Prevalence of Vitamin B12 Deficiency and Its Association With Cognitive Performance Among Adolescents

Background: Vitamin B12 is required for one-carbon metabolism, myelin maintenance and normal neurologic function.Adolescence is a period of rapid growth and increasing academic demands, yet Indian data linking vitamin B12 status withcognitive performance remain limited. The study is designed to estimate the hospital-based prevalence of vitamin B12deficiency among adolescents and examine its association with cognitive performance and selected nutritional factors.Materials and Methods: A cross-sectional study was conducted in the Department of Pediatrics, Apollo Institute ofMedical Sciences and Research, Hyderabad, from June 2025 to May 2026. Adolescents aged 10-19 years were enrolled.Serum vitamin B12 was measured by chemiluminescence. Deficiency was defined as <200 pg/mL, borderline status as 200-299 pg/mL, and sufficient status as >=300 pg/mL. Cognitive performance was assessed using age-standardized Raven'sStandard Progressive Matrices and a standardized Digit Span task. A composite cognitive z-score was derived. Groupdifferences were tested with chi-square and one-way ANOVA, and multivariable logistic regression was used to identifyfactors associated with lower cognitive performance. Results: Among 252 adolescents, 79 had vitamin B12 deficiency,giving a prevalence of 31.3% (95% CI 25.9-37.3). Borderline status was present in 21.8%. Deficiency was substantiallymore frequent among vegetarians and adolescents consuming animal-source foods fewer than three times per week (bothp<0.001), and it was also associated with anemia (p=0.008). Mean composite cognitive scores increased across deficient,borderline and sufficient vitamin B12 categories (-0.36, -0.03 and 0.25, respectively; ANOVA p<0.001). Serum vitamin B12correlated positively with the composite cognitive score (r=0.39, p<0.001). After adjustment, deficient status remainedassociated with lower cognitive performance (adjusted OR 5.83, 95% CI 2.30-14.76). Conclusion: Vitamin B12 deficiencywas common in this hospital-based adolescent sample and was associated with poorer cognitive performance. Predominantlyvegetarian dietary patterns and infrequent intake of animal-source foods identified adolescents at higher risk. These findingssupport nutritional screening in appropriate clinical settings, while longitudinal studies are needed before causal inferencescan be made.