Does reported sex modify the association between ambient air pollution exposure and Alzheimer's disease and related dementias? A systematic review and meta-analysis.

In 30 seconds

This systematic review and meta-analysis examined whether reported sex modifies associations between ambient air pollution and dementia outcomes in longitudinal studies. It included 24 cohort studies involving more than 126 million participants and assessed 12 pollutants. No statistically significant female-to-male difference was found for Alzheimer’s disease or vascular dementia, or for most pollutants in overall dementia. The exception was PM2.5 in overall dementia, for which the pooled female-to-male ratio of risk ratios was 1.046 (95% CI: 1.024-1.069). The authors rated the evidence as moderate and cautioned that methodological heterogeneity and biases may obscure differences.

Key findings

• For PM2.5 and overall dementia, the pooled female-to-male ratio of risk ratios was 1.046 (95% CI: 1.024-1.069).
• For PM2.5 and Alzheimer’s disease, the pooled female-to-male ratio of risk ratios was 0.963 (95% CI: 0.919-1.009).
• For PM2.5 and vascular dementia, the pooled female-to-male ratio of risk ratios was 1.003 (95% CI: 0.954-1.054).
• The review included 24 cohort studies with more than 126 million participants; certainty of evidence was rated moderate.

Why it matters

Whether pollution-related dementia risks differ by sex could inform how population-level prevention is designed. These pooled findings do not show consistent modification by reported sex across dementia outcomes and pollutants, although the PM2.5 result for overall dementia suggests a possible difference. The authors’ caution about methodological heterogeneity and bias is important when interpreting that signal.

What to keep in mind

The authors note methodological heterogeneity and biases that may mask true differences. Heterogeneity was higher for PM10 in Alzheimer’s disease (I 2 = 73%).