Why am I suddenly vitamin B deficient?

January 6, 2026 •

3 min read

According to the National Institutes of Health, vitamin B12 deficiency affects roughly 6% of the general population under 60 and up to 20% over 60. If considering, "Why am I suddenly vitamin B deficient?" it is crucial to look beyond diet and into underlying medical conditions which impair absorption.

Quick Summary

A sudden vitamin B deficiency may come from malabsorption caused by medical conditions or gastric surgery, medication side effects, and autoimmune disorders like pernicious anemia. Dietary shifts can also accelerate deficiency in specific B vitamins.

Key Points

Malabsorption is a primary cause: Digestive conditions like Crohn's, celiac disease, and pernicious anemia often cause malabsorption, leading to sudden B vitamin deficiencies, especially B12.
Medications can interfere: Long-term use of certain drugs, such as proton pump inhibitors (PPIs) and the diabetes medication metformin, can impede vitamin B12 absorption.
Alcohol depletes B vitamins quickly: Excessive and chronic alcohol consumption accelerates the depletion of multiple B vitamins by hindering absorption and increasing their excretion.
Surgery is a risk factor: Gastric surgeries, including gastric bypass, can permanently alter the digestive tract and impair the absorption of key nutrients like vitamin B12.
Symptoms can mimic other conditions: The neurological and psychological symptoms of a B vitamin deficiency, such as fatigue and confusion, can often be mistaken for other ailments, delaying diagnosis.

Understanding the B Vitamins

The B vitamins are a complex of eight water-soluble vitamins vital for various bodily functions, including energy production, brain health, and red blood cell formation. Unlike fat-soluble vitamins, most B vitamins are not stored in significant amounts, meaning regular dietary intake is necessary. While B12 can be stored in the liver for years, a "sudden" deficiency is often triggered by factors that rapidly deplete reserves or hinder absorption, rather than just diet.

Medical Conditions Impairing Absorption

Issues with the body's ability to absorb B vitamins, particularly B12, are common causes of sudden deficiency, even with adequate intake.

Pernicious Anemia

Pernicious anemia is an autoimmune condition where the body attacks stomach cells that produce intrinsic factor, which is necessary for B12 absorption in the small intestine. This leads to a B12 deficiency that can manifest with sudden neurological symptoms once body stores are depleted.

Gastrointestinal Disorders

Chronic conditions affecting the digestive system can significantly impede nutrient absorption:

Inflammatory Bowel Diseases: Crohn's and Celiac disease can damage the intestinal lining where B12 is absorbed.
Gastritis: Inflammation of the stomach lining can reduce stomach acid needed to release B12 from food. This is more common in older adults.
Bacterial Overgrowth: Small intestinal bacterial overgrowth (SIBO) can result in bacteria consuming B12 before the body can absorb it.

Surgical History

Certain gastrointestinal surgeries increase the risk of B vitamin deficiencies.

Gastric Bypass or Gastrectomy: These procedures can remove or bypass areas involved in producing intrinsic factor or absorbing B12.

Medications and Substance Use

Some medications and lifestyle factors can interfere with B vitamin absorption and metabolism.

Medications that Deplete B Vitamins

Acid-Reducing Drugs: Proton pump inhibitors (PPIs) and H2 blockers decrease stomach acid, hindering B12 release from food, especially with long-term use.
Metformin: This diabetes medication can interfere with intestinal B12 absorption.
Other Medications: Some antibiotics and chemotherapy drugs can lead to B vitamin depletion. Repeated exposure to nitrous oxide can also inactivate B12.

Alcohol Use

Excessive alcohol intake significantly affects B vitamin levels by interfering with absorption and increasing excretion. It also impacts liver function where B12 is stored.

Comparison of Major B Vitamin Deficiency Causes


Cause	Primary B Vitamins Affected	Speed of Onset	Key Mechanism
Pernicious Anemia	B12	Gradual onset with sudden symptom appearance	Immune system attacks intrinsic factor-producing cells.
Gastric Surgery	B12	Potentially sudden after surgery	Physical removal of B12 absorption sites.
Gastrointestinal Disease	All B vitamins	Variable, depends on severity	Inflammation or damage to intestinal lining impairs absorption.
Medication Use (PPIs, Metformin)	B12, Folate	Gradual onset over time	Reduced stomach acid or interference with absorption pathways.
Alcohol Use Disorder	B1, B6, B9, B12	Rapid onset due to increased excretion	Impaired absorption and increased urinary excretion.
Strict Vegan Diet	B12	Gradual onset over years	Inadequate dietary intake from animal-based foods.

Addressing a Sudden Deficiency

If a sudden B vitamin deficiency is suspected, it is crucial to consult a healthcare professional for diagnosis and treatment. Blood tests can confirm levels and help identify the underlying cause. Treatment varies; B12 deficiency due to malabsorption often requires injections, while oral supplements may be used for diet-related issues. Folate deficiency is commonly treated with oral folic acid. Managing the underlying condition, adjusting medications, or making dietary changes are also key parts of treatment.

Conclusion

A sudden B vitamin deficiency, particularly of B12, is often a sign of an underlying issue affecting absorption or utilization rather than solely dietary factors. Autoimmune conditions, gastrointestinal disorders, certain medications, and heavy alcohol use can cause a rapid drop in levels. Given that symptoms can affect the nervous system and potentially cause irreversible damage if untreated, prompt medical evaluation is essential to identify the cause and initiate appropriate treatment.

*The National Institute of Diabetes and Digestive and Kidney Diseases provides further information on Crohn's disease and its effects on the digestive system and nutrient absorption.

Frequently Asked Questions

While the depletion of B vitamins like B12 can take years due to liver storage, the onset of symptoms can appear suddenly due to an underlying event, such as a new medication, surgery, or the progression of an autoimmune disorder.

The most common cause of B12 deficiency in developed countries is impaired absorption rather than diet alone. A frequent reason is pernicious anemia, an autoimmune condition that prevents the body from producing the intrinsic factor needed for absorption.

Medical conditions that can cause B vitamin deficiency include autoimmune diseases (e.g., pernicious anemia, celiac disease), inflammatory bowel diseases (e.g., Crohn's disease, ulcerative colitis), and conditions that affect stomach acid production like chronic gastritis.

Certain medications, such as proton pump inhibitors (PPIs), H2 blockers, and metformin, can interfere with the production of stomach acid or the absorption pathways needed to utilize B vitamins from food effectively over time.

Early symptoms often include fatigue, weakness, a sore or red tongue, and paresthesias (pins and needles) in the hands and feet. Symptoms can progress to include memory problems, balance issues, and psychological changes.

Yes, excessive alcohol consumption can accelerate B vitamin depletion. It impairs absorption in the digestive tract and increases the excretion of B vitamins through the kidneys, leading to a more rapid deficiency.

Treatment depends on the cause. For malabsorption, injections of vitamin B12 may be required. For dietary issues, high-dose oral supplements may be prescribed. It is crucial to consult a healthcare provider for diagnosis and to address any underlying causes.