B12 Deficiency and Burning Feet: When Your Stomach Is the Cause

B12 deficiency can cause burning, tingling and numb feet. One of the most overlooked reasons is a stomach that has quietly stopped absorbing the vitamin. If your feet burn and no one has found a cause, ask for more than one B12 level. Ask for methylmalonic acid, both stomach antibodies, iron studies and a medication review.

People with burning feet get sent to look at their spine, their blood sugar or their shoes. Almost nobody gets sent to look at their stomach. Yet the vitamin your longest nerves need cannot enter the body without a protein the stomach lining makes. That chain is the subject of Chapter 6 of The Angry Gut, the new book from Dr. Gurpreet Singh Padda, MD, MBA, MHP, and coauthor Ami Michelle Grimes (announced here).

How can a stomach problem make my feet burn?

Think of B12 as a package that needs an escort. Stomach acid frees it from food. Intrinsic factor, made by the parietal cells of the stomach lining, grabs it and carries it the full length of the small bowel to a receptor at the very end. No escort, no delivery. Only about 1% of the vitamin slips in without that help.¹

The nerves that run to your toes are the longest in the body. They sit at the far end of the longest supply line. So they are the first to fail when supply runs short. That is why a B12 problem so often starts in both feet as numbness, pins and needles or burning. Then it climbs toward the calves.

Two things destroy that lining. One is an immune attack on the parietal cells. The other is a long-running H. pylori infection. Either one causes atrophic gastritis. When the autoimmune form causes B12 deficiency, it is called pernicious anemia.

Why was I never told my stomach could be involved?

Because the name points everyone at the wrong test. “Pernicious anemia” suggests a blood-count problem. A 2025 perspective on the English national guideline notes that anemia is present in only 15% to 20% of pernicious anemia diagnoses.²

In the chapter, I walked past the four years before this diagnosis. Those were the years when the lab work kept coming back fine. That was the wrong place to stop. The stomach fails in an order, and B12 is near the end of it.

• Iron usually goes first. Sometimes the damage sits in the upper, acid-making part of the stomach. Then up to half of patients run low on iron, often well before B12 drops.³
• It is rarely one nutrient. One center tracked 122 patients diagnosed by biopsy. Of those, 76 were short on at least one of B12, iron, vitamin D or folate, and 52 were short on more than one.⁴
• The wait is long. The median delay to diagnosis in the autoimmune gastritis literature is 14 months.⁴
• The lining does not wait with you. A prospective study followed 270 patients. The stomach tissue of every one of them got worse over time, usually within three years. None got better on its own.⁴

Who is most likely to have a stomach-driven B12 problem?

The people already at risk for nerve damage carry the highest odds.

• Type 1 diabetes. The risk of autoimmune gastritis runs about three to five times that of the general public.⁴
• Thyroid disease. Autoimmune thyroiditis shows up in 36% to 44% of people with autoimmune gastritis. Turned around, about 40% of people with autoimmune thyroid disease have this kind of stomach atrophy.⁴ If you have Hashimoto’s and burning feet, both belong in the same talk. See how thyroid function affects your nerves.
• Long-term metformin. In the Diabetes Prevention Program, adults at high risk for type 2 diabetes were randomized to metformin (1,073 people) or placebo (1,082). At five years, low or borderline-low B12 (at or below 298 pg/mL) showed up in 19.1% on metformin. On placebo it was 9.5%. The extra neuropathy on metformin showed up only in the people whose B12 had fallen low.⁵ Never stop metformin on your own. Ask for the B12 workup instead. More in how statins and metformin can affect nerve health.
• Daily acid blockers. A large study compared patients with and without B12 deficiency. People taking more than 1.5 proton pump inhibitor pills a day had nearly double the odds of B12 deficiency (odds ratio 1.95).⁶
• Weight-loss surgery. A Portuguese hospital tracked 505 patients in a row. At twelve months, B12 deficiency ran 16.74% after gastric bypass. After sleeve gastrectomy it was 0.93%.⁷ See nerve damage after stomach or bowel surgery.

Follow the money and the list stops looking random. We subsidize cheap calories. The calories cause the diabetes. The diabetes earns the metformin. And the metformin drains the vitamin while one blood test keeps saying all is fine. None of that is the patient’s failure.

What should I have measured if my feet burn?

A single B12 level tells you how much vitamin is in the blood. It does not tell you whether your nerves are getting it (see why a normal B12 can miss a deficiency). Bring this fuller list to your visit.

1. Serum B12, read against the right lines. In American primary care, below 180 pg/mL is diagnostic and 180 to 350 pg/mL is borderline.⁸
2. Methylmalonic acid if you land in that borderline band. It rises when B12 fails inside the cell. Kidney problems, dehydration, low thyroid and bacterial overgrowth in the small bowel can also raise it. So it has to be read with those in mind.⁹
3. Both stomach antibodies, together. Anti-parietal cell and anti-intrinsic factor antibodies each miss cases on their own. Run as a pair, they reached 90% sensitivity and 95.7% specificity in a 2025 comparison of assays in autoimmune gastritis.¹⁰ A negative intrinsic factor antibody alone does not rule the problem out. It tends to turn positive later in the disease.³
4. Ferritin and iron studies, including the oldest ones in your chart. A low iron years ago may have been the first clue.
5. A medication history that counts years of metformin and daily dose, and years of acid blockers.
6. Gastrin only after an acid blocker is stopped. A proton pump inhibitor can raise gastrin three to five times. That makes the result useless.²

Do not wait for large red blood cells either. They are a late sign, and other problems can cause them too. Some patients low on B12 show nothing wrong on the blood count at all.⁹

Does it change treatment if my stomach is the cause?

Yes. When the absorption machinery is gone, a supplement bottle is a gamble on that 1% side door. England’s 2024 national guideline offers lifelong B12 shots when autoimmune gastritis is the cause or suspected cause, or after total gastrectomy.¹¹ In the chapter’s case, a man whose stomach had almost no parietal cells left went on shots, not tablets. Eleven months later his walking was steadier. Some of what he lost did not come back. That is the cost of finding it late.

A burning foot is a symptom. The cause may be hiding in the stomach, the medication list or the iron history. You can ask about all of them this week. You do not have to accept “idiopathic” while those questions are still open. The chapter’s free technical supplement is at theangrygut.com/chapter-6.

Questions patients ask about B12 and burning feet

Can low B12 cause burning feet even if I am not anemic?

Yes. Anemia shows up in only a minority of pernicious anemia diagnoses. So a normal blood count does not rule out a B12 problem reaching the nerves. See what causes burning, numb or painful feet.

I have diabetes. How do I know if it is B12 and not my blood sugar?

You often cannot tell from symptoms alone, and both can be present. Metformin use, type 1 diabetes and thyroid disease all raise the odds of a B12 problem. That is why a diabetic patient with burning feet deserves B12 testing too. See diabetic peripheral neuropathy treatment in St. Louis.

Should I just start taking a B12 supplement?

Get tested first. If the stomach can no longer absorb the vitamin, a tablet depends on that 1% side door. England’s national guideline recommends shots instead when autoimmune gastritis is the cause. The form and dose are a medical decision. See nutritional deficiencies beyond B12.

Sources

1. Chan CQH, Low LL, Lee KH. Oral vitamin B12 replacement for the treatment of pernicious anemia. Frontiers in Medicine. 2016;3:38. doi.org
2. Thain A, Hart K, Ahmadi KR. Addressing the gaps in the vitamin B12 deficiency 2024 NICE guidelines: highlighting the need for better recognition, diagnosis, and management of pernicious anaemia. European Journal of Clinical Nutrition. 2025;79(7):607–610. doi.org
3. Shah SC, Piazuelo MB, Kuipers EJ, Li D. AGA clinical practice update on the diagnosis and management of atrophic gastritis: expert review. Gastroenterology. 2021;161(4):1325–1332. doi.org
4. Rustgi SD, Bijlani P, Shah SC. Autoimmune gastritis, with or without pernicious anemia: epidemiology, risk factors, and clinical management. Therapeutic Advances in Gastroenterology. 2021;14:17562848211038771. doi.org
5. Aroda VR, Edelstein SL, Goldberg RB, et al. Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. Journal of Clinical Endocrinology and Metabolism. 2016;101(4):1754–1761. doi.org
6. Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435–2442. doi.org
7. Vieira de Sousa JP, Santos-Sousa H, Vieira S, et al. Assessing nutritional deficiencies in bariatric surgery patients: a comparative study of Roux-en-Y gastric bypass versus sleeve gastrectomy. Journal of Personalized Medicine. 2024;14(6):650. doi.org
8. Patel H, McGuirk R. Vitamin B12 deficiency: common questions and answers. American Family Physician. 2025;112(3):294–300. pubmed.ncbi.nlm.nih.gov
9. Harrington DJ, Stevenson E, Sobczyńska-Malefora A. The application and interpretation of laboratory biomarkers for the evaluation of vitamin B12 status. Annals of Clinical Biochemistry. 2024;62(1):22–33. doi.org
10. Osmola M, Hémont C, Romańczyk M, et al. A comparative study of different assays for autoantibodies detection in patients with autoimmune gastritis. Journal of Translational Autoimmunity. 2025;10:100294. doi.org
11. National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239). 2024. nice.org.uk