Keywords
Biomass fuel, cardiovascular diseases, household air pollution, kitchen smoke, cooking fume
This article is included in the Energy gateway.
Biomass fuel, cardiovascular diseases, household air pollution, kitchen smoke, cooking fume
Cooking smoke is a major source of household air pollution, which affects billions of people around the world, especially in developing countries. Globally, nearly 3 billion people still use solid fuels (wood, charcoal, crop residues, and dung) for cooking and heating1. Smoke from wood burning contains a large number of pollutants, including particulate matter, carbon monoxide, nitrogen dioxide, formaldehyde, and a number of highly toxic organic compounds, such as benzene, 1, 3 butadiene, benzo[a]pyrene and other toxic polycyclic aromatic hydrocarbons2.
The use of solid fuel for cooking and/or household energy sources increases respiratory and non-respiratory illnesses in both adults and children. Those effects that are well established are acute respiratory infections, chronic obstructive pulmonary disease (COPD), lung cancer, asthma, tuberculosis, and cataracts3,4. In children, biomass use is related to mortality, and acute lower respiratory tract infections, and some other non-respiratory illness, such as poor lung function, low birthweight, nutritional deficiency, and impairment of learning ability5,6.
Though with limited evidence, recent studies linked biomass smoke exposure and cardiovascular diseases (CVD), e.g. coronary heart disease (CHD), hypertension or high blood pressure (HBP), diabetes, and stroke7–10. In laboratory studies, chronic exposure to biomass smoke increased the thickness and plaque of blood vessels11. In epidemiological studies, Peruvians who live in high altitude environments and use biomass fuel had an elevated prevalence of HBP12. A study among villager women in Bangladesh reported an association between elevated cumulative exposure to biomass smoke and the prevalence of HBP13. A similar result was found in a study in Shanghai Putuo, which found using solid fuel increases the risk of HBP, CHD, and diabetes14; and a study in Shanxi, China reported an increased risk of HBP, CHD, stroke, diabetes, and dyslipidemia15 A recent study by Yu et al.16 also linked solid fuel use to cardiovascular mortality.
On a global scale, CVD is the number one cause of death and is responsible for about 18 million deaths annually17. In Thailand, CVD accounts for 23% of the national mortality18. Currently, there is no study on the effect of biomass smoke on CVD in Thailand. It was reported that about 40% of Thai households still use biomass, mainly charcoal, wood, and agriculture residue, for cooking19. The objective of this study is to investigate a possible association between biomass use for cooking and cardiovascular diseases, including CHD, HBP, HC, diabetes, and stroke. The study uses data from a cross-sectional survey among rural villagers in Phitsanulok, Thailand. The result could be used for disease prevention and control, and to support the global literature.
This is cross-sectional study. Participants are rural villagers living in Phitsanulok Province, Thailand. Phitsanulok is a midsize province located about 400 km north of Bangkok. There are 866,891 people in the area of 9 districts. Most of the people are rice farmers20.
Participants were randomly selected using multistage sampling. Out of the 9 districts in Phitsanulok province, 5 were randomly selected. In each district, one sub-district and a local health-promoting hospital were approached. In each sub-district with support from the local health-promoting hospital, a total of 1,150 households were approached and 1,134 (98.6%) people agreed to participate in the study. In each household, only one participant who was responsible for household cooking and aged over 20 years was selected. After data cleanup, 56 (4.9%) items of data were missing important information, such as age, gender, cooking practice. The final data from 1,078 people were used for statistical analysis.
The minimum sample size was calculated to be 1,034, using unmatched cross-sectional study with the following assumptions: two-sided significance level = 95%; power of detection = 80%; percent unexposed with outcome = 5%; and odds ratio = 2.0.
Data was collected using a face-to-face interview questionnaire, which was administered by 15 village health volunteers (provided as Extended data in English21). The interviews took place in the house of participants. The data was collected during the period of May–June 2017. Health volunteers were all trained on how to properly carry out the interview and use the questionnaire. The questionnaire was designed to collect information on demographic data, fuel use for cooking, and other cooking practices. In addition to general demographic data, participants were also asked a history of tobacco use (ever, never), and working in factory environments using “yes” or “no” questions. Ever smoker referred to those who smoke more than 100 cigarettes in their lifetime. Data on pesticide use was also measured by “yes” or “no” questions: “Have you ever spray or mix pesticide?”. For cooking fuel data, we asked about the types of fuel they used for cooking food (wood, charcoal, LPG, electricity), and the frequency of using each types of fuel. Data collected on cooking practices were types of cooking oil, the frequency of tears while cooking (TWC) (never, sometimes, often), kitchen location (inside a house, outside a house, both inside and outside a house), and the characteristics of kitchen ventilation (good or poor ventilation).
The presence of cardiovascular disease was determined by the participant response to the question: “Have you ever been diagnosed with the following diseases (coronary heart disease (CHD), high blood pressure (HBP), high cholesterol (HC), diabetes mellitus, stroke) by a medical doctor?”. For diseases among their family members, we asked “Did you have a family member with the following diseases?”.
The content validity of the questions was tested by three experts, and the Index of Item Objective Congruence (IOC) was between 0.7–1.0. The questionnaire was also tested for question sequencing and understanding using a group of 30 people with a similar background to the intended participants.
Demographic and prevalence of cardiovascular disease were descriptively analyzed. Comparison between groups were analyzed using chi-square test for categorical variables, and independent t-test for continuous variables. The association between cardiovascular disease was analyzed using logistic regression with odds ratios (OR) and 95 percent confidence interval (CI) adjusted for gender (male, female), age (continuous data), cigarette smoking (ever, never), living smoker (yes, no), working with smokers (yes, no), and exposure to air pollution (yes, no). All statistical analyses were performed using IBM SPSS version 19 and OpenEpi (online version 3.01). Statistical significance was set at a p-value of less than 0.05.
Most of the respondents were women (84.2%) with a mean age of 53.04 ± 12.93 yr. The highest education levels were primary school or high school. Most were farmers (36.0%) and 20.2% were causal workers on farms. About 10% were smokers and 33% lived with a smoker. Additional information on the demographic data is shown in Table 1 and in Underlying data22.
About 70% of the respondents reported using biomass for cooking (Table 2). However, when asked for fuel types that they usually use for cooking, 64.5% reported LPG and 32.3% charcoal. Among those who use charcoal, 38.6% use it often. About half have a kitchen located inside a house with good ventilation. Almost all reported having TWC either sometimes or often. Most of them cook every day.
Characteristics | Biomass, n (%) | LPG, n (%) | P–value* |
---|---|---|---|
Gender | |||
Male | 114 (15.1) | 56 (17.4) | 0.341 |
Female | 642 (84.9) | 266 (82.6) | |
Age | |||
20–30 | 34 (4.5) | 33 (10.2) | <0.001** |
31–40 | 89 (11.8) | 47 (14.6) | |
41–50 | 132 (17.5) | 73 (22.7) | |
51–60 | 249 (32.9) | 94 (29.2) | |
61–70 | 204 (27.0) | 54 (16.8) | |
71–80 | 48 (6.3) | 21 (6.5) | |
Education completed | <0.001** | ||
Primary school | 569 (76.9) | 188 (60.1) | |
Secondary school | 142 (19.2) | 104 (33.2) | |
College diploma or higher | 29 (3.9) | 21 (6.7) | |
Missing | 16 (2.1) | 9 (2.8) | |
Occupation | <0.001** | ||
Farmer | 299 (39.6) | 89 (27.6) | |
Grocer | 54 (7.1) | 35 (10.9) | |
Private or government employee | 36 (4.8) | 21 (6.5) | |
Causal worker | 130 (17.2) | 88 (27.3) | |
Housewife | 161 (21.3) | 62 (19.3) | |
other | 76 (10.1) | 27 (8.4) | |
Cigarette smoking | 0.490 | ||
Ever smoke | 81 (10.7) | 30 (9.3) | |
Never smoke | 675 (89.3) | 292 (90.7) | |
Living with smokers | 0.475 | ||
Yes | 259 (34.4) | 103 (32.2) | |
No | 493 (65.6) | 217 (67.8) | |
Missing | 4 (0.5) | 2 (0.6) | |
Working with smokers | 0.054 | ||
Yes | 131 (17.5) | 41 (12.8) | |
No | 616 (82.5) | 279 (87.2) | |
Missing | 9 (1.2) | 2 (0.6) | |
Working in a factory | 0.077 | ||
Yes | 113 (15.1) | 62 (19.4) | |
No | 637 (84.9) | 257 (80.6) | |
Missing | 6 (0.8) | 3 (0.9) | |
Using pesticides | 0.001** | ||
Yes | 321 (42.6) | 104 (32.3) | |
No | 433 (57.4) | 218 (67.7) | |
Missing | 2 (0.3) | ||
Kitchen location | <0.001** | ||
Inside a house | 364 (48.6) | 206 (64.8) | |
Both inside and outside | 109 (14.6) | 25 (7.9) | |
Outside a house | 276 (36.8) | 87 (27.4) | |
Kitchen ventilation | 0.580 | ||
Good | 504 (96.9) | 247 (97.6) | |
Poor | 16 (3.1) | 6 (2.4) | |
Cooking frequency | 0.035** | ||
Everyday | 699 (92.5) | 285 (88.5) | |
Someday | 57 (7.5) | 37 (11.5) |
The study found HBP, HC, and diabetes to be the most common cardiovascular outcomes (Table 3). Compared to non-user group, biomass users had a significantly higher prevalence of HBP, and HC, and their family members also had more incidence of HBP, HC, diabetes, and heart disease.
Disease | Biomass, n/total n (%) | LPG, n/total n (%) | p–value* |
---|---|---|---|
High blood pressure, HBP(R)a | 214/750 (28.5) | 66/321 (20.6) | 0.007** |
High blood pressure, HBP(F)b | 152/729 (21.0) | 44/305 (14.4) | 0.014** |
High cholesterol, HC(R) | 166/748 (22.2) | 48/320 (15.0) | 0.007** |
High cholesterol, HC(F) | 120/729 (16.5) | 21/305 (6.9) | <0.001** |
Diabetes(R) | 91/751 (12.1) | 30/321 (9.3) | 0.189 |
Diabetes (F) | 62/729 (8.5) | 14/305 (4.6) | 0.028** |
Coronary heart disease, CHD(R) | 20/749 (2.7) | 6/321 (1.9) | 0.521 |
Coronary heart disease, CHD(F) | 20/728 (2.7) | 2/304 (0.7) | 0.034** |
Stroke(R) | 10/750 (1.3) | 3/321 (0.9) | 0.585 |
Stroke (F) | 16/729 (2.2) | 3/305 (1.0) | 0.186 |
Further analysis using logistic regression and control variables, revealed that compared to gas users, biomass users had family members with elevated CHD, HBP, HC, and diabetes (Table 4). Among different types of fuel, household cooks using wood had a significant elevated risk of CHD (OR=7.64, 95%CI 1.18-49.61), and their family members had an elevated risk of HC (OR=1.52, 95%CI 1.04-2.24). Comparing frequency of charcoal use, those who use charcoal sometimes or often are more likely to have CHD, HBP, HC, and diabetes as compared to those who never use charcoal. The family members of charcoal users also had a significant increase of HC and stroke. When using TWC as an indicator for smoke exposure, it was found that those who always had TWC had significantly increased risk of stroke (OR=2.16; 95%CI 1.08-4.32), and those with sometimes TWC had a CHD risk (OR=2.64; 95%CI 1.02-6.81). Regarding kitchen location, the family members of cooks having kitchens both inside and outside a house had an elevated risk of stroke (OR=4.60; 95%CI 1.14-18.54).
This study presented an association between cardiovascular diseases and exposure to smoke from biomass, mainly charcoal, which is relatively cleaner when compared to wood, coal, or dung, a biomass which were often found in the literature. The study also showed that biomass use not only affects household cooks but also their family members. It was found that biomass users have a higher prevalence of HBP and HC, and their family members had a higher prevalence of HBP, HC, diabetes, and CHD (Table 3). Further analysis using logistic regression and control for potential confounder showed a significant OR of biomass use and CHD(F), HBP(F), HC(F), and diabetes(F) (Table 4). Compared to LPG, wood use also had a strong association with stroke (OR=7.64; 95%CI 1.18–49.61). Among charcoal users, those who use it sometimes or often had an elevated risk of CHD, HBP, HC, and diabetes for themselves, and risk of HC and stroke for their family members. The results are consistent with the literature. Previous research found biomass smoke contains a lot of pollutants, especially fine particulates, and carbon monoxide which are known to cause cardiovascular effects2. In laboratory studies, biomass smoke exposure was associated with endothelial inflammation23.
For hypertension, we found both cooks and their family members have a higher prevalence of HBP (Table 3). Further analysis indicated an elevated risk of HBP (OR= 1.61; 95%CI 1.10–2.35) among family members of cooks using biomass for cooking (Table 4). As compared to those who never use it, cooks who sometimes use charcoal have twice the risk of HBP (OR=2.04; 95%CI 1.32–3.15) and those who use charcoal over twenty years have 1.38 times the risk of HBP (OR=1.38; 95%CI 1.01–1.89). In the literature, there is increasing evidence to link biomass smoke and HBP24,25. A study in Peru found that biomass users had an increased risk of both prehypertension (OR=5.0; 95%CI 2.6–9.9), and hypertension (OR=3.5; 95%CI 1.7–7.0)12. In Bangladesh, it was found that among rural women, each additional year of biomass smoke exposure could increase the risk of HBP by 61% (OR=1.61; 95%CI 1.16–2.22)26. In Bangladesh, it was found that among rural women, one additional year of biomass smoke exposure to increase risk of HBP by 61% (OR=1.61; 95%CI 1.16–2.22)13. Recent studies in Honduras also linked PM2.5 and black carbon exposure and HBP among women using traditional and improved stoves25.
The current study also found a higher prevalence of HC among cooks and their family members using biomass fuel (Table 3) with a significant OR of 2.74 (95%CI 1.66–4.53) for family members (Table 4). The result showed a difference in the risk of HC among those who use wood, charcoal, and LPG. This risk also varied particularly according to the frequency of charcoal use. Compared to nonusers, an elevated risk of HC was found among cooks who sometimes use charcoal (OR=2.04; 95%CI 1.32–3.15), and among those who use charcoal over 20 years (OR=1.73; 95%CI 1.22–2.44). Among cooks, every year of using charcoal will increase risk of HC by about 1% (OR=1.010; 95%CI 1.002–1.017). Risk of HC was also increased among family members of cooks who often use charcoal (OR=1.52; 95%CI 1.02–2.27). Though the evidence was limited, other studies have found an association between cholesterol and COPD, a disease often found among biomass users26. A study in Ghana also found a strong association between wood smoke exposure and several hematological and biochemical indices, including HC (OR=20.44; 95%CI 2.610–160.2)27. The higher OR might be explained by the difference in biomass types, which was found to be wood in other studies, while most of respondents in this study use charcoal which is relatively cleaner.
We found about 10% of the respondents had type 2 diabetes and the prevalence of the disease was higher among biomass users (Table 3). Logistic regression analysis revealed a significant risk of diabetes among cooks using charcoal sometimes (OR=2.09; 95%CI 1.17–3.73) as compared to the never user group (Table 4). Among family members of cooks, risk of diabetes was elevated by using biomass fuel (OR=1.88; 95%CI 1.03–3.46), and years of using charcoal (OR=1.013; 95%CI 1.001–1.024). Similar results have also been reported by several studies on the effect of particulate matter or traffic-related air pollutants on diabetes28. In addition, experimental studies may provide potential mechanisms, including glucose homeostasis, systemic inflammation, stress in the liver and endoplasmic reticulum, and alterations of mitochondrial and other adipose tissue29. Currently, epidemiological studies on the effect of indoor air pollution on diabetes are rare. A study of women in Honduras reported an association between the prevalence of prediabetes/diabetes and PM2.5 in kitchen biomass cooking stoves30. This was consistent with the results from a previous study from Shanghai Putuo, which also found an elevated risk of several cardiovascular diseases including diabetes (OR=2.48; 95%CI 1.59–3.86) among people using solid fuel at home14.
Those who use biomass for cooking had a risk of CHD 4.35 times (95%CI 0.10–18.97) of LPG users; and those using charcoal sometimes had risk of CHD 4.11 times (95%CI 1.40–12.11) of never user group. These results are consistent with evidence from cigarette smoke and ambient air pollution. In animal studies, biomass fuel smoke caused arteriosclerotic effects in animal blood vessels11. Studies found COPD as a risk factor of CHD31; and our previous study found elevated chronic symptoms, such as chronic cough, dyspnea and runny nose which is a sign of COPD among cooks using biomass fuel for cooking26. Epidemiological studies also reported an association between solid fuel smoke exposure and CHD32. A study in Pakistan found that rural women who currently use solid fuel had an increased risk of acute coronary syndrome (OR=4.8; 95%CI 1.5–14.8)33. This is consistent with a study from Shanghai Putuo, which found solid fuel use in the home is associated with CHD (OR=2.58; 95%CI 1.53–4.32)14, and study from Shanxi, China found an elevated risk of CHD (OR=2.25) among solid fuel users15.
In this study, respondents who use wood (OR=7.64; 95%CI 1.18–49.61) and charcoal (OR=2.03; 95%CI 0.58–7.09) had an elevated risk of stroke as compared to clean fuel users (Table 4). Among charcoal users, those using charcoal sometimes (OR=1.66; 95%CI 0.44–6.29) and often (OR=2.76; 95%CI 0.56–13.50) seem to have a higher risk of stroke but a significant elevation was found only among the family members of cooks using charcoal often (OR=3.17; 95%CI 1.04–9.71). This was consistent with the literature. The association between household solid fuel use and stoke were also reported in a study from Shanghai Putuo (OR=1.87; 95% CI 1.03–3.38)14, and study from Shanxi, China (OR=1.64)15. In ambient settings, a long-term effect of PM exposure on cardiovascular disease, including stroke, was well established34. It was estimated that for each 10 µg/m3 increment in PM10, risk of overall stroke events will increase by 1.06 times (95%CI 1.02–1.11), and the risk of stoke mortality by 1.08 times (95%CI 0.99–1.18)35.
One potential drawback of this study was the use of self-reported data of diseases. Without the confirmation of medical records, the survey diseases are subjected to information bias. However, the bias will be distributed equally to all comparison groups, and this tends to underestimate the result. The number of participants included in this study was also rather small to detect the actual association of a rare disease, e.g. stroke. By using cross-sectional design, the study result cannot explain the causal relationship, because it is not known whether exposure or the disease occurred first. However, the problem is minimal for rare diseases.
The results from this study support research findings in other part of the world that using biomass for cooking increases the risk of cardiovascular diseases. This study also confirms the negative effects of using charcoal, which is considered to be a relatively cleaner fuel as compared with wood, dung, coal, and other agricultural residues. Concerned organizations should pay more attention to the issue and promote clean fuel usage.
Figshare: Household cooking and cardiovascular diseases, https://doi.org/10.6084/m9.figshare.12117066.v222.
This project contains the following underlying data:
Figshare: Questionnaire-household cooking and cardiovascular disease, https://doi.org/10.6084/m9.figshare.12121887.v221.
This project contains the following extended data:
Questionnaire-household cooking and cardiovascular disease.docx (Study questionnaire in English)
Questionnaire-household cooking and cardiovascular disease-Thai.docx (Study questionnaire in Thai)
Data are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).
We would like to thank the participants in this study. Our appreciation also goes to local health promoting hospitals in Phitsanulok and the village health volunteers for data collection. We would like also to thank Mr. Kevin Mark Roebl of the Division of International Affairs and Language Development, Naresuan University for editing assistance.
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Is the work clearly and accurately presented and does it cite the current literature?
Yes
Is the study design appropriate and is the work technically sound?
Partly
Are sufficient details of methods and analysis provided to allow replication by others?
Partly
If applicable, is the statistical analysis and its interpretation appropriate?
Partly
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Non communicable disease, Laboratory medicine, Public health
Is the work clearly and accurately presented and does it cite the current literature?
Yes
Is the study design appropriate and is the work technically sound?
Yes
Are sufficient details of methods and analysis provided to allow replication by others?
Yes
If applicable, is the statistical analysis and its interpretation appropriate?
I cannot comment. A qualified statistician is required.
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Public Health, Nutrition Epidemiology, Cardiovascular risk factors
Alongside their report, reviewers assign a status to the article:
Invited Reviewers | |||
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Version 2 (revision) 08 Oct 20 |
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Version 1 29 Apr 20 |
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