VITAMIN B12 INTERVENTION AND METABOLIC HEALTH IN ADULTS
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Background: Vitamin B12 is an essential cofactor in the one-carbon cycle, supporting DNA synthesis, mitochondrial energy production, and metabolic health. Current evidence links vitamin B12 deficiency to increased adiposity, adverse lipid profiles, and greater cardiometabolic risk. However, the effects of vitamin B12 intervention on metabolic health outcomes in adults have not been systematically evaluated. Methods: We searched for major scientific databases without restrictions on date or language and conducted a systematic review with meta-analysis. Results: Seventy-one trials with substantial variation in characteristics met the inclusion criteria, and thirty-eight trials provided relevant data. Compared with placebo or no intervention, vitamin B12 interventions were associated with lower BMI (-0.88 kg/m², 95%CI: -1.05, -0.71) and lower insulin resistance (-0.90, 95% CI: -1.55, -0.26). Compared with the same formula without vitamin B12, vitamin B12 interventions were associated with lower fasting blood glucose (-2.11 mg/dL, 95%CI: -3.69, -0.53), higher HDL cholesterol (3.72 mg/dL, 95%CI: 1.55, 5.90) and lower serum creatinine (-0.04 mg/dL, 95%CI: -0.07, -0.01). Both comparisons are associated with improved vitamin B12 status. In subgroup analyses of comparisons with placebo or no intervention in adults, total vitamin B12 differed by age, duration of intervention, form of vitamin B12, and baseline levels, while holo-transcobalamin differed by age and form of vitamin B12. Conclusions: Vitamin B12 interventions are associated with improved glycemic control, adiposity, and vitamin B12 status when compared with placebo or no intervention. They are also associated with improved glycemic control, lipid profile, vitamin B12 status, and kidney function when compared with the same formula without vitamin B12. Further randomized controlled trials are needed to clarify vitamin B12 interventions’ role in metabolic health and to evaluate the effects across different populations and administration routes.