Association Between Vitamin B12 Deficiency and Anemia: A Systematic Review and Meta-Analysis

Background: Vitamin B12 deficiency is a well-recognized cause of anemia, particularly megaloblastic anemia. However, variability in diagnostic criteria and population characteristics has led to inconsistent estimates of its association with anemia.

Objective: To systematically evaluate and quantify the association between vitamin B12 deficiency and anemia through a meta-analysis of available studies.

Methods: A systematic search of PubMed, Scopus, Web of Science, and Cochrane Library was conducted for studies published up to March 2026. Observational studies reporting the prevalence or odds of anemia among individuals with vitamin B12 deficiency were included. Data were pooled using a random-effects model. Heterogeneity was assessed using I² statistics, and publication bias was evaluated using funnel plots and Egger’s test.

Results: A total of 22 studies involving 14,875 participants were included. Vitamin B12 deficiency was significantly associated with increased odds of anemia (pooled OR = 3.45; 95% CI: 2.60–4.58; p < 0.001). Subgroup analysis showed stronger associations in elderly populations and in developing countries. Moderate heterogeneity was observed (I² = 56%). No significant publication bias was detected.

Conclusion: Vitamin B12 deficiency is strongly associated with anemia, particularly in vulnerable populations. Early detection and intervention are crucial to reduce morbidity.