Association between cooking fuels and mild cognitive impairment in older adults from six low- and middle-income countries

Principle results

In this large representative sample of adults aged from six LMICs, unclean cooking fuel (vs. clean cooking fuel) was associated with a 1.48 (95% CI = 1.08, 2.03) times higher for the MCI. The associations were similar between men and women. Additionally, when studying kitchen ventilation, the absence of a chimney or hood was associated with significantly higher odds of MCI (OR = 1.88; 95% CI = 1.25, 2 ,84). To our knowledge, this is the first study of impure cooking fuel use and MCI.

Results interpretation

The results of the current study are consistent with previous studies of indoor cooking fuel and general cognitive decline from China and Mexico.7,10,11,12,13,14. Additionally, in a recent systematic review looking at air pollution and dementia risk, comprising 13 studies, it was observed that greater exposure to particulate matter, nitrogen dioxide, nitrogen oxides and carbon monoxide were all associated with an increased risk of dementia.27.

There are several plausible pathways that may explain the relationship between impure cooking fuel and the MCI observed in our study. These pathways likely act via an increase in indoor air pollutants (i.e. particulates) from impure cooking fuels. These pollutants induce systemic inflammation and oxidative stress, which can affect the central nervous system via the circulatory system, or translocation via the olfactory nerve. Inflammatory responses in brain areas, mediated by cytokines, chemokines or oxidative stress, can lead to aberrant protein aggregation, impaired neurotransmitter and neurotrophin signaling, neuronal remodeling and neurodegeneration, which are the main causes of cognitive impairment.7.28. In addition, oxidative damage is implicated in the mechanisms of neurodegeneration8. Next, an increase in air pollutants was found to be associated with a smaller total brain volume and a higher risk of hidden cerebral infarction.9 which are associated with neurological abnormalities, lower cognitive functioning and the onset of dementia7.29.

Interestingly, previous studies have identified a stronger association between the use of unclean cooking fuels and the risk of cognitive decline in women compared to men.12.13, but the present study found no significant gender interaction in the cooking fuel/MCI association. Previous research has suggested that women’s cognitive functions may be more sensitive to the dangerous effects of indoor particles due to differences in sex hormones and neuroimmune responses to toxins.12. However, the present study suggests that this potentially higher female susceptibility to particles may not extend to MCI. Clearly, further research is needed to determine whether gender is an effect modifier in the association between the use of impure cooking fuels and MCI.

Implications of the results

The findings of this study directly support the implementation of United Nations Sustainable Development Goal (SDG) 7 “Ensure access to affordable, reliable, sustainable and modern energy for all”30, which covers reducing the use of impure cooking fuels and indirectly contributes to achieving 10 of the 17 SDGs. Specifically, international bodies such as the WHO are recommending actions such as government commitment to prioritizing clean cooking solutions, mobilizing funding to scale up promising businesses, cross-sector collaboration, and monitoring of consumption of clean cooking. household energy.31. Importantly, the use of impure cooking fuels has been shown to be associated with multiple negative health effects including, for example, respiratory disease, cardiovascular disease, cataracts and depression.32,33,34. The results of the present study show that eliminating impure cooking fuels may also have the added benefit of contributing to the prevention of MCI and possibly dementia.

In addition, the present results also suggest that the installation of appropriate cooking ventilation devices (i.35which in turn can help promote overall household health and prevent health problems, including MCI.

Strengths and limitations

The large representative sample of older adults from multiple LRICs is an obvious strength of the present study. However, the results should be interpreted in light of the limitations of the study. First, the study is cross-sectional in nature and therefore temporal associations cannot be determined. Clearly, more longitudinal studies on this topic are needed. Second, the majority of questions were self-reported. Therefore, it is possible that recall and social desirability biases were introduced into the results. Second, the present study lacked information on the duration of exposure to impure cooking fuel. This information should be taken into account in future studies, as exposure is likely to increase throughout life. For example, autopsy studies of children and young adults living in Mexico City have found associations between exposure to urban air pollution and particle deposition or inflammation in the brain.28.36. Second, since the study was not designed to generate clinical diagnoses of dementia, our sample could have included people with mild dementia. However, the prevalence of MCI in our study was within the previously reported numbers37. In addition, we were unable to perform analyzes by country because stable estimates could not be obtained due to limited sample size and lack of statistical power in each country. Thus, future multi-country studies with a larger sample size should assess whether the associations assessed in our study differ across countries. Finally, this study did not collect dietary data. The choice of cooking fuel used may depend on the type of food. Indeed, certain diets have been associated with a higher risk of MCI.38 and therefore may have introduced some bias into the results.

Andrew B. Reiter