Associations of Mediterranean Diet Adherence with Cardiometabolic Outcomes, Psychological Symptoms, and Health-Related Quality of Life Among Adults Attending Primary Care Centres in Navarra, Spain: A Cross-Sectional Study

Background/Objectives: Mediterranean diet adherence has been associated with cardiometabolic and psychological health, but evidence integrating these outcomes with health-related quality of life in primary care populations remains limited. This study examined the associations between Mediterranean diet adherence and anthropometric, cardiometabolic, psychological, and health-related quality-of-life outcomes. Methods: This cross-sectional study included 495 adults attending primary care centres in Navarra, Spain. Mediterranean diet adherence was assessed using the validated 14-item Mediterranean Diet Adherence Screener (MEDAS-14). Multivariable linear regression models examined associations between the continuous MEDAS-14 score and study outcomes, adjusting for age, sex, educational attainment, physical activity, and BMI when appropriate. Sensitivity analyses, assessment of non-linearity, false-discovery-rate correction across the nine principal outcomes, and interaction-by-sex analyses were also performed. Results: Each one-point increase in the MEDAS-14 score was associated with lower systolic blood pressure (β = −1.056 mmHg; 95% confidence interval (CI): −1.774 to −0.338; p = 0.004), diastolic blood pressure (β = −0.838 mmHg; 95% CI: −1.261 to −0.415; p < 0.001), fasting blood glucose (β = −0.745 mg/dL; 95% CI: −1.365 to −0.125; p = 0.019), and Goldberg anxiety score (β = −0.249; 95% CI: −0.368 to −0.130; p < 0.001), and with higher EQ VAS scores (β = 1.224; 95% CI: 0.570 to 1.878; p < 0.001). The associations with BMI, systolic and diastolic blood pressure, fasting blood glucose, Goldberg anxiety score, and EQ VAS remained statistically evident after false-discovery-rate correction, and the overall pattern was generally consistent across sensitivity analyses. No adjusted association with Goldberg depression score was observed. BMI was inversely associated with MEDAS-14 in the principal linear model (β = −0.299 kg/m2; 95% CI: −0.521 to −0.077; p = 0.009), whereas the association with waist circumference was not statistically significant (β = −0.475 cm; 95% CI: −1.046 to 0.095; p = 0.102). BMI, waist circumference, and total cholesterol showed evidence of non-linearity. Exploratory interaction analyses showed evidence of interaction by sex for diastolic blood pressure and EQ VAS after false-discovery-rate correction. Conclusions: Higher MEDAS-14 scores were associated with lower blood pressure and fasting blood glucose, fewer anxiety symptoms, and better self-perceived health. Associations for BMI, waist circumference, and total cholesterol showed evidence of non-linearity and should be interpreted cautiously. These cross-sectional findings do not establish temporality or causality and should also be interpreted in light of the lack of adjustment for relevant clinical diagnoses and medication use. Prospective confirmation is warranted.