B12 Deficiency Causes & Risk Factors
B12 deficiency is rarely caused by one issue alone. Intake, absorption, medication exposure, autoimmune disease, and age-related change can overlap, so identifying the full picture is essential for safe long-term care.
Seek Urgent Clinical Advice If You Notice
- New numbness, balance loss, or rapidly progressive weakness.
- Acute confusion, severe memory change, or major mood deterioration.
- Symptoms worsening despite ongoing treatment and adherence.
Appointment Preparation
Bring this checklist to help your clinician identify likely causes faster.
- Bring a dated symptom timeline including neurological, cognitive, and fatigue changes.
- List all medications, supplements, and any recent changes to dose or frequency.
- Ask what likely cause is being investigated, not only whether levels are in range.
- Discuss whether additional markers or repeat testing are needed if symptoms persist.
- Agree a clear follow-up plan with timeframe, treatment goals, and safety-net advice.
Risk Factor Clusters
Autoimmune and Gastric Causes
Immune attack on stomach cells can reduce intrinsic factor and block B12 absorption over time.
Common Examples
- Pernicious anaemia
- Autoimmune gastritis
- Family history of autoimmune disease
Dietary and Intake Factors
Low intake can develop gradually, especially when there is limited use of animal foods or fortified products.
Common Examples
- Long-term vegan or vegetarian diets
- Low appetite or restrictive eating patterns
- Inadequate fortified food intake
Gut and Absorption Conditions
Inflammation, surgery, or gut disorders can reduce B12 uptake even when intake is adequate.
Common Examples
- Coeliac disease
- Crohn's disease
- History of gastric or ileal surgery
Medication-Related Risk
Some long-term medications can affect B12 status and should be reviewed in context of symptoms.
Common Examples
- Metformin
- Proton pump inhibitors
- Long-term acid suppression
Ageing and Physiological Change
Older adults can have reduced stomach acid, making food-bound B12 harder to absorb.
Common Examples
- Age over 60
- Frailty or low dietary variety
- Multiple chronic conditions
Core Causes At A Glance
Pernicious Anaemia
Pernicious anaemia is an autoimmune process that damages gastric cells and can reduce intrinsic factor, a protein needed for B12 absorption. It is a common driver of persistent deficiency and should be considered when symptoms recur despite dietary improvement.
Dietary Causes
Because B12 is concentrated in animal foods and fortified products, low intake can emerge in vegan or vegetarian patterns without planned supplementation. Reduced appetite, restrictive eating, and food insecurity can also increase risk.
Absorption Problems
Absorption may fail even with adequate intake. Coeliac disease, Crohn's disease, inflammatory bowel conditions, bacterial overgrowth, and surgery involving the stomach or ileum can all reduce B12 uptake.
Medications
Long-term use of metformin and acid-suppressing medications can contribute to B12 decline in some people. Risk is often cumulative and should be reviewed alongside symptoms, dose, and treatment duration.
Age-Related Factors
With age, reduced stomach acid can make food-bound B12 harder to absorb. Frailty, multimorbidity, and reduced dietary variety can further increase vulnerability in older adults.
Other High-Risk Groups
People with previous bariatric surgery, chronic gastrointestinal illness, alcohol dependence, or significant long-term malnutrition may need proactive monitoring. Pregnancy and breastfeeding can also increase nutritional demands and warrant early review if symptoms appear.
Why Cause Matters for Treatment
Understanding the underlying cause helps determine how long treatment should continue, what monitoring is needed, and how to prevent relapse. Cause-led care is usually more effective than relying on single blood results in isolation.
Next Step: Link Cause To Your Treatment Plan
Identifying why deficiency developed helps guide long-term monitoring and reduce relapse risk.