Background/Objectives: Long COVID-19 (LC) has been associated with persistent inflammation and impaired vascular health. Dietary minerals are involved in oxidative stress, endothelial homeostasis, and arterial stiffness; however, their relationship with vascular health in LC remains poorly explored. This study aimed to examine the association between energy-adjusted dietary mineral intake and markers of vascular stiffness and vascular aging in adults with LC, while exploring potential sex-specific patterns. Methods: A total of 304 adults with LC from the BioICOPER study were included. Dietary mineral intake was assessed using a validated 7-day dietary record from the EVIDENT tool and expressed as mineral density per 1000 kcal for the regression analyses. Vascular assessment included carotid intima-media thickness (cIMT), carotid-femoral pulse wave velocity (cfPWV), brachial-ankle pulse wave velocity (baPWV), and the vascular aging index (VAI). Hierarchical multivariable linear regression models, false discovery rate (FDR) correction, restricted cubic spline analyses, sensitivity analyses excluding supplement users, and formal sex × mineral interaction tests were performed. Results: In descriptive adequacy analyses, adequate iron intake was associated with lower baPWV. In energy-adjusted linear regression models, no mineral-outcome association remained statistically significant after FDR correction. In the fully adjusted sensitivity model, zinc density showed a nominal positive association with cfPWV, but this association did not survive FDR correction. Restricted cubic spline analyses suggested possible non-linear associations of magnesium and potassium density with cfPWV and VAI. Formal interaction analyses did not provide robust evidence of sex-related effect modification. Conclusions: After energy adjustment and correction for multiple testing, the evidence for independent linear associations between dietary mineral density and vascular outcomes in adults with LC was limited. These exploratory findings suggest that mineral intake, dietary sources, and non-linear patterns deserve further evaluation in prospective studies and nutritional intervention trials.
