Global Prevalence of Vitamin B12 Deficiency

Background

Dr. Lindsay H. Allen from the USDA Western Human Nutrition Research Center at UC Davis conducted this comprehensive review examining global vitamin B12 deficiency prevalence. Published in the American Journal of Clinical Nutrition (PMID: 19116323).

Study Design

Systematic review of population-based studies examining B12 status across different age groups, geographic regions, and dietary patterns. Analyzed serum B12, methylmalonic acid (MMA), and homocysteine as markers of deficiency.

Key Findings

Population	Deficiency Prevalence
Elderly (>60 years)	10-15% in Western countries
Vegetarians/Vegans	25-86% depending on duration
Developing countries	Up to 40-80% in some regions
Pregnant women	Highly variable, often underdiagnosed

Key insight: Serum B12 alone underestimates true deficiency. MMA elevation indicates tissue-level depletion.

Mechanistic Insights

B12 deficiency develops in stages:

1. •Negative B12 balance (declining stores)
2. •B12 depletion (low holotranscobalamin)
3. •B12 deficiency (elevated MMA, declining serum B12)
4. •Clinical deficiency (anemia, neurological symptoms)

Clinical Implications

The review established that deficiency is far more common than previously recognized, particularly in vegetarians, elderly, and populations with limited animal food access. Early detection with MMA testing prevents irreversible neurological damage.

Metabolic Health Perspective

B12 status affects homocysteine metabolism (cardiovascular risk), methylation capacity (epigenetic regulation), and energy metabolism. Metabolic optimization requires levels well above the minimum to prevent deficiency (~500 pg/mL vs. lab cutoff of 200 pg/mL).