Why is vitamin B12 getting low?

According to an analysis of NHANES data from 2007–2018, approximately 3.6% of adults aged 19 and older have vitamin B12 deficiency. Addressing the question of why is vitamin B12 getting low involves looking at both dietary intake and the body's complex ability to absorb this vital nutrient.

Quick Summary

Vitamin B12 levels can drop due to dietary restrictions, malabsorption issues from conditions like gastritis or Crohn's disease, certain medications, and age-related factors.

Key Points

• Malabsorption is a top cause: The body's inability to properly absorb B12 is a more frequent cause of deficiency than low intake, often due to conditions like pernicious anemia or low stomach acid.

• Age increases risk: As people get older, their stomach acid production naturally decreases, making it harder to absorb B12 from food.

• Diet matters, especially for vegans: B12 is primarily found in animal products, so those on a strict vegan or vegetarian diet are at a higher risk unless they supplement or consume fortified foods.

• Medications can interfere: Certain drugs, including metformin for diabetes and proton pump inhibitors for acid reflux, can lower B12 absorption.

• Symptoms range from fatigue to nerve damage: Early signs include tiredness and weakness, but a chronic deficiency can lead to severe and potentially irreversible neurological problems.

• Treatment varies by cause: Depending on the root issue, treatment can involve high-dose oral supplements or regular B12 injections.

What is Vitamin B12 and Why It's Crucial?

Vitamin B12, also known as cobalamin, is an essential water-soluble vitamin that the body cannot produce on its own. It is critical for numerous bodily functions, including the formation of red blood cells, neurological function, and DNA synthesis. The human body can store a large amount of vitamin B12, primarily in the liver, meaning a deficiency can take several years to develop after dietary intake ceases. A deficit can lead to a wide range of issues, from fatigue and neurological damage to megaloblastic anemia. The reasons for this deficiency are varied, often stemming from poor absorption rather than just inadequate consumption.

Malabsorption is a Major Culprit

For most people, the most common reason for low B12 levels is not insufficient intake but rather an inability to absorb the vitamin correctly. The process of B12 absorption is a complex journey through the digestive system, and it can be disrupted at several points.

Stomach-Related Issues

• Pernicious Anemia: This is an autoimmune condition where the body's immune system attacks and destroys the parietal cells in the stomach lining. These cells produce intrinsic factor, a protein essential for B12 absorption in the small intestine. Without intrinsic factor, B12 cannot be properly absorbed, leading to a severe and persistent deficiency.
• Decreased Stomach Acid (Achlorhydria): As people age, stomach acid production often decreases. Stomach acid is needed to separate B12 from the food proteins it's bound to. While this doesn't affect B12 from supplements, it significantly hinders the body's ability to absorb it from food sources, making older adults a high-risk group.
• Gastritis: Inflammation of the stomach lining can lead to decreased hydrochloric acid and intrinsic factor production, impeding B12 absorption. A common cause of gastritis is infection with Helicobacter pylori bacteria, which has been linked to B12 malabsorption.

Intestinal Disorders

• Digestive Diseases: Conditions like Crohn's disease and celiac disease can cause inflammation and damage to the intestines, especially the terminal ileum where B12 is absorbed. This damage directly impairs the body's ability to absorb the vitamin.
• Small Intestine Bacterial Overgrowth (SIBO): An overgrowth of bacteria in the small intestine can cause the bacteria to consume the B12 before the body has a chance to absorb it.
• Bariatric Surgery: Surgical procedures that remove or bypass parts of the stomach or small intestine, such as a gastric bypass, drastically reduce the production of intrinsic factor and the surface area for absorption. As a result, patients often require lifelong B12 supplementation, usually via injections.

Dietary Habits and Medications

Beyond absorption issues, what you eat and the medications you take can also impact your B12 levels.

Dietary Restrictions

• Vegan and Vegetarian Diets: Vitamin B12 is found almost exclusively in animal products like meat, fish, eggs, and dairy. Strict vegetarians and vegans who do not consume fortified foods or supplements are at a high risk of developing a B12 deficiency.
• Alcohol Misuse: Chronic, excessive alcohol consumption can damage the digestive system, making it harder for the body to absorb nutrients, including B12.

Medications

Several prescription drugs are known to interfere with B12 absorption:

• Metformin: This medication, used to treat type 2 diabetes, is known to reduce serum B12 concentrations. The risk increases with higher doses and longer use.
• Proton Pump Inhibitors (PPIs): Drugs like omeprazole and lansoprazole, which reduce stomach acid to treat acid reflux, can lead to B12 malabsorption over time because acid is needed to release B12 from food.
• H2 Blockers: Similar to PPIs, these medications (e.g., cimetidine, ranitidine) reduce stomach acid and can affect B12 levels.

Comparison of B12 Deficiency Causes

Cause Category	Mechanism of Deficiency	Risk Factors	Treatment Approach
Malabsorption	Inability to absorb B12 due to internal issues like lack of intrinsic factor, low stomach acid, or gut damage.	Older age, pernicious anemia, bariatric surgery, Crohn's/Celiac disease, H. pylori infection.	Injections (hydroxocobalamin or cyanocobalamin) or high-dose oral supplements (bypass initial absorption steps).
Dietary	Insufficient intake of B12 from food sources.	Vegan or strict vegetarian diet, chronic alcohol misuse.	Fortified foods, oral supplements, or adjusting diet to include animal products.
Medication-Induced	Interference with B12 absorption or metabolism by certain drugs.	Use of metformin, PPIs, H2 blockers.	Monitoring B12 levels, adjusting medication dosage if possible, or taking B12 supplements.

Recognizing the Symptoms and Diagnosis

The symptoms of low B12 can be subtle and develop gradually, often starting with general feelings of weakness and fatigue. As the deficiency progresses, more severe symptoms can emerge.

The Common Signs of Low B12

• Physical: Persistent fatigue, weakness, pale or yellowed skin, a sore or swollen tongue (glossitis), and weight loss.
• Neurological: Numbness or tingling sensations (pins and needles) in the hands and feet, difficulty with balance or walking, memory loss, and poor concentration. Severe, prolonged deficiency can lead to irreversible nerve damage.
• Psychological: Mood changes, such as irritability, anxiety, and depression, can occur. In extreme cases, a deficiency can contribute to paranoia or dementia.

To diagnose a B12 deficiency, a healthcare provider will typically order blood tests to measure the vitamin's levels. Further tests, such as checking methylmalonic acid (MMA) or homocysteine levels, may be needed for a more complete picture, especially when absorption issues are suspected.

Boosting Your Vitamin B12 Levels

Treatment depends on the underlying cause of the deficiency. For many, simply increasing intake through diet or oral supplements is enough, but those with absorption problems may require a more direct approach.

Treatment Options

• Supplements: For those with dietary deficiencies or mild malabsorption, high-dose oral B12 supplements can be effective. The body can absorb a small percentage of B12 from supplements without intrinsic factor, so high doses can compensate. Sublingual forms are also available and work similarly.
• Injections: For severe deficiencies or absorption issues like pernicious anemia, regular B12 injections are the standard treatment. This method bypasses the digestive system entirely, ensuring the vitamin reaches the bloodstream directly. Injections may be needed for life, depending on the cause.
• Fortified Foods: Vegans and vegetarians can prevent deficiency by regularly consuming foods fortified with B12, such as cereals, nutritional yeast, and plant-based milks.
• Food Sources: Most people can maintain adequate levels by consuming B12-rich animal products, including meat (especially beef liver and ground beef), fish (salmon, tuna), eggs, and dairy.

Management Strategies

If you have a diagnosed deficiency, your doctor will determine the best course of action. Following a personalized treatment plan is essential to prevent long-term complications. For those at risk, regular screening is a proactive way to catch a drop in B12 levels early before symptoms manifest.

Conclusion

Vitamin B12 deficiency is a surprisingly common condition with a range of potential causes, from dietary choices to complex digestive disorders and medication side effects. While inadequate consumption can be a factor, poor absorption is the more frequent culprit, especially among older adults and those with specific health conditions. Recognizing the subtle symptoms is key to early diagnosis, as left untreated, low B12 can lead to serious and sometimes irreversible neurological damage. Fortunately, effective treatments are available, including oral supplements and injections, that can restore levels and prevent complications. If you suspect your B12 levels may be low, consulting a healthcare provider is the most important step toward getting a correct diagnosis and a personalized treatment plan.

For more detailed information on vitamin B12, including dietary reference intakes and sources, you can visit the NIH Office of Dietary Supplements website.

Frequently Asked Questions

Can diet alone cause vitamin B12 deficiency?

Yes, diet can cause a B12 deficiency, especially for strict vegans or vegetarians who do not consume fortified foods or supplements. This is because vitamin B12 is found almost exclusively in animal products.

What is pernicious anemia and how does it cause low B12?

Pernicious anemia is an autoimmune condition where the body attacks and destroys the stomach cells that produce intrinsic factor. Intrinsic factor is a protein essential for B12 absorption, and its absence leads to deficiency regardless of dietary intake.

How does aging lead to low vitamin B12?

Older adults often produce less stomach acid, which is needed to separate B12 from food proteins for absorption. This age-related decrease in absorption makes them a high-risk group for B12 deficiency.

Which medications can lower vitamin B12 levels?

Common medications that can reduce B12 absorption include metformin (for type 2 diabetes), proton pump inhibitors (PPIs) for acid reflux, and histamine H2 antagonists.

What are the first signs of a B12 deficiency?

The initial symptoms are often mild and general, including persistent fatigue, weakness, and a general lack of energy. Neurological symptoms like tingling may follow as the deficiency worsens.

Are oral B12 supplements effective for someone with an absorption problem?

Yes, high-dose oral B12 supplements can be effective even with absorption issues because the body can absorb a small fraction of the vitamin through a different pathway that doesn't require intrinsic factor.

Can low B12 cause nerve damage?

Yes, prolonged and severe vitamin B12 deficiency can lead to nerve damage, which may result in tingling, numbness, or difficulty walking. This damage can become permanent if left untreated for too long.