A month ago, my classmate Cherie blogged about the links between air pollution and cognitive decline (check out her post here). In this entry, I hope to expand upon her findings by discussing how varying groups of people may have their cognitive abilities affected differently by air pollution.
Chandra et al. (2022) highlights that air pollution adversely affects humans’ cognitive capabilities throughout their life course, starting even before birth. Their studies on prenatal and postnatal exposure (to air pollution) yielded associations with adverse impacts on cognitive skills, adaptive functioning, and behavioural indices among children. Despite the absence of conclusive studies on the cognitive impacts of air pollution in low and lower-middle income countries (LICs and LMICs) , the authors suggest that greater dependence on wood stoves for cooking may translate to relatively more severe indoor air pollution and thus poorer cognitive abilities among adults in LICs and LMICs.
Yet, the impacts of air pollution on adults in high and higher-middle income countries (HICs and HMICs) are also differentiated based on the “aetio-pathogenic” pathways of air pollution that accounts for various lifestyle factors and circumstances, culminating in spatially and temporally heterogeneous patterns of cognitive impairment.
Figure 1. Aetio-pathological pathways of air pollution during one’s life course (Chandra et al., 2022)
Ailshire and Clarke (2014) highlight how exposure to fine particulate matter impacts the cognitive function of elderly adults in the US. Among a sample of respondents whose average exposure to PM2.5 was greater than the national ‘safe’ threshold, they observed that cognitive decline was most severe among the oldest respondents. These findings are compounded by the work of Wellenius et al. (2012), who demonstrate the negative relationship between residential distance to major roads and cognitive decline for elderly adults above the age of 65. As illustrated by Figure 2, a decrease in residential distance to major roadway (closer proximity to air pollution) is accompanied by poorer performance in all cognitive function tests with the exception of ‘Recognition’.
Figure 2. Table illustrating the change in cognitive test scores following a decrease in residential distance to major roadway (Ailshire and Clarke, 2014)
A final study by Kim et al. (2019) investigates the significance of gender as a confounder in the relationship between air pollution and cognitive decline. I found it interesting to compare this study with the one by Ailshire and Clarke (2014) discussed earlier in this post. With reference to Figure 3, the proportion of men aged above 65 was approximately 10% greater than the proportion of women aged above 65. In line with Ailshire and Clarke (2004)’s findings, this should have translated into greater cognitive decline among the men who were generally older than the women. Yet, the researchers concluded that exposure to particulate matter posed a higher risk of cognitive decline to women than men. Moreover, living in metropolitan areas should theoretically imply shorter distances to traffic networks and greater exposure to air pollution. However, the data in Figure 4 proves otherwise. As shown, men were more at risk if they lived in non-metropolitan areas.
Figure 3. Table of selected characteristics among study participants (Kim et al., 2019)
Figure 4. Table illustrating the odds of declining cognitive function associated with exposure to air pollutants by gender and geographic location of residence (Kim et al., 2019)
This brief comparison suggests that a whole wide spectrum of other confounders are at play, and that the matter at hand cannot be simply reduced to a few variables such as age or gender. More than ever, we should continue to strive towards curbing air pollution so that vulnerable groups and communities do not have to suffer the consequences.
Until the next entry, breathe safe and be safe!
References
Ailshire, J. A., & Crimmins, E. M. (2014). Fine particulate matter air pollution and cognitive function among older US adults. American Journal of Epidemiology, 180(4), 359–366. https://doi.org/10.1093/aje/kwu155
Chandra, M., Rai, C. B., Kumari, N., Sandhu, V. K., Chandra, K., Krishna, M., Kota, S. H., Anand, K. S., & Oudin, A. (2022). Air pollution and cognitive impairment across the life course in humans: A systematic review with specific focus on income level of study area. International Journal of Environmental Research and Public Health, 19(3), 1405. https://doi.org/10.3390/ijerph19031405
Kim, H., Noh, J., Noh, Y., Oh, S. S., Koh, S.-B., & Kim, C. (2019). Gender difference in the effects of outdoor air pollution on cognitive function among elderly in Korea. Frontiers in Public Health, 7, 1–10. https://doi.org/10.3389/fpubh.2019.00375
Wellenius, G. A., Boyle, L. D., Coull, B. A., Milberg, W. P., Gryparis, A., Schwartz, J., Mittleman, M. A., & Lipsitz, L. A. (2012). Residential proximity to nearest major roadway and cognitive function in community-dwelling seniors: Results from the mobilize Boston Study. Journal of the American Geriatrics Society, 60(11), 2075–2080. https://doi.org/10.1111/j.1532-5415.2012.04195.x