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Background:

Previous studies suggest that certain dietary patterns and constituents may be beneficial to brain health. Airborne exposures to fine particulate matter [particulate matter with aerodynamic diameter $\le 2.5\mathrm{\mu }\mathrm{m}$ (${\mathrm{PM}}_{2.5}$)] are neurotoxic, but the combined effects of dietary patterns and ${\mathrm{PM}}_{2.5}$ have not been investigated.

Objectives:

We examined whether previously reported association between ${\mathrm{PM}}_{2.5}$ exposure and lower white matter volume (WMV) differed between women whose usual diet during the last 3 months before baseline was more or less consistent with a Mediterranean–DASH Intervention for Neurodegenerative Delay (MIND)-like diet, a dietary pattern that may slow neurodegenerative changes.

Methods:

This study included 1,302 U.S. women who were 65–79 y old and free of dementia in the period 1996–1998 (baseline). In the period 2005–2006, structural brain magnetic resonance imaging (MRI) scans were performed to estimate normal-appearing brain volumes (excluding areas with evidence of small vessel ischemic disease). Baseline MIND diet scores were derived from a food frequency questionnaire. Three-year average ${\mathrm{PM}}_{2.5}$ exposure prior to MRI was estimated using geocoded participant addresses and a spatiotemporal model.

Results:

Average total and temporal lobe WMVs were $0.74{\mathrm{cm}}^3$ [95% confidence interval (CI): 0.001, 1.48) and $0.19{\mathrm{cm}}^3$ (95% CI: 0.002, 0.37) higher, respectively, with each 0.5-point increase in the MIND score and were $4.16{\mathrm{cm}}^3$ (95% CI: $–6.99$, $–1.33$) and $1.46{\mathrm{cm}}^3$ (95% CI: $–2.16$, $–0.76$) lower, respectively, with each interquartile range (IQR) ($\text{IQR}=3.22{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$) increase in ${\mathrm{PM}}_{2.5}$. The inverse association between ${\mathrm{PM}}_{2.5}$ per IQR and WMV was stronger ($p\text{-interaction}<0.001$) among women with MIND scores below the median (for total WMV, $–12.47{\mathrm{cm}}^3$; 95% CI: $-17.17$, $-7.78$), but absent in women with scores above the median ($0.16{\mathrm{cm}}^3$; 95% CI: $-3.41$, 3.72), with similar patterns for WMV in the frontal, parietal, and temporal lobes. For total cerebral and hippocampus brain volumes or WMV in the corpus callosum, the associations with ${\mathrm{PM}}_{2.5}$ were not significantly different for women with high MIND scores and women with low MIND scores.

Discussion:

In this cohort of U.S. women, ${\mathrm{PM}}_{2.5}$ exposure was associated with lower MRI-based WMV, an indication of brain aging, only among women whose usual diet was less consistent with the MIND-like dietary pattern at baseline. https://doi.org/10.1289/EHP8036