Association of Biochemical B12 Deficiency With Metformin Therapy and Vitamin B12 Supplements

Study answer

What this study found

Metformin therapy is associated with higher prevalence of biochemical B12 deficiency among adults with type 2 diabetes (adjusted OR 2.92; 95% CI 1.28-6.66) and borderline deficiency (OR 2.16; 95% CI 1.22-3.85). Vitamin B12 supplementation reduces risk of borderline deficiency in type 2 diabetes (OR 0.43; 95% CI 0.23-0.81) and reduces biochemical deficiency in those without diabetes (OR 0.26; 95% CI 0.17-0.38) and borderline deficiency (OR 0.27; 95% CI 0.21-0.35). Among diabetics on metformin using supplements, higher daily B12 doses (>6 mg) were associated with a marked reduction in…

Study & population

NHANES 1999-2006; nationally representative cross-sectional sample of U.S.

Intervention

Vitamin B12-containing supplements; daily intake categories: 0 mg (no supplement), 0-6 mg/day, 6-25 mg/day, >25 mg/day; duration not reported; taken as dietary supplement.

Key limitation

Cross-sectional NHANES design; cannot infer causality; metformin and supplement use relied on self-report; B12 status based on serum B12 with limited MMA data; missing data on some covariates; analysis restricted to adults ≥50 years; possible misclassification of diabetes type; generalizability limited to older adults.

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Original abstract