Can Fatty Liver Cause B12 Deficiency?

Fatty liver disease and vitamin B12 deficiency are two conditions that frequently intersect, raising the question: can fatty liver cause B12 deficiency? The relationship is more complex than a simple cause and effect. Rather than directly depleting B12, fatty liver disease disrupts how the liver stores, processes and releases the vitamin, and both conditions share overlapping risk factors. Paradoxically, liver damage can cause serum B12 levels to appear elevated even when functional stores are low. Understanding this nuanced relationship is essential for accurate diagnosis and appropriate management.

Can fatty liver disease affect your vitamin B12 levels?

Fatty liver disease does not directly cause B12 deficiency but disrupts B12 metabolism; liver damage can paradoxically raise serum B12 by releasing stored vitamin into the bloodstream, masking true functional status.

Fatty liver disease does not directly cause vitamin B12 deficiency, but the two conditions frequently occur together because they share common underlying risk factors and metabolic pathways. Research has shown that people with metabolic dysfunction-associated steatotic liver disease (MASLD), the current umbrella term that has replaced non-alcoholic fatty liver disease (NAFLD), often have altered B12 metabolism, though the relationship is complex and not yet fully understood.^[1][2] The progressive inflammatory form of MASLD is known as metabolic dysfunction-associated steatohepatitis (MASH), which was previously called non-alcoholic steatohepatitis (NASH).^[1][2]

Interestingly, some studies have found that people with fatty liver disease may actually have elevated serum B12 levels rather than deficient ones. This can occur because a damaged or inflamed liver releases stored B12 into the bloodstream, giving a falsely reassuring or even raised reading on a blood test.^[5][6] In this context, a high B12 level may itself be a marker of liver dysfunction rather than a sign of good nutritional status.

Conversely, when fatty liver disease progresses to more advanced liver damage, such as cirrhosis, the liver's capacity to store and process B12 can become genuinely impaired, potentially contributing to deficiency over time. Alcohol-related liver disease, which is a distinct cause of fatty liver, carries a particularly strong association with B12 deficiency due to poor dietary intake, impaired absorption and disrupted storage.

Because the relationship between fatty liver and B12 is bidirectional and nuanced, it is important not to interpret B12 blood results in isolation. Anyone with known liver disease who is concerned about their B12 status should speak to their GP, who can arrange appropriate testing and interpret results in the context of overall liver health.

How the liver stores and processes vitamin B12

The liver stores the majority of the body's B12 as adenosylcobalamin and methylcobalamin; in fatty liver disease, damaged hepatocytes can leak stored B12, causing misleadingly elevated serum levels despite depleted cellular stores.

The liver is the primary storage organ for vitamin B12 in the body, holding the majority of the body's total B12 reserves, which can sustain normal function for several years even without dietary intake. This makes the liver's health directly relevant to long-term B12 status.

After B12 is absorbed in the small intestine, bound to a protein called intrinsic factor produced by the stomach, it travels via the portal circulation to the liver.^[7][17] Here it is stored as adenosylcobalamin and methylcobalamin, the two active forms of the vitamin. The liver also plays a role in the enterohepatic circulation of B12, releasing it into bile and reabsorbing it in the gut, a recycling process that helps conserve the body's stores.^[6]

In fatty liver disease, hepatocyte (liver cell) function can be disrupted. Fat accumulation within liver cells, inflammation (steatohepatitis) and eventual fibrosis can impair the liver's ability to take up, store and release B12 appropriately. Damaged hepatocytes may leak stored B12 into the circulation, and reduced clearance of B12-binding proteins may also contribute, which is why serum B12 can appear elevated in active liver disease even when cellular stores are being depleted.

B12 is carried in the blood by two main transport proteins: transcobalamin, which is produced by several tissues including vascular endothelium and the liver, and haptocorrin, which is derived primarily from salivary glands and granulocytes rather than the liver.^[6] Liver disease can affect the levels and function of these proteins, potentially altering how B12 is delivered to tissues throughout the body. This means that even when a blood test shows an apparently normal or high B12 level, the amount of B12 that is biologically active and available to cells may be lower than the figure suggests. Measurement of holotranscobalamin (active B12) or methylmalonic acid can provide a more accurate assessment of functional B12 status in this context.^[22][23]

Which conditions linked to fatty liver also lower B12?

Long-term metformin use, bariatric surgery, alcohol-related liver disease, malabsorptive gut conditions and pernicious anaemia are key co-existing causes of B12 deficiency in people with fatty liver disease.

Several conditions that commonly occur alongside fatty liver disease can independently reduce B12 levels, making it difficult to attribute deficiency to liver disease alone. Understanding these overlapping risk factors is important for accurate diagnosis and management.

Type 2 diabetes is strongly associated with MASLD. People with type 2 diabetes who take metformin, one of the most widely prescribed medications for the condition, are at increased risk of B12 deficiency. Metformin impairs B12 absorption in the gut. NICE guidance (NG28) and an MHRA Drug Safety Update advise that clinicians should consider periodic monitoring of B12 levels in people taking metformin long-term, particularly those with risk factors such as poor diet, and should test if symptoms of anaemia or neuropathy develop.

Obesity is a major driver of fatty liver disease and is also associated with dietary patterns that may be low in B12-rich foods such as meat, fish, eggs and dairy. Bariatric surgery, which is sometimes used to treat severe obesity and can improve fatty liver, carries a significant risk of B12 deficiency due to reduced stomach acid production and altered gut anatomy.^[12][13] The need for B12 supplementation after bariatric surgery, and the appropriate route and dose, depends on the type of procedure performed; guidance from the British Obesity and Metabolic Surgery Society (BOMSS) should be followed, and patients should discuss their individual requirements with their surgical or dietetic team.

Alcohol-related liver disease is a distinct but important cause of fatty liver. Alcohol impairs B12 absorption, reduces dietary intake and disrupts hepatic storage, making deficiency common in this group.

Coeliac disease and inflammatory bowel disease (particularly Crohn's disease affecting the terminal ileum) can co-exist with liver abnormalities and directly impair B12 absorption in the small intestine.^[15][16]

Autoimmune thyroid disease is associated with pernicious anaemia, an autoimmune condition that destroys the stomach cells producing intrinsic factor and is a common cause of B12 deficiency.^[18][19] This autoimmune link, rather than a direct metabolic effect of thyroid hormone, is the most established connection between thyroid conditions and B12 status.

Key conditions to consider include:

• Long-term metformin use

• Post-bariatric surgery (procedure-dependent)

• Alcohol-related liver disease

• Malabsorptive gut conditions

• Autoimmune thyroid disease and pernicious anaemia

A thorough clinical assessment is needed to identify which of these factors may be contributing in any individual.

How is B12 deficiency diagnosed and treated in the UK?

B12 deficiency is diagnosed via serum B12 testing through NHS GP services, with additional tests such as holotranscobalamin used in liver disease; treatment is either oral supplementation or intramuscular hydroxocobalamin injections depending on the underlying cause.

B12 deficiency is diagnosed in the UK primarily through a serum vitamin B12 blood test, which is available through NHS GP services. However, as noted above, serum B12 levels can be misleading in people with liver disease, and additional tests such as serum methylmalonic acid or holotranscobalamin (active B12) may be requested to give a clearer picture of functional B12 status. A full blood count may also reveal macrocytic anaemia, a common consequence of deficiency.

NICE and NHS guidance recommends that treatment is tailored to the underlying cause. Where deficiency is due to dietary insufficiency, oral B12 supplementation is often effective. Where it results from impaired absorption, for example due to pernicious anaemia, post-surgical changes or certain medications, intramuscular hydroxocobalamin injections are the standard NHS treatment. These are typically given as a loading course followed by maintenance injections every two to three months. Where neurological symptoms are present, an intensified injection schedule may be used; new or rapidly progressive neurological symptoms should prompt urgent same-day clinical assessment.

For people taking metformin, clinicians should consider periodic monitoring of B12 levels, particularly in those with risk factors, and supplementation should be offered if deficiency is confirmed. People who have undergone bariatric surgery should discuss their B12 supplementation requirements with their surgical or dietetic team, as the appropriate regimen depends on the procedure performed.

If you have fatty liver disease and are experiencing symptoms that may suggest B12 deficiency, such as persistent fatigue, tingling or numbness in the hands or feet, difficulty concentrating or mouth soreness, you should contact your GP for assessment. These symptoms can have many causes, and a blood test is the appropriate first step. If symptoms are severe or rapidly worsening, contact NHS 111 for timely advice. Do not attempt to self-diagnose or self-treat without professional guidance, particularly if you have known liver disease, as interpreting B12 results in this context requires clinical expertise.

If you believe a medicine you are taking may have caused or worsened a B12 deficiency, you can report this as a suspected side effect to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Scientific References

1. A multisociety Delphi consensus statement on new fatty liver disease nomenclature.
2. Understanding the evolving nomenclature of steatotic liver disease.
3. EASL position paper on preclinical models of steatotic liver disease.
4. Current Update on Nomenclature, Diagnosis, and Management of Metabolic Dysfunction-associated Steatotic Liver Disease: Radiologists' Perspective.
5. Vitamin B12 and homocysteine levels in patients with NAFLD: a systematic review and metanalysis.
6. Pathophysiology of hypervitaminosis B12: from origin to clinical event. Scoping review.
7. Vitamin B12 or folate deficiency anaemia – Causes.
8. Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk.
9. Type 2 diabetes in adults: management (NG28) – Medicines safety.
10. Proton Pump Inhibitors, H2-Receptor Antagonists, Metformin, and Vitamin B-12 Deficiency: Clinical Implications.
11. Vitamin B12 and bariatric surgery – advice during COVID-19.
12. The Nutritional Challenges Following Revisional Bariatric Surgery After Sleeve Gastrectomy: A Systematic Review and Meta-Analysis.
13. Prevalence and correlates of anemia following Roux-en-Y gastric bypass: a systematic review and meta-analysis.
14. Comparative risk of anemia and related micronutrient deficiencies after Roux-en-Y gastric bypass and sleeve gastrectomy: an updated meta-analysis of randomised controlled trials.
15. Prevalence and Risk Factors for Functional Vitamin B12 Deficiency in patients with Crohn's disease.
16. Vitamin B12 malabsorption in patients with limited ileal resection.
17. Intrinsic factor secretion and cobalamin absorption. Physiology and pathophysiology in the gastrointestinal tract.
18. Autoimmune mechanisms in pernicious anaemia & thyroid disease.
19. Clinical and Subclinical Thyroid Disorders Associated with Pernicious Anemia.
20. Hydroxocobalamin – BNF.
21. Having your hydroxocobalamin injection.
22. An audit of holotranscobalamin ("Active" B12) and methylmalonic acid as markers of vitamin B12 status.
23. Active B12 assay for diagnosing vitamin B12 deficiency (MIB40).

Frequently Asked Questions