Adherence to the Mediterranean diet, particularly olive oil intake, and metabolic health parameters are independently associated with SARS-CoV-2 vaccine-induced IgG responses.

Background: Determinants of SARS-CoV-2 vaccine-induced humoral immunity extend beyond vaccination and infection history; however, the role of specific dietary patterns and metabolic health parameters has not been fully elucidated. Although very few recent studies have examined the association between Mediterranean diet (MedDiet) and immune responses to SARS-CoV-2 vaccination, evidence integrating specific food components and detailed metabolic indices in relation to vaccine-induced humoral immunity is limited. The aim of the present study was to comprehensively evaluate the associations of MedDiet, its individual components and metabolic health parameters with SARS-CoV-2 vaccine-induced IgG responses in a well-characterized population of healthcare workers. Methods: In this cross-sectional study, 198 Greek healthcare workers (mean age 47.7 ± 11.6 years; 73.7 % female) who had received two or three BNT162b2 vaccine doses were evaluated 4-6 months post-vaccination. Demographic, clinical, anthropometric, metabolic and dietary data were collected at a single study visit. The MedDiet score and individual dietary components were assessed using a validated questionnaire. Serum SARS-CoV-2 anti-Spike (S) IgG levels were quantified using a standardized CMIA assay (Alinity i, Abbott). Multivariable linear regression analyses with log-transformed IgG titers as the dependent variable were performed using IBM SPSS Statistics. Results: The geometric mean titer of anti-S IgG was 6373.4 AU/mL (95 % CI 5190-7820). In adjusted models, prior SARS-CoV-2 infection (p < 0.001) and receipt of three vaccine doses (p = 0.007) were the strongest correlates of higher antibody levels. Higher MedDiet adherence was independently associated with increased IgG concentrations (p = 0.027). In models including dietary components, higher olive oil (p < 0.001) and legumes consumption (p = 0.032), and lower alcohol intake (p = 0.001) were significant positive determinants. METS-IR (Metabolic Score for Insulin Resistance) and 25OHD (25 hydroxyvitamin D) status showed a significant positive association with IgG levels [p = 0.042 and p = 0.060 (of borderline statistical significance), respectively], while smoking was inversely associated (p = 0.020). Importantly, the association with olive oil intake persisted in both infection-naïve and previously infected individuals. Conclusions: In this cross-sectional analysis, MedDiet adherence, particularly olive oil and legume consumption, and metabolic factors were associated with SARS-CoV-2 vaccine-induced IgG responses, highlighting the need for further longitudinal and interventional studies.