Shuyi Qiu and John S Ji
Many people around the world are still using biomass as a fuel for cooking and heating. Inefficient combustion of solid fuels is the primary cause of indoor household air pollution, estimated to be responsible for 4.3 million premature deaths in 2012 (7.7% of total mortality).
The World Health Organization’s latest global air quality guidelines point out that indoor air pollution causes a health burden that mostly affects people in low- and middle-income countries. Many global development agencies are working with governments of developing countries to reduce household air pollution. For example, China’s Relocation Program in the poorest provinces is a significant part of China’s poverty eradication plans. This large-scale program relocates millions of residents in absolute poverty to places with better living conditions, including fuel type.
The 2019 Nobel Prize in Economics was awarded to Abhijit Banerjee, Esther Duflo and Michael Kremer for studying what makes it difficult for people to escape poverty. A poverty trap is formed in a society when a certain level of disposable capital is required to escape poverty. The inability of a household or individual to acquire sufficient capital creates a self-reinforcing cycle of poverty.
In our research recently published in the IJE, we advance this theory by correlating solid fuel use with socioeconomic status and diseases. We found that solid fuels used for cooking or heating are a potential mediator between socioeconomic factors and health status. A poverty trap is therefore not simply an absence of economic means; there are other factors at play, such as access to clean fuel and the high cost of health care. These factors work together to keep an individual or family trapped in poverty.
We used a subset of the baseline data (2004–2008) and follow-up endpoint data (to 31 December 2013) from the China Kadoorie Biobank. The data were a sample from Pengzhou, in Sichuan Province, a low-income rural area. While cities along the east coast of China have benefited from the reform and opening policy, inland areas like Pengzhou have lagged behind.
As the cut-off point for determining level of socioeconomic status, we used an annual household income of ¥5878 (or £286) and 6.01 years of education (or primary school) from the data of 12 western provinces (including Sichuan) in the statistical yearbook data. Disease outcomes, based on health insurance data during the follow-up period, were automatically recorded. We found that participants with less education or low income had a higher probability of using solid fuel. They also had a higher risk of cardiovascular disease and all-cause mortality, probably due to less awareness of the possible harms of solid fuels and to the limits of the household budget.
Based on this direct causal path, we applied the method of mediation analysis to estimate the percentage of solid fuel use that contributed to the effect of socioeconomic status on cardiovascular disease and all-cause mortality. We showed that, among those who cooked daily, 42.4% of the effect of poor education and 55.2% of the effect of low income on all-cause mortality could be explained by the use of solid fuel for cooking. The use of solid fuel for heating accounted for more than 75% of the effect of poor socioeconomic status on cardiovascular disease and all-cause mortality.
Furthermore, we found an association between longer duration of solid fuel use and a higher risk of cardiovascular disease and all-cause mortality. Those who had used solid fuels had a 30% to 40% higher risk than those who had not. Switching to clean fuel, such as gas or electricity, could reduce this risk by 10% in cooking and 24% in heating.
While China transformed itself from a low-income to a middle-income country by introducing a market economy system and by targeting poverty alleviation during the Millennium Development Goals era, our research on this topic should give policymakers clues about the need to continue poverty alleviation. Continued progress to achieve the Sustainable Development Goals should simultaneously consider poverty, solid fuel use and health outcomes. Targeting the source of household energy might be low-hanging fruit to produce a high public health impact and break the poverty cycle.
Qiu S, Chen X, Chen X, et al. Solid fuel use, socioeconomic indicators and risk of cardiovascular diseases and all-cause mortality: a prospective cohort study in a rural area of Sichuan, China. Int J Epidemiol 2021; 18 September. doi: 10.1093/ije/dyab191.
Shuyi Qiu is a Master in Public Policy candidate in the Sanford School of Public Policy at Duke University. Her research interests centre on social determinants of health outcomes and the poverty trap.
John S Ji is an associate professor in the Vanke School of Public Health at Tsinghua University. His main interests are in environmental epidemiology and ageing.