The Role of Age at Onset on the Clinical Course and Biochemical Parameters of Anorexia Nervosa

Background: Anorexia nervosa (AN) has the highest mortality rate among psychiatric disorders, making early diagnosis and tailored management crucial. This study aimed to evaluate the impact of age at onset (AAO)-childhood/adolescence versus adulthood-on the clinical course and associated biochemical parameters. Methods: Seventy-six female patients with AN were divided into two groups based on AAO (<18 years vs. ≥18 years). Group comparisons were performed using t-tests for continuous variables and χ² tests for categorical variables. Correlation analyses assessed associations between AAO and continuous variables. Significant findings were entered into regression models, including a binary logistic regression with AAO as the dependent variable and a linear regression with significant correlations as predictors. Results: The early-onset group showed significantly higher potassium levels and a lower sodium/potassium ratio (Na⁺/K⁺) compared with the late-onset group (potassium: t = 0.93, p < 0.01; Na⁺/K⁺: t = 3.39, p < 0.01). AAO was strongly inversely correlated with potassium levels (r = -0.75, p < 0.01) and positively correlated with cholesterol (r = 0.574, p < 0.01) and Na⁺/K⁺ (r = 0.78, p = 0.01). Binary logistic regression correctly classified 87% of cases, showing that lower Na⁺/K⁺ was associated with earlier onset (OR = 2.23, p = 0.03). Linear regression confirmed significant associations of AAO with cholesterol levels (B = 0.07, p = 0.02) and Na⁺/K⁺ (B = 1.68, p < 0.01). Conclusions: AAO in AN is strongly associated with specific biochemical parameters. Early-onset patients exhibit more severe electrolyte imbalances, while late-onset cases show higher cholesterol levels, suggesting increased cardiovascular risk. These findings emphasize the importance of personalized treatment approaches according to AAO, although further studies are warranted to confirm these results.