Association between household fuel types and undernutrition status of adults and children under 5 years in 14 low and middle income countries

World Health Organization (WHO) estimates that approximately 3 billion people worldwide use polluting fuels such as coal, kerosene, wood, charcoal, crop waste, or animal dung in inefficient stoves (2018). Inefficient cooking and heating with these polluting fuels in homes with poor ventilation are a major source of household air pollution (HAP) exposure in low and middle income countries (LMICs) (Balmes 2019). According to the Global Burden of Disease Study 2019, HAP from solid fuel use was among the top ten risk factors for disease and ranked as the second environmental risk factor for global disability-adjusted life-years (DALYs) (GBD 2019 Risk Factors Collaborators 2020), leading to 1.8 million deaths and 60.9 million DALYs in 2017 (Lee et al 2020). Additionally, the burden attributed to HAP in LMICs was overwhelmingly higher than that in high-income countries (60.8 million compared with 0.09 million DALYs) (Lee et al 2020). The inefficient burning and ombustion-generated substances have well-documented adverse effects on human health: particulates, such as PM₁₀ and PM_2.5; inorganic gaseous compounds, such as sulphur dioxide (SO₂) and carbon monoxide (CO); hydrocarbons, such as polycyclic aromatic hydrocarbons (PAHs); oxygenated organic compounds, such as benzene and formaldehyde; and cilia toxic respiratory irritants, such as acrolein and cresols (Guercio et al 2021). Accumulating evidence has consistently demonstrated that polluting biomass fuel use can lead to a broad range of respiratory and cardiovascular conditions in both adult and child population (Bellows et al 2020, Dai et al 2021, Mortimer et al 2020). For example, a recent meta-analysis, including 15.5 million participants from 123 countries, reported that HAP was positively associated with asthma (relative risk (RR): 1.23, 95% confidence interval (CI): 1.11, 1.36), acute respiratory infection in both adults (RR: 1.53, 95%CI: 1.22, 1.93) and children (RR: 1.39, 95%CI: 1.29, 1.49), chronic obstructive pulmonary disease (RR: 1.70, 95%CI: 1.47, 1.97), cerebrovascular disease (RR:1.09, 95%CI: 1.04, 1.14), and ischemic heart disease (RR:1.10, 95%CI: 1.09–1.11) (Lee et al 2020).

Undernutrition includes deficiencies of essential vitamins and minerals, underweight, and childhood stunting and wasting (Popkin et al 2020). Undernutrition is now still a public health issue, especially under the context of the double burden of malnutrition in LMICs, which is the coexistence of undernutrition and overweight/obesity (Popkin et al 2020). Adult underweight and child underweight, stunting, and wasting are widespread and prevalent indicators of undernutrition (Local Burden of Disease Child Growth Failure Collaborators 2020, Victora et al 2021). This is because the prevalence of them are relatively high in LMICs, the anthropometry data are easy to obtain, and the indicators are comparable across regions (Local Burden of Disease Child Growth Failure Collaborators 2020, Victora et al 2021). Globally, 462 million adults are underweight, while 144 million and 47 million children under 5 years of age are stunted and wasted, respectively, and most of them are in LMICs (World Health Organization 2020). Undernutrition among adults, especially reproductive age women, represents a serious problem not only for their own health, but also for the health and nutrition of their offspring. For example, lower pre-pregnancy body mass index (BMI) is associated with increased risks of adverse maternal and child outcomes, such as placental abruption, low birth weight, poor intellectual development, and poor intellectual, physical and mental development (Hung and Hsieh 2016, Li et al 2018). Childhood undernutrition is linked with severe short-term (e.g. delayed motor and cognitive development), medium-term (e.g. poorer school performances), and long-term consequences (e.g. abnormal metabolic status and increased risk of noncommunicable chronic diseases in adulthood) (Grillo et al 2016, De Lucia Rolfe et al 2018, Hock et al 2018).

Current evidence supports an association between smoking and lower weight of adults (Hu et al 2018), and there is also suggestive evidence linking ambient air pollution and environmental tobacco smoke (ETS) exposure with undernutrition of children (Spears et al 2019, Islam et al 2021). The combustion of the above-mentioned polluting fuels is qualitatively similar to the burning of tobacco in terms of emissions of particulate matter and gases, and the mechanisms by which smoke from polluting fuels causes adverse health effects in human subjects are likely similar (Balmes 2019). However, there are only limited studies exploring the association between biomass fuel use and undernutrition status of adults or children, and their data are all from single country (Amegah et al 2020, Islam et al 2021, Lamichhane et al 2020, Liang et al 2020). They reported that using unclean fuel was significantly associated with an increased risk of stunting in Chinese (odds ratio (OR): 1.34, 95%CI: 1.07, 1.68), Nepalese (for year 2011, OR: 1.50, 95%CI: 1.04, 2.18; for years 2006, 2011, and 2016, OR: 1.48, 95%CI: 1.16, 1.89), and Indian (for years 2005–06, OR: 1.05, 95%CI: 1.03, 1.06; for years 2015–16, OR: 1.16, 95%CI: 1.13, 1.19) children, respectively (Balietti and Datta 2017, Dadras and Chapman 2017, Islam et al 2021, Lamichhane et al 2020, Liang et al 2020). In addition, Lamichhane et al found that HAP was significantly associated with an increased risk of underweight in Nepalese children (OR: 1.35, 95%CI: 1.02, 1.79), and Amegah et al found using unclean fuel resulted in 0.81 kg m⁻² (95%CI: 0.29, 1.33) reduction in BMI of adult Ghanaian women (Amegah et al 2020, Lamichhane et al 2020). However, most of them did not differentiate the cooking place and thus the estimated effects may be biased (Amegah et al 2020, Lamichhane et al 2020, Liang et al 2020), as existing studies suggested that indoor cooking has more harmful impacts on household members (Islam et al 2021).

Therefore, this study will investigate the association between biomass fuel use and undernutrition status of adults and children under 5 years of age from multiple LMICs. Moreover, we will further stratify the exposure of biomass fuel by cooking place. Our study should be a significant addition to the literature on the environmental determinants of undernutrition status of both adult and child population, and possibly provide solid evidence on policy interventions for improving indoor air quality and subsequently promoting population health in LMICs.

2.1. Study design and data sources

2.2. Exposures

2.3. Outcomes

2.4. Covariates

2.5. Statistical analysis

3.1. Sample characteristics

3.2. Cooking fuel and risk of adult underweight

3.3. Cooking fuel and risk of child undernutrition

This study provides a comprehensive understanding of the association between high polluting fuel exposure and undernutrition indicators for women, men, and children in LMICs. Using household survey data from 14 countries, we found high polluting fuel exposure was associated with increased risk of undernutrition for adults and children, and the adverse effect of indoor cooking with high polluting fuels tended to be more pronounced.

This study revealed that the majority of household members in LMICs were exposed to high polluting fuels, and most of them were exposed to an environment of indoor cooking. According to International Energy Agency, the total number of people worldwide lacking access to clean fuels and technologies will remain largely unchanged by 2030 if no effective policy was implemented (2017). Therefore, the impact of polluting fuel exposure on health and well-being has become a noteworthy global health concern, particularly in LMICs (Shupler et al 2019). Most previous research studied the adverse effects of polluting fuel exposure on adult health outcomes, but most of them focused on lung function (Devien et al 2018), respiratory diseases (Devien et al 2018, Li et al 2019), or mortality (Yu et al 2018, 2020). Only one study from Ghana reported that polluting fuel exposure was associated with decreased BMI of women (Amegah et al 2020), which was consistent with our findings.

Some other studies focused on the impact of polluting fuel exposure on children as they were regarded as a more susceptible population. This is because children, especially those in younger age, spend more time in the house and breathe more air per minute than adults, and their respiratory and immune systems are not fully developed (Islam et al 2021). In these studies, adverse effects of polluting fuel exposure were mainly focused on respiratory disease (Khan et al 2017, Budhathoki et al 2020), birth outcomes (Sreeramareddy et al 2011, Khan et al 2017), and mortality (Kleimola et al 2015, Khan et al 2017, Naz et al 2017, Owili et al 2017, Nisha et al 2018). Only a few studies explored the association between biomass fuel use and undernutrition status of children, and they reported inconsistent results (Balietti and Datta 2017, Dadras and Chapman 2017, Amegah et al 2020, Islam et al 2021, Lamichhane et al 2020, Liang et al 2020). Studies from China, India, and Nepal found significant associations between polluting fuel or solid fuel exposure and lower child anthropometry z scores or higher risk of undernutrition, which were in line with our findings (Balietti and Datta 2017, Dadras and Chapman 2017, Islam et al 2021, Lamichhane et al 2020, Liang et al 2020). By contrast, a study from Swaziland did not identify such associations, which may be attributed to its limited sample size (Machisa et al 2013).

The mechanisms by which polluting fuel exposure causes undernutrition of adults and children are still not well understood, but it is believed to be involved in inefficient burning and combustion-generated gases, toxic pollutants, and particulate matter (PM) pathogenic processes. For example, carbon monoxide (CO) is one of the common gases emitted from inefficient burning of fuel and it was found to be a trigger of weight reduction of obese mice (Hosick et al 2014). This procedure was via elevated metabolism from upregulation of mitochondrial biogenesis and mitochondrial uncoupling causing alterations in morphology of the epidermal fat depot and adipocyte number (Hosick et al 2014). Another possible mechanism was related with interference DNA damages by toxic pollutants such as PAHs, and increased urinary PAH metabolite concentrations were found in children and adolescents from households with indoor heating or cooking (Murawski et al 2020). Moreover, a cohort study has confirmed that exposure to elevated levels of PAHs is associated with reduced fetal and child growth (Tang et al 2006). In addition, previous studies have shown that maternal ambient PM exposure, such as PM_2.5 and PM₁₀, was associated with increased risks of preterm birth and low birth weight, and these two adverse pregnancy outcomes were subsequently risk factors for childhood undernutrition (Li et al 2020a). Therefore, offspring from mothers exposed to combustion-generated PM during pregnancy are at increased risk of growth failure. It is of note that high polluting fuel exposure was still associated with indicators of child undernutrition after adjustment for parental BMI. Parental BMI was considered as a proxy for the shared environment, dietary, genetic, and economic status (Perkins et al 2016), thus this adjusted association might reflect the independent effects of polluting fuel exposure on child growth. Several other indirect pathways are also possible. HAP might cause frequent episodes of febrile respiratory illness, which would subsequently lead to elevated metabolic requirements, anorexia and less food intake, accelerated catabolism (Sinharoy et al 2020). These body responses can result in an unbalanced nutrient status, and hence to growth retardation (Sinharoy et al 2020). Then, households would allocate incomes to health-care expenses related to infections instead of food and nutrition (Sinharoy et al 2020). Furthermore, Sola et al conducted an exploratory review, and they proposed several hypotheses that people who are short of adequate and appropriate household fuel may have to alter their cooking and eating habits by reducing the meal frequency, switching to diets that require less cooking time, and undercooking their food (Sola et al 2016). Through these practices, the quantity, quality and nutritional value of the food consumed would be affected, and finally result in inadequate nutrients intake (Sola et al 2016).

To the best of our knowledge, this is the first and largest study examining the association between high polluting fuel exposure and multiple undernutrition indicators for women, men, and children in LMICs. The uniform protocols, scientific sampling methodology, and standardized questionnaires made the results accurate and reliable. This study has several limitations. First, causal inference is difficult to draw in this study because of its cross-sectional design. Therefore, our results should be interpreted with caution. Second, undernutrition is a consequence of complicated environmental, dietary, and genetic factors, but the secondary nature of the data impeded us from including some variables of interest and detailed information of exposure. For example, variables for daily nutrient intakes and adequacy, the type of cooking building, the length of time that participants had spent in their households, and the extent of their exposure to fuel were not available. Third, anthropometry data was not routinely collected for men in most DHS surveys, thus only 11 surveys from Africa and three from Asia were included, making the generalizability of our findings limited.

In conclusion, indoor high polluting fuel exposure was associated with increased risk of adult underweight and child underweight and stunting. It is fair to expect that the transition of high polluting fuels toward clean fuels for cooking in LMICs will present beneficial gains for both adult and child population health. Effective interventions should be adopted by policymakers to accelerate the transition of polluting fuels to cleaner energy and reduce the health burden. Our study also suggests that indoor cooking tends to make larger impact on child growth. Therefore, if a complete change cannot be achieved in a short period of time, at least more awareness is needed for parents to keep their children stay away from the kitchen while cooking.

The authors are grateful to The U.S. Agency for International Development (USAID) for providing the valuable DHS data.

The data that support the findings of this study are openly available at the following URL/DOI: https://dhsprogram.com/.

The research has received funding from: Key Research and Development Plan of Shandong Province (No. 2019GSF111067), Shandong Provincial Social Science Planning Research Project (No. 18CQXJ18), Shandong Medical and Health Technology Development Plan (No. 2017WS703), Teaching Reform and Research Project of Weifang Medical College (No. 2018YB013), National Steering Committee of Medical Professional Degree Postgraduate Education Project (No. C-YX20190301-04), Medical Education Research Project of Medical education Branch of Chinese Medical Association and Medical Education Professional Committee of Chinese Association of Higher Education (No. 2018A-N02079), and Health Standard Assessment Project of Chinese Center for Disease Control and Prevention (No. 20270418).

Jing Li: Conceptualization, Formal analysis, Methodology, Resources, Writing—original draft.

Xin Xu: Data curation, Resources, Validation, Writing—original draft.

Jin Li: Data curation, Methodology, Resources, Writing—original draft.

Dan Li: Data curation, Methodology, Resources, Writing—review & editing.

Qiyong Liu: Formal analysis, Software, Validation, Writing-review & editing.

Haibin Xue: Conceptualization, Data curation, Methodology, Project administration, Resources, Supervision, Writing-review & editing.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.