What is the prevalence of concurrent vitamin B12 and iron deficiencies?

Prevalence of Concurrent Vitamin B12 and Iron Deficiency

Concurrent vitamin B12 and iron deficiency is relatively uncommon in the general population, but specific high-risk groups show substantially elevated rates—particularly pregnant women (where up to 18.6% have iron deficiency), vegetarians/vegans (where B12 deficiency reaches 45% in infants and up to 86.5% in adults), and post-bariatric surgery patients.

Population-Specific Prevalence Data

General Population

• Iron deficiency alone is far more common than concurrent deficiencies. In pregnant women in the United States, iron deficiency prevalence is estimated at 18.6%, with 16.2% of those also having anemia 1
• The overall prevalence ranges from 2% to 27% depending on trimester and ethnicity, with higher rates in later trimesters and minority populations (Non-Hispanic Black and Mexican American women) 1

High-Risk Populations for Concurrent Deficiency

Vegetarians and Vegans:

• B12 deficiency prevalence reaches 45% in infants, 0-33.3% in children/adolescents, 17-39% in pregnant women (trimester-dependent), and 0-86.5% in adults and elderly 2
• Vegans show higher deficiency rates than other vegetarian subtypes 2
• These populations often have concurrent iron deficiency due to limited bioavailable iron from plant-based diets 2

Post-Bariatric Surgery Patients:

• This group faces exceptionally high risk for both deficiencies due to reduced gastric acid production, decreased intrinsic factor availability, and malabsorption 3
• B12 stores can last 2-3 years, so deficiency may present gradually 3

Inflammatory Bowel Disease (IBD):

• Multiple concurrent deficiencies are common, with both iron deficiency anemia and B12/folate deficiencies occurring together 1
• Risk relates directly to disease activity and intestinal inflammation 1

Important Clinical Context

Why Concurrent Deficiency Appears Less Common Than Expected

Biochemical evidence doesn't always translate to clinical anemia:

• High prevalence of biochemical B12 or folate deficiency does not produce a comparable prevalence of anemia 4
• The overall contribution of B12 deficiency to global anemia burden is probably not significant, except in vegetarian communities 4

Iron deficiency can mask B12 deficiency:

• Iron deficiency anemia may coexist with B12 and folate deficiency, confounding hematological features and causing underestimation of vitamin deficiency prevalence 4
• Only 18.9% of patients with confirmed B12 deficiency meet WHO criteria for pernicious anemia 5

Interrelated metabolism:

• Treatment of iron deficiency anemia with pharmacological iron significantly increases serum B12 and folate levels, even in patients with baseline low B12 (<200 pmol/L) 6
• This suggests iron deficiency affects multiple metabolic pathways, including B12 and folate metabolism 6

Risk Factors for Concurrent Deficiency

Dietary factors:

• Vegetarian/vegan diet lacking both iron-rich foods and B12 sources 1, 2
• Short interval between pregnancies 1

Malabsorption conditions:

• Gastrointestinal disease affecting absorption 1
• Celiac disease 7
• Inflammatory bowel disease (especially with ileal involvement or resection) 1
• Post-bariatric surgery status 3

Medications affecting both nutrients:

• Antacids and H2 receptor antagonists (reduce iron and B12 absorption) 1, 3
• Metformin (B12 deficiency risk, especially >4 months use) 3
• Anticonvulsants, sulfasalazine, methotrexate (affect folate/B12) 1, 3

Critical Clinical Pitfalls

Don't rely solely on serum levels:

• Standard total B12 tests may not reflect biologically active B12 available for cellular use 3
• Up to 50% of patients with "normal" serum B12 have metabolic deficiency when measured by methylmalonic acid (MMA) 3
• Consider measuring active B12 (holotranscobalamin) or MMA when clinical suspicion remains high despite normal total B12 3

Screen high-risk populations proactively:

• Annual B12 and folate screening for patients with small bowel disease, ileal resection, or post-bariatric surgery 1
• More frequent monitoring in extensive small bowel resection or extensive ileal Crohn's disease 1

Treat B12 deficiency before giving folate:

• Folate supplementation may mask severe B12 depletion and precipitate subacute combined degeneration of the spinal cord 1
• Always check and treat B12 deficiency before initiating folic acid treatment 1