Hypertension And Stroke Do Not Significantly Modify Association Of Air Pollution With Dementia

Fine particulate matter air pollution (PM2.5) has been consistently linked to cardiovascular disease, which is itself associated with a higher risk of dementia. A recent study published in JAMA Network Open by Boya Zhang and colleagues at the University Of Michigan School Of Public Health aimed to explore whether hypertension and stroke act as mediators or modifiers in the relationship between PM2.5 exposure and incident dementia.

The study utilised data from the Environmental Predictors of Cognitive Health and Aging (EPOCH) Project, drawing from biennial surveys conducted between 1998 and 2016 as part of the Health and Retirement Study (HRS) in the US. The analysis focused on participants aged 50 and older without dementia at baseline, with complete data on PM2.5 exposure, potential mediators (hypertension and stroke), outcomes, and demographic factors.

The findings of the study were:

• Among the 27,857 participants (mean age 61 years; 56.5% female; 69.1% non-Hispanic White), 14.7% developed dementia during the follow-up period (mean 10.2 years).
• Over half of those with dementia had hypertension at baseline, while 9.4% received a hypertension diagnosis during follow-up. Additionally, 9.2% had a history of stroke at baseline, and 16.4% experienced stroke during the follow-up period.
• Baseline PM2.5 concentrations ranged from 10.9 to 14.9 μg/m3 (interquartile range).
• In fully adjusted models, there was no significant association between higher PM2.5 levels (per interquartile range) and an increased risk of incident dementia (HR 1.04; 95% CI 0.98-1.11).
• While prevalent stroke (HR 1.67; 95% CI 1.48-1.88) and hypertension (HR 1.15; 95% CI 1.08-1.23) were positively associated with incident dementia compared to those without stroke and hypertension during follow-up, PM2.5 exposure showed no significant association with stroke (odds ratio per interquartile range increment in PM2.5, 1.08; 95% CI 0.91-1.29) and no evidence of an association with hypertension (odds ratio per interquartile range increment in PM2.5, 0.99; 95% CI 0.92-1.07).
• Consequently, hypertension and stroke did not appear to act as mediators or modifiers in the relationship between PM2.5 exposure and incident dementia.

These findings suggest that while hypertension may increase individuals' susceptibility to air pollution, it does not significantly mediate or modify the association between PM2.5 exposure and dementia. Further research is needed to explore alternative pathways and potential mediators of this risk.

Reference:

Zhang, B., Langa, K. M., Weuve, J., D’Souza, J., Szpiro, A., Faul, J., Mendes de Leon, C., Kaufman, J. D., Lisabeth, L., Hirth, R. A., & Adar, S. D. Hypertension and stroke as mediators of air pollution exposure and incident dementia. JAMA Network Open,2023;6(9),e2333470. https://doi.org/10.1001/jamanetworkopen.2023.33470