PPIs (omeprazole, lansoprazole) and B12: when to test, when to inject

The mechanism

Vitamin B12 in food is bound to animal protein. Absorption requires several steps:

1. Stomach acid and pepsin cleave B12 from food protein in the stomach.
2. B12 binds to haptocorrin (a salivary protein) in the stomach.
3. In the duodenum, pancreatic enzymes release B12 from haptocorrin.
4. B12 then binds to intrinsic factor (produced by gastric parietal cells).
5. The B12-intrinsic factor complex is absorbed in the terminal ileum.

PPIs powerfully suppress gastric acid. Without acid, step 1 fails — B12 cannot be cleaved from food protein efficiently. The result is reduced absorption of dietary B12, with normal absorption of supplemental crystalline B12 (which is not protein-bound).

This is a slow process. The body's liver stores of 2,000–5,000 μg take 3–5 years to deplete with reduced intake. A patient just started on omeprazole this month has nothing to worry about yet.

The risk timeline

Studies consistently show:

• Measurable serum B12 decline after 1–2 years of continuous PPI use.
• Clinically significant deficiency in some patients after 4+ years on PPI.
• Risk rises with PPI dose and duration.

The threshold for action is around 2 years of continuous PPI use — at this point, annual B12 screening is reasonable.

Who is most at risk

Risk is compounded by other factors:

• Age over 65. Older adults already have reduced gastric acid and reduced intrinsic factor production. Adding PPI amplifies a problem already present.
• Vegetarians and vegans on PPI. Low dietary B12 intake combined with reduced absorption — see vegan B12.
• Patients on metformin + PPI. Both reduce B12 absorption by different mechanisms; combined risk is substantial. See metformin and B12 deficiency.
• Post-bariatric surgery patients. Reduced gastric volume, reduced acid, often on PPI for protection. Multi-factorial risk.
• Patients with pernicious anaemia history. Already on lifelong injections, the PPI further reduces any residual oral B12 absorption.

Symptoms to watch for

The symptoms of B12 deficiency are often attributed to other things. In an older patient on PPI:

• Fatigue, often described as more profound than the usual age-related tiredness.
• Brain fog, slowed thinking, poor concentration.
• Peripheral neuropathy — tingling, numbness in feet and hands.
• Mood changes, irritability.
• Glossitis (smooth, red, sometimes painful tongue).
• Macrocytic anaemia on routine FBC.

For wider symptom context see B12 deficiency symptoms explained.

When to test

• Annually if on PPI for >2 years.
• Immediately if symptomatic.
• Before starting long-term PPI in an older adult — establish baseline.
• Annually if also on metformin (combination risk).
• Annually if vegetarian or vegan and on PPI.

Standard panel: serum B12, FBC (looking for macrocytosis). For borderline serum B12 with symptoms, methylmalonic acid (MMA) and homocysteine provide functional confirmation. See our Manchester blood test clinic.

Treatment options

Three pathways depending on severity:

• Mild decline, asymptomatic: oral cyanocobalamin 1,000 μg daily. Recheck at 3–6 months. Note that the absorption defect makes oral less effective than usual, but at high doses the small passive-diffusion pathway often suffices.
• Moderate deficiency, mild symptoms: trial of high-dose oral (1,000–2,000 μg daily) with serum B12 monitoring. If serum B12 fails to rise within 3 months, switch to injections.
• Significant deficiency or neurological symptoms: hydroxocobalamin 1 mg IM, loading and 3-monthly maintenance. The injection route bypasses the absorption defect entirely.

For comparison of injection forms see hydroxocobalamin vs cyanocobalamin. Pernicious anaemia, where the absorption defect is irreversible, requires lifelong injections — see pernicious anaemia.

The deprescribing question

This is often the most useful question of all. PPIs are commonly continued for years on the original prescription without anyone asking whether they are still needed. NICE CKS on dyspepsia explicitly recommends regular review of PPI use.

Candidates for deprescribing:

• Patients on PPI for non-erosive reflux symptoms only, who have been controlled for 6+ months.
• Patients started on PPI for gastric protection (e.g. on NSAIDs) where the NSAID has stopped.
• Patients on PPI as an initial trial for vague dyspepsia where the diagnosis was never confirmed.

Patients who should generally continue PPI:

• Barrett's oesophagus.
• Severe erosive oesophagitis.
• Zollinger-Ellison syndrome.
• Patients on ongoing NSAIDs or anticoagulants with high GI bleed risk.
• Patients with confirmed peptic ulcer disease on maintenance.

Deprescribing protocol (with GP):

1. Halve the dose for 2 weeks.
2. Halve again for 2 weeks.
3. Stop completely, switching to H2 blocker (famotidine) on-demand if needed.
4. Lifestyle measures — weight loss if relevant, raising the head of the bed, avoiding late large meals, reducing alcohol.

Rebound acid hypersecretion is common after stopping PPIs (mostly resolves in 4–8 weeks). Slow tapering reduces severity. Patients should know to expect a difficult few weeks.

H2 blocker alternatives

Famotidine is the modern preferred H2 blocker (ranitidine was withdrawn due to NDMA contamination concerns). H2 blockers reduce acid less powerfully than PPIs but have less impact on B12 absorption. For patients who genuinely need ongoing acid suppression, an H2 blocker may be a better long-term choice than a PPI.

Practical pharmacist medication review

Many patients we see are on PPIs that no longer have a clear indication. At Trafford Clinic we offer medication reviews that include:

• Review of current PPI indication and duration.
• B12 testing as appropriate.
• Liaison with the GP for deprescribing where indicated.
• Setting up monitoring for patients who continue.

Book at any of our locations — Manchester, Old Trafford, Sale, Altrincham and Chorlton. Brand vitamin B12 page covers the wider context. For blood test booking see our Manchester blood test clinic. For interpreting your results see reading blood test results.