Does vitamin B12 affect your sugar?

October 7, 2025 •

3 min read

Studies indicate that up to 30% of individuals with type 2 diabetes taking the medication metformin may experience reduced vitamin B12 levels. For many, this raises a critical question: does vitamin B12 affect your sugar? The connection is more complex and indirect than many people realize.

Quick Summary

The relationship between vitamin B12 and blood sugar is complex and mostly indirect. While B12 does not directly alter glucose levels, a deficiency can disrupt metabolic processes, potentially worsening diabetic complications like neuropathy. Certain diabetes medications, especially metformin, are a primary cause of reduced B12 absorption, making monitoring crucial.

Key Points

No Direct Impact: Vitamin B12 does not directly cause an increase or decrease in blood glucose levels.
Metformin's Effect: Long-term use of metformin, a common diabetes drug, can interfere with B12 absorption, leading to deficiency.
Increased Neuropathy Risk: Vitamin B12 deficiency can worsen or mimic diabetic neuropathy symptoms like numbness and tingling, affecting nerve health.
Metabolic Disruption: Deficiency disrupts metabolic pathways involved in glucose handling and energy production, potentially contributing to glucose intolerance.
Supplements Can Help: For individuals with confirmed deficiency, correcting it may improve nerve symptoms and support overall metabolic health.
Monitoring is Key: Regular B12 level monitoring is crucial for those with diabetes, particularly patients taking metformin for an extended period.
Dietary Considerations: Individuals following vegetarian or vegan diets are at a higher risk of B12 deficiency and may require fortified foods or supplementation.

The Indirect Connection Between B12 and Blood Sugar

Vitamin B12 does not directly change blood glucose levels. However, a deficiency can significantly impact how your body handles glucose and affect overall diabetic health. The connection is indirect and relates to how a B12 deficiency impacts nerve function and energy metabolism. Metformin, a common diabetes medication, is known to interfere with B12 absorption, which is a major concern for many individuals.

Metformin and Vitamin B12 Absorption

Metformin use, particularly long-term, is a primary cause of B12 deficiency in people with type 2 diabetes. The medication affects the absorption of vitamin B12 in the small intestine. This effect increases with higher doses and longer treatment. Importantly, neurological symptoms from B12 deficiency can be similar to diabetic neuropathy, complicating diagnosis.

B12 Deficiency and Impaired Glucose Metabolism

A lack of vitamin B12 can also impact glucose metabolism. Some research suggests that B12 deficiency may lead to glucose intolerance. B12 is crucial for enzymes involved in energy production, and a deficiency can disrupt these processes, affecting glucose handling. Furthermore, B12 is important for metabolizing homocysteine. High homocysteine levels, linked to B12 deficiency, can harm blood vessels and are associated with insulin resistance and poor glucose control. For more details on B12's functions, see {Link: National Institutes of Health https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/}.

Exacerbating Diabetic Neuropathy

Diabetic neuropathy is nerve damage caused by high blood sugar. B12 deficiency also causes neuropathy with similar symptoms like tingling and numbness. This overlap can make it hard to tell the difference. Treating a B12 deficiency is important as it can reverse these nerve symptoms. Studies show B12 supplements can improve neuropathy symptoms, highlighting the need for monitoring in this group.

Dietary Sources and Supplementation

Adequate B12 is often obtained through diet for those who eat animal products. However, vegetarians, vegans, and those on long-term metformin may need supplements. Monitoring B12 levels helps determine if diet is sufficient.

Rich Dietary Sources of Vitamin B12

Meat and Poultry: Beef, chicken, and turkey.
Fish and Seafood: Clams, salmon, and tuna.
Dairy Products: Milk, cheese, and yogurt.
Eggs: Egg yolks.
Fortified Foods: Cereals, plant-based milks, and nutritional yeast.

Comparison: Healthy B12 Status vs. Deficient Status in Diabetics


Feature	Healthy B12 Status	Deficient B12 Status
Glucose Control	Supports energy production and stable glucose regulation indirectly.	Disrupts glucose metabolism, potentially worsening insulin resistance.
Nerve Health	Supports healthy nerve function.	Worsens neuropathy symptoms.
Energy Levels	Supports energy production.	Leads to fatigue and weakness.
Homocysteine Levels	Helps regulate homocysteine levels, protecting against heart issues.	High homocysteine levels, increasing cardiovascular risk.

Conclusion

The question of "does vitamin B12 affect your sugar" reveals an indirect link. While it doesn't directly change blood glucose, B12 deficiency can disrupt metabolism and worsen diabetic complications like neuropathy. This is especially true for those with type 2 diabetes taking metformin long-term. Regularly checking vitamin B12 levels is an important part of diabetes care, particularly for metformin users. Ensuring sufficient B12 through diet or supplements can help reduce deficiency risks, improve nerve health, and support overall metabolic health.

Frequently Asked Questions

No, B12 supplements do not directly lower blood sugar levels. However, for those with a deficiency, correcting it can improve overall metabolic health and potentially help stabilize glucose regulation indirectly.

Symptoms of a B12 deficiency can include fatigue, weakness, numbness or tingling in the hands and feet, memory problems, balance issues, and a sore tongue.

Metformin can interfere with the absorption of vitamin B12 in the digestive system, a side effect linked to higher dosages and longer treatment durations.

Vitamin B12 is vital for healthy nerve function. A deficiency can exacerbate or mimic diabetic neuropathy, worsening symptoms like pain and tingling sensations in the extremities.

The American Diabetes Association and other guidelines suggest periodic monitoring of vitamin B12 levels, particularly for those on high doses or long-term therapy, or if symptoms appear.

For most, a balanced diet including animal products like meat, fish, and dairy provides sufficient B12. Vegetarians, vegans, and those with certain medical conditions may need fortified foods or supplements.

Good sources include meat (especially beef liver), fish (tuna, salmon), eggs, milk, cheese, and fortified foods like certain breakfast cereals and nutritional yeast.

Yes, correcting a vitamin B12 deficiency can lead to symptomatic improvement in individuals with severe diabetic neuropathy, especially for symptoms like pain and tingling.