Vitamin B12 and Diabetes: What You Need to Know

Explore the critical connection between vitamin B12, diabetes management, and the role of medications like metformin in B12 deficiency.

By Medha deb

Created on Sep 26, 2025

Explore the critical connection between vitamin B12, diabetes management, and the role of medications like metformin in B12 deficiency.

For individuals managing diabetes, paying attention to overall nutrition is key — and one essential nutrient to monitor closely is vitamin B12. This vitamin is crucial for energy production, nerve function, and DNA synthesis. However, people with diabetes, especially those taking medications like metformin, have a higher risk of developing vitamin B12 deficiency. This guide explores why B12 matters, how diabetes and its treatments influence B12 status, deficiency symptoms, testing, and strategies to maintain optimal levels.

Understanding Vitamin B12

Vitamin B12, or cobalamin, is a water-soluble nutrient naturally present in animal-sourced foods. It is vital for:

Red blood cell formation
Nerve function
DNA synthesis and cell division
Supporting brain health

The body does not produce vitamin B12; you must obtain it through diet or supplements. The vitamin is stored mainly in the liver, and the body’s reserves can last for years, but certain conditions can lead to faster depletion.

Vitamin B12 and Diabetes — The Key Connection

Research consistently shows that people with type 1 and, more often, type 2 diabetes are at an increased risk for vitamin B12 deficiency, especially those treated with metformin, a common first-line medication for type 2 diabetes management. Several large studies estimate B12 deficiency rates in type 2 diabetes patients taking metformin range from 5.8% to 33%.

The increased risk can be attributed to:

Effects of diabetes on gut absorption
Long-term or high-dose metformin use, which impairs B12 absorption
Restricted diets (e.g., vegan or vegetarian)

How Metformin Affects Vitamin B12

Metformin is widely prescribed for type 2 diabetes due to its proven efficacy and safety profile. However, it is also well documented that metformin can lead to decreased absorption of vitamin B12 from the digestive tract. This effect can begin as early as a few months after starting the medication and becomes more significant with higher doses and longer duration of therapy.

Metformin may reduce B12 levels through:

Interference with vitamin B12’s absorption in the small intestine
Changes in small bowel motility, increasing bacterial overgrowth that uses B12
Altering levels of intrinsic factor—a protein vital for B12 uptake
Impairment of calcium-dependent absorption, which can sometimes be mitigated by calcium supplementation

Despite the benefits in glycemic control, studies show a steady decline in B12 levels over years of metformin use. Symptoms of deficiency may not present for 5–10 years due to the body’s liver stores.

Other Risk Factors for B12 Deficiency in Diabetes

Beyond metformin use, several other factors increase the risk of vitamin B12 deficiency among people with diabetes:

Age over 50
Strict vegetarian or vegan diets (no animal products)
Gastric surgery (such as bariatric surgery)
Digestive disorders (celiac, Crohn’s, chronic gastritis)
Long-term use of acid-reducing drugs (proton pump inhibitors, H2 blockers)

Why Vitamin B12 Is Important for People with Diabetes

For those with diabetes, maintaining healthy B12 levels is essential for several reasons:

Nerve Health: B12 is critical for nerve protection and repair. Deficiency can worsen or mimic diabetic neuropathy—nerve damage that is a serious complication of diabetes.
Red Blood Cell Production: Low B12 causes megaloblastic anemia, resulting in fatigue and weakness. These symptoms may be mistakenly attributed to diabetes itself.
Heart Health: B12 helps lower homocysteine, a compound tied to higher cardiovascular risk.
Mental Health: B12 deficiency is linked to cognitive impairment, mood changes, and memory loss, which can further challenge diabetes management.

Symptoms of Vitamin B12 Deficiency

The signs of B12 deficiency can be subtle at first, or may overlap with symptoms of diabetes or aging. Common symptoms include:

Numbness or tingling (especially in the hands and feet)
Muscle weakness and lack of coordination
Fatigue and reduced energy
Pale or jaundiced skin
Shortness of breath or heart palpitations
Mood changes, memory loss, or confusion
Glossitis (sore, red, or swollen tongue) and mouth ulcers
Blurred vision

Untreated, severe B12 deficiency can cause lasting nerve damage and neurological complications.

Testing for Vitamin B12 Deficiency

If you have diabetes, especially if you take metformin or have symptoms of deficiency, routine screening for B12 status is advised:

Blood tests for serum B12 levels. However, these do not always detect early or mild deficiencies due to storage in tissues.
Additional markers like methylmalonic acid (MMA) and homocysteine are more sensitive to early deficits.
- High MMA (over 250 nmol/L) can indicate cellular deficiency even if B12 serum level appears normal.
Your healthcare provider may also look for megaloblastic anemia in a complete blood count (CBC).

Test	What it Measures	What Low Level Means
Serum B12	B12 in blood	Possible deficiency
Methylmalonic Acid (MMA)	B12 activity in cells	Elevated in deficiency
Homocysteine	Related marker	Elevated in deficiency
Complete Blood Count (CBC)	Red blood cell appearance	May show anemia

Recommended Vitamin B12 Intake

The recommended daily allowance (RDA) for vitamin B12 in adults is 2.4 micrograms (mcg), but higher doses may be necessary for those with absorption issues or certain medical conditions.

Pregnant women: 2.6 mcg daily
Breastfeeding women: 2.8 mcg daily

Some individuals with diabetes or on metformin may require supplements far exceeding these baselines to maintain blood levels.

Best Dietary Sources of Vitamin B12

Vitamin B12 is naturally found in animal-based products. Rich dietary sources include:

Beef liver and organ meats
Fish (salmon, trout, tuna, sardines)
Shellfish (clams, oysters)
Poultry
Eggs
Dairy products (milk, yogurt, cheese)

For those on vegan or vegetarian diets, fortified foods (like plant-based milks, cereals, and nutritional yeast) and B12 supplements are critical.

Vitamin B12 Supplements: Types and Dosages

Supplements are available in several forms:

Cyanocobalamin (most common; synthetic form)
Methylcobalamin (active form found in the body; sometimes preferred for nerve health)
Hydroxocobalamin and adenosylcobalamin (used in some countries or special cases)

B12 supplements can be taken as:

Oral tablets
Sublingual (under the tongue) lozenges
Injections (for people with significant absorption problems or severe deficiencies)

Your healthcare provider will recommend the best form and dose based on your individual health and risk profile.

Managing and Preventing B12 Deficiency in Diabetes

Regular screening for B12 levels is recommended for people with diabetes using metformin, especially after several years of therapy.
Discuss any symptoms such as unexplained fatigue, nerve discomfort, or cognitive changes with your healthcare team.
If you are at risk or already deficient, supplement as prescribed—this can quickly restore normal levels and prevent complications.
If you follow a vegetarian or vegan diet, plan for fortified foods or routine supplementation.
If you use metformin and are found to be deficient, you may need periodic high-dose oral B12 or injections.
Monitor for any ongoing nerve-related symptoms, as they may not resolve even after B12 correction if deficiency lasted a long time.

Frequently Asked Questions (FAQs)

Q: Who is most at risk for vitamin B12 deficiency with diabetes?

A: People with type 2 diabetes, particularly those taking metformin for several years, adults over age 50, and anyone with digestive disorders or restricted diets are most at risk.

Q: How often should B12 levels be checked if I take metformin?

A: Most guidelines suggest checking vitamin B12 levels at baseline and then every 1–2 years while taking metformin, or sooner if symptoms develop.

Q: What is the best way to increase B12 if I’m deficient?

A: Your provider may recommend oral B12 supplements or, in cases of significant deficiency or malabsorption, B12 injections. In most people, supplementation is effective and safe.

Q: Can taking more B12 cause side effects?

A: Vitamin B12 is generally safe, and excess amounts are excreted in urine. However, taking extremely high doses long-term should be done under medical supervision.

Q: Does B12 supplementation improve diabetes itself?

A: While B12 supplementation does not directly lower blood sugar, it is important for preventing or treating nerve-related complications. Some clinical trials suggest that correcting B12 deficiency may help improve nerve health and quality of life in diabetes, but it is not a cure for diabetes itself.

Takeaway Message

Vitamin B12 plays a vital role in the health of people with diabetes. If you take metformin or have other risk factors, work with your healthcare team to ensure you get proper screening, understand deficiency symptoms, and take supplements when needed. Prompt detection and treatment protects nerve health, energy, cognition, and overall well-being.

References

Author

medha deb

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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