The association between a pro-inflammatory diet and brain age in middle-aged and older adults

Pro-inflammatory diets are associated with cognitive decline and dementia, but their impact on brain aging is unclear. We investigated the association between a pro-inflammatory diet and brain age, taking into account age, genetic risk for dementia, and systemic inflammation. UK Biobank participants (N = 21,473) aged 40-70 years and free of neurological disorders were included. The Dietary Inflammatory Index (DII) was calculated from participants' average intake of 31 nutrients, assessed up to five times via 24-h recalls. Participants were categorized into four DII groups (group 1, anti-inflammatory, DII < -2; group 2, DII -2 to < 0; group 3, DII 0 to < 2; group 4, DII ≥ 2), with group 4 reflecting the most pro-inflammatory diet. Brain age was estimated using a machine learning model based on 1079 structural and functional MRI measures, obtained approximately 9 years after baseline. We calculated brain age gap (BAG; brain age minus chronological age), where BAG > 0 reflects a biologically older brain than chronological age. An Alzheimer's disease polygenic risk score (PRS_AD), APOE4 status, and a composite score of systemic inflammation (INFLA-score) were determined from baseline blood samples. More pro-inflammatory diets were associated with increasingly greater BAG, with advanced brain age by [Formula: see text]=0.50 [95% CI 0.20, 0.80] years among those in group 4. There were no interactions between DII and age, PRS_AD, or APOE4 in relation to BAG, but associations were stronger among adults ≥ 60 years. INFLA-score mediated 8% of the DII-BAG association. These findings suggest that a pro-inflammatory diet may accelerate brain aging, especially in older adults.