Biomass fuel and coronary heart disease among women in Pakistan

Abstract

I investigated the risk of coronary heart disease (CHD) from indoor air pollution caused by use of biomass fuel for cooking. Following a systematic review of the relevant scientific literature, I conducted three linked studies among women in a rural region of Sindh, Pakistan.

The first was an investigation of levels of pollutants in kitchens and their determinants. 24-hour average concentrations of fine particulate matter (PM2.5) and carbon monoxide (CO) were measured in samples of households that used biomass or natural gas for cooking, and information was collected about other factors that might influence pollution levels. Associations with pollution were explored by regression modelling.

Secondly, a cross-sectional survey of cardiovascular morbidity was conducted in a sample of women aged 40 years or older who had used biomass fuel for cooking for at least the past year (n = 436), and a similar number of women (n=414) who had used natural gas for cooking for at least the past year. CHD was indicated by history of angina (Rose questionnaire), previous history of heart attack, and changes of CHD on electrocardiogram (ECG). Hypertension was assessed as a further outcome. Potential risk factors were ascertained by questionnaire and anthropometry. Associations between CHD outcomes and risk factors were assessed by logistic regression, adjusting for potential confounders.

The third study used a case-control design to determine the association of acute coronary syndrome (ACS) with use of biomass fuel. Women from a defined geographical area who were admitted to two public tertiary care hospitals in southern Sindh with ACS (n = 364) were identified prospectively, and compared with controls (n=727), matched for sex and age, who were admitted to the same hospitals for reasons other than ACS. Information about exposure to potential risk factors, including use of biomass fuel for cooking was ascertained through a questionnaire. Associations with risk factors were assessed by conditional logistic regression.

The first study found high average concentrations of CO and particularly PM2.5 in the kitchens of biomass-users. Ventilated kitchens tended to have lower levels of the pollutants, and houses with smokers somewhat higher concentrations. However, stove chimneys had no discernible impact on levels of PM2.5. In my cross-sectional survey, I found no association of hypertension or the three measures of CHD – angina, previous history of heart attack and definite or probable CHD on ECG - with current use of biomass for cooking. This may have been because of inaccuracies in the outcome measures, or because most users of natural gas had previously used biomass. In contrast, the case-control study found a clearly elevated risk of ACS among women who had ever used biomass for cooking, although not particularly with more recent use.

Overall, my findings add to the weight of evidence for an importantly increased risk of CHD from use of biomass for cooking, and are a further encouragement to initiatives aimed at reducing exposures to the indoor air pollution that it produces. However, they suggest that the full benefits from better design of stoves or switching to other fuels may not accrue until many years after the changes are introduced. Further studies are needed to clarify the relationship of cardiovascular morbidity to use of biomass fuel
These could perhaps be embedded in established cohort studies of cardiovascular disease and national surveys.

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Identifiers

ORCID for David Coggon: orcid.org/0000-0003-1930-3987

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