoking)and lower exposures(ambient air pollution and second-hand smoking)argues that HAP exposure levels likely produce adverse effects.Since no epidemiologic studies were available for HAP at the time of preparing the GBD study,the Integrated exposure-response method was used to interpolate risk estimates and 95%CIs for CVD.Direct evidence of the magnitude of mortality risk over the general global exposure level is still lacking.Consequently,much uncertainty remains concerning the association of solid fuel use with all-cause mortality risk,especially the mortality risk from cardiovascular causes.In addition,few studies have examined solid fuel use for cooking and heating separately,which are different in exposure patterns.Furthermore,it remains unclear whether mortality risk associated with solid fuel use,if any,is lower among adults who had switched from solid to clean fuel use or used appropriate ventilation(e.g.ventilated cookstoves).Despite large reductions in the prevalence of solid fuel use during the past decades,over a half of Chinese residents still use solid fuels for daily cooking or heating.It is noteworthy that,most urban residents have changed to use clean fuels such as gas or electricity,while for most rural residents,solid fuels are still their primary fuel types.According to World Health Organisation(WHO),if no substantial changes in policy,the total number of residents using solid fuels will remain largely unchanged by 2030.The China Kadoorie Biobank(CKB)study was designed to investigate the effects of different genes,environmental factors and lifestyles on prevalent chronic diseases which are unique to the Chinese population.The CKB study recruited participants from 10 diverse geographic areas,including 5 rural areas(Sichuan,Gansu,Henan,Zhejiang and Hunan)and 5 urban areas(Shandong,Harbin,Hainan,Jiangsu and Guangxi).During 2004 to 2008,512891 adults aged 30-79 were recruited.Detailed questionnaire data were collected from each participant,including demographic and socio-economic factors,cigarette smoking,alcohol drinking,diet factors,height,weight,physical activity,pre-existing diseases and related medication,and HAP related information.Based on this nationwide prospective cohort study,we first examined the association of solid fuel use with risk of cardiovascular and all-cause mortality in rural China.Second,we explored the effects of previously change from solid fuels to clean fuels,or cookstoves ventilation on mortality risk.Finally,we performed stratified analyses for established risk factors,and explored the joint effect of cigarette smoking and solid fuel use.Objectives:To assess the associations of solid fuel use for cooking and for heating with cardiovascular and all-cause mortality.Methods:This nationwide prospective cohort study recruited participants from 5 rural areas(Sichuan,Gansu,Henan,Zhejiang and Hunan)across China between June 2004 and July 2008,and mortality follow-up was until.January 1,2014.A total of 271217 adults aged 35-79 without a self-reported history of physician-diagnosed cardiovascular disease at baseline were included,with a random subset(n=10892)participating in a resurvey after a mean interval of 2.7 years.Self-reported primary cooking and heating fuels(solid:coal/wood/charcoal;clean;gas/electricity,or central heating),switching of fuel type before baseline and use of ventilated cookstoves were the main exposures evaluated in this study.Death from cardiovascular and all causes,collected through established death registries.Cox regression yielded adjusted hazard ratios(HRs)for cardiovascular and all-cause mortality associated with solid fuel use.Results:Among the 271217 participants,the mean(standard deviation[SD])age was 51.0(10.2)years,and 59%(n=158914)were women.66%(n=179952)of the participants reported regular cooking(at least weekly)and 60%(n=163882)reported winter heating,of whom 84%(n=150992)and 90%(n=147272)used solid fuels,respectively.There were 15468 deaths,including 5519 from cardiovascular causes,documented during 7.2(1.4)years of follow-up.Use of solid fuels for cooking was associated with greater risk of cardiovascular mortality(absolute rate difference[ARD]per 100000 person-years,135[95%CI:77-193];hazard ratio[HR],1.20[95%Cl:1.02-1.41])and all-cause mortality(ARD,338[95%CI:249-427];HR,1.11[95%CI:1.03-1.20]).Use of solid fuels for heating was also associated with greater risk of cardiovascular(ARD,175[95%CI:118-231];HR,1.29[95%CI:1.06-1.55])and all-cause mortality(ARD,392[95%CI:297-487];HR,1.14[95%CI:1.03-1.26]).Compared with persistent solid fuel users,participants who reported having previously switched from solid to clean fuels for cooking had lower risk of cardiovascular(ARD,138[95%CI:71-205];HR,0.83[95%CI:0.69-0.99])and all-cause mortality(ARD,407[95%CI:317-497];HR,0.87[95%CI:0.79-0.95]),while for heating the ARDs were 193(95%CI:128-258)and 492(95%CI:383-601),and HRs were 0.57(95%CI:0.42-0.77)and 0.67(95%CI:0.57-0.79),respectively.Among solid fuel users,use of ventilated cookstoves was also associated with lower risk of cardiovascular(ARD,33[95%CI:-9-75];HR,0.89[95%CI:0.80-0.99])and all-cause mortality(ARD,87[95%CI:20-153];HR,0.91[95%CI:0.85-0.96]).Conclusions: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.In summary,taking advantage of this large-scale multi-center prospective cohort study,we first observed elevated risks of cardiovascular and all-cause mortality associated with current solid fuel use.These risks may be lower among those who had previously switched to clean fuels and those who used ventilation.Our study provided strong evidence regarding solid fuel use and mortality risk.There is an opportunity and perhaps a responsibility for policy makers and scientists to make policies and approaches that could reduce adverse health effects from HAP.