Does taking folic acid raise B12 levels?

January 6, 2026 •

4 min read

An estimated 20% of adults over 60 experience vitamin B12 deficiency in the United States, which can be dangerously hidden by high folic acid intake. While both are essential B vitamins, taking folic acid does not increase B12 levels and can, in fact, complicate the diagnosis of a B12 deficiency. This phenomenon can have serious, long-term health consequences if not properly understood.

Quick Summary

Taking folic acid does not raise vitamin B12 levels; instead, high folic acid intake can conceal the signs of a B12 deficiency, worsening neurological damage. The two vitamins have an intricate relationship in the body's metabolic processes. It is vital to test B12 levels before supplementing folic acid to avoid health complications.

Key Points

Folic Acid Does Not Raise B12: Folic acid supplements do not directly increase vitamin B12 levels and cannot correct a B12 deficiency.
Masking Effect: High doses of folic acid can mask the megaloblastic anemia caused by a B12 deficiency, preventing early detection.
Risk of Neurological Damage: When a B12 deficiency is masked by folic acid, neurological damage can continue and worsen undetected, potentially becoming irreversible.
Dual Function: Both vitamins are critical for one-carbon metabolism, but B12 plays a unique and essential role in maintaining nervous system health.
Crucial Diagnostic Step: Healthcare providers should always test a patient's B12 levels before beginning high-dose folic acid treatment to avoid the masking effect.
At-Risk Groups: Individuals who are older, vegan, or have gastrointestinal issues should be especially vigilant and test for B12 deficiency before taking folic acid supplements.

The Intricate Metabolic Relationship Between Folic Acid and B12

To understand why taking folic acid does not raise B12 levels, one must first grasp the close metabolic relationship between these two vital B-vitamins. They are both crucial for one-carbon metabolism, a process essential for DNA synthesis and repair, cell division, and the regeneration of the amino acid methionine from homocysteine. In this process, the B12-dependent enzyme methionine synthase converts homocysteine to methionine, using the active form of folate (5-methyltetrahydrofolate) as a co-factor.

When there is a vitamin B12 deficiency, the enzyme methionine synthase is impaired. This leads to a buildup of 5-methyltetrahydrofolate, trapping folate in a form that cannot be used for DNA synthesis, a phenomenon known as the 'methylfolate trap'. This functional folate deficiency mimics the effects of a true folate deficiency, causing megaloblastic anemia—the presence of abnormally large, immature red blood cells.

Masking and Exacerbation: The Danger of High Folic Acid Intake

Here is where the key distinction lies. Taking a high dose of supplemental folic acid can effectively bypass the 'methylfolate trap' by providing the body with enough folate to proceed with red blood cell synthesis, thus correcting the anemia. However, this action does not fix the underlying B12 deficiency that caused the trap in the first place. This is known as the 'masking effect'.

Crucially, this masking is considered dangerous because it removes the most common and obvious symptom of B12 deficiency (anemia), while allowing the neurological damage associated with the deficit to continue progressing undetected. Studies have also indicated that high serum folate levels, in the presence of low B12, may even exacerbate neurological decline. The damage to the nervous system from untreated B12 deficiency can be severe and permanent.

Why High Folic Acid Does Not Fix Low B12

Different Functions: While they work together, each vitamin performs unique, independent functions. B12 is specifically required for neurological health and the metabolism of methylmalonic acid (MMA).
Holotranscobalamin Depletion: Research suggests that excessive folic acid can deplete holotranscobalamin (holoTC), the active transport protein for B12 in the blood. This reduces the delivery of B12 to nerve cells and other tissues.
Folate vs. B12 Absorption: The mechanisms for absorbing folic acid from supplements and B12 from food and supplements are different. Deficiencies often arise from malabsorption issues that prevent B12 from being properly processed, a problem folic acid cannot fix.
Methylmalonic Acid (MMA) Elevation: Unlike folate deficiency, B12 deficiency causes an accumulation of MMA. While high folic acid can normalize homocysteine, it has no effect on elevated MMA, a specific marker of B12 status.

Comparing Folic Acid and B12 Deficiency Symptoms

Understanding the distinction is key to proper diagnosis and treatment. A comparison of symptoms can be helpful, but blood tests are always necessary.


Symptom Category	Folic Acid Deficiency	Vitamin B12 Deficiency
Hematological	Megaloblastic anemia, fatigue, weakness.	Megaloblastic anemia, fatigue, weakness.
Neurological	Generally absent, though neuropsychiatric symptoms can occur.	Numbness, tingling (paresthesia), balance issues, memory loss, cognitive decline, depression.
Gastrointestinal	Sore tongue (glossitis), diarrhea.	Sore tongue (glossitis), nausea, decreased appetite.
Diagnostic Markers	Low serum folate, high homocysteine, normal MMA.	Low serum B12, high homocysteine, high MMA.

The Role of Testing and Supplementation Strategies

To prevent the masking effect, medical professionals will almost always check B12 levels before prescribing high-dose folic acid. For at-risk individuals, such as the elderly, vegans, or those with digestive disorders like pernicious anemia, this check is a critical step. Many governments, including the US, fortify grain products with folic acid, which has been successful in reducing folate deficiency. However, this also means many people consume more folic acid than they realize, making proper monitoring even more important for those at risk for low B12.

If a deficiency in both vitamins is identified, treatment is typically initiated with B12 before or alongside folic acid to prevent the neurological complications from worsening. In cases of malabsorption, B12 injections may be necessary.

Conclusion: Prioritize Diagnosis Before Supplementation

In conclusion, taking folic acid does not increase your B12 levels. The interaction between the two vitamins is complex, and supplementing with high doses of folic acid can dangerously mask a coexisting B12 deficiency by treating the anemia without addressing the root cause. This delay in diagnosis can allow irreversible nerve damage to occur. Therefore, it is crucial to consult a healthcare provider for proper diagnosis, especially if you belong to an at-risk group, to ensure that any supplementation strategy is safe and effective. Testing for vitamin B12 levels before initiating folic acid treatment is a standard and necessary precaution. For more information, you can review the National Institutes of Health (NIH) information on Vitamin B12.

Frequently Asked Questions

Folic acid can mask a B12 deficiency by correcting the megaloblastic anemia (large, immature red blood cells) that is a common symptom of both deficiencies. By normalizing the blood count, it removes a major warning sign, allowing the B12-specific neurological damage to continue unchecked.

The 'methylfolate trap' is a metabolic process that occurs in B12 deficiency. Without enough B12, the body cannot use the 5-methyltetrahydrofolate (the active form of folate), trapping it and leading to a functional folate deficiency. Folic acid supplementation can bypass this trap to correct anemia, but it does not resolve the root B12 issue.

Yes, taking B12 and folic acid together is safe and often recommended, especially for deficiencies involving both vitamins. Starting B12 supplementation before or concurrently with folic acid ensures that any underlying B12 deficiency is addressed and not masked.

Individuals at high risk include older adults, vegans, vegetarians, and those with conditions affecting nutrient absorption like pernicious anemia, celiac disease, or atrophic gastritis.

Neurological symptoms include numbness and tingling in the hands and feet, memory loss, balance problems, depression, and confusion. These can worsen if a B12 deficiency goes untreated while taking folic acid.

Yes, chronic, high intake of folic acid, especially in individuals with an undiagnosed B12 deficiency, can be detrimental. It can worsen neurological symptoms and has been linked to other health concerns in some studies.

A doctor can order specific blood tests to measure the levels of both vitamins, as well as markers like homocysteine and methylmalonic acid (MMA). Elevated MMA is a specific indicator of B12 deficiency, while elevated homocysteine can occur with both deficiencies.