Should I be worried about high folate levels?

January 2, 2026 •

4 min read

Since 1998, the U.S. has mandated folic acid fortification in grain products, significantly increasing population-wide intake. This practice, alongside supplement use, prompts a critical question: should I be worried about high folate levels?

Quick Summary

Excessive intake of synthetic folic acid, often from supplements and fortified foods, can lead to elevated blood folate. A primary risk is the potential for high levels to mask a serious vitamin B12 deficiency, concealing neurological damage. Managing intake, distinguishing folate sources, and regular testing are crucial.

Key Points

Differentiate Folate vs. Folic Acid: Natural folate from food is safe in high amounts, whereas excess synthetic folic acid from supplements and fortified foods can accumulate and pose risks.
Masking B12 Deficiency: The most serious risk of high folic acid is its ability to correct the anemia of a B12 deficiency while allowing silent, irreversible neurological damage to progress.
Monitor Supplement Intake: Excessive supplementation is the primary cause of high levels. Check all your supplements for folic acid content to avoid exceeding the 1,000 mcg/day upper limit.
Test B12 and Folate Together: If high folate is detected, it is essential to also test vitamin B12 levels to rule out an underlying deficiency.
Manage Through Diet: To reduce high levels, focus on natural folate sources and minimize intake of heavily fortified processed foods.
Consult a Doctor: Always consult a healthcare provider before stopping or starting supplementation, especially if you are pregnant, have a medical condition, or take other medications.

What Is the Difference Between Folate and Folic Acid?

To understand the concerns associated with high folate, it's vital to differentiate between the two primary forms of vitamin B9: naturally occurring folate and synthetic folic acid.

Natural Folate: This form is found organically in foods like leafy greens, legumes, and eggs. It's less stable and less readily absorbed by the body. The body processes it quickly, so it does not accumulate to harmful levels.
Synthetic Folic Acid: This is the version added to supplements and fortified foods. It is more stable and has a higher absorption rate (approximately 85% compared to 50% for food folate). This form requires a metabolic process involving the liver to become biologically active. The liver's capacity to process folic acid is limited, meaning excess can build up in the bloodstream as 'unmetabolized folic acid' (UMFA).

Key Causes of Elevated Folate Levels

High folate levels are not typically caused by eating a folate-rich diet alone. The main culprits are excessive supplementation and high consumption of fortified foods.

Excessive Supplementation: The most common cause is taking too many supplements. This could be a multivitamin, a B-complex vitamin, and a separate folic acid supplement all at once. The Tolerable Upper Intake Level (UL) for adults from fortified foods and supplements is 1,000 mcg per day.
Fortified Foods: Cereal grains, flour, and pasta in many countries are fortified with folic acid to prevent neural tube defects. Consistent and high consumption of these products, in addition to supplements, can push total intake beyond optimal levels.
Medical Conditions: Underlying conditions like kidney disease can impair the body's ability to excrete water-soluble vitamins, including folate, leading to accumulation. A vitamin B12 deficiency can also cause folate to become 'trapped' in an unusable form, resulting in elevated serum folate levels.

Symptoms and Potential Risks of High Folic Acid

While natural folate from food is largely benign, high levels of unmetabolized folic acid carry several documented risks, particularly concerning its interaction with vitamin B12.

Masking Vitamin B12 Deficiency: This is the most serious risk. High folic acid can correct the anemia associated with a B12 deficiency, masking this key diagnostic symptom. The underlying B12 deficiency, however, continues to cause potentially irreversible neurological damage. This can manifest as numbness, tingling, and cognitive decline.
Accelerated Cognitive Decline: In older adults with low vitamin B12 levels, excess folic acid intake has been linked to an increased rate of mental decline.
Neurological Side Effects: High doses of folic acid have been associated with irritability, sleep disturbances, and confusion.
Potential Cancer Concerns: Some studies have suggested that high doses of folic acid could promote the growth of existing precancerous or cancerous cells. However, research is mixed and the link remains inconclusive. Natural folate from food is not associated with this risk.
Drug Interactions: High doses can interfere with certain medications used for seizures, cancer, and other conditions.

Management of High Folate Levels

If a blood test reveals high folate, the primary steps involve assessing and modifying intake.

Assess all sources: Review all supplements (multivitamins, B-complex, etc.) and fortified foods. Many people are unaware they are consuming folic acid from multiple sources.
Reduce/stop supplementation: Under medical supervision, reduce or temporarily stop taking folic acid supplements. Since it is water-soluble, levels typically return to normal within a few weeks.
Check B12 levels: It is crucial to test both B12 and folate together, especially in older adults or those with risk factors.
Prioritize natural sources: Focus on a diet rich in natural folate from whole foods rather than relying on synthetic supplements or heavily fortified products.
Consider alternative supplements: For those needing B9 supplementation, the active form, L-5-methyltetrahydrofolate (L-5-MTHF), may be a better option as it does not accumulate as readily and is less likely to mask a B12 deficiency.

Comparison of Natural Folate and Synthetic Folic Acid


Feature	Natural Folate (from food)	Synthetic Folic Acid (from supplements/fortified food)
Absorption Rate	Lower (approx. 50%)	Higher (approx. 85%)
Metabolism	Processed directly by the intestines	Converted by the liver; excess can remain unmetabolized
Bioavailability	Less stable, can be destroyed by cooking	Stable and readily absorbed
Upper Limit (UL)	No established UL; generally considered safe in high amounts	Adult UL of 1,000 mcg/day to avoid masking B12 deficiency
Health Risk of Excess	Extremely low risk of toxicity	Potential to mask B12 deficiency; linked to other risks

Conclusion

While a low folate intake is a serious concern, particularly for women of childbearing age, an excess of synthetic folic acid is also not benign. The risk of masking a vitamin B12 deficiency is the most significant danger, potentially leading to irreversible neurological damage. High folate levels are not typically a concern from dietary sources alone. Anyone concerned about high folate, particularly those taking supplements or consuming many fortified foods, should consult a healthcare provider. A comprehensive blood test checking both folate and vitamin B12 is the first step toward proper management and peace of mind.

Visit the NIH Office of Dietary Supplements for more information on folate.

Frequently Asked Questions

No, it is extremely difficult to get high folate levels from consuming natural food sources alone, as the body processes them differently than synthetic folic acid.

High folic acid can hide the anemia that signals a B12 deficiency, so you won't see the usual blood test changes. However, neurological symptoms like numbness, tingling, and memory issues might still occur. A blood test for both folate and B12 is the only way to be sure.

While often asymptomatic, high folic acid can sometimes cause side effects like nausea, bloating, sleep disturbances, irritability, and confusion. If a B12 deficiency is masked, more severe neurological issues can arise.

Treatment usually involves reviewing and reducing the intake of folic acid from supplements and fortified foods under a doctor's supervision. It is also crucial to test and treat for an underlying vitamin B12 deficiency if present.

Because folate is a water-soluble vitamin, excess amounts are excreted through urine. After reducing intake, levels typically normalize within a few weeks, though this depends on kidney function and individual metabolism.

The active form, L-5-methyltetrahydrofolate (L-5-MTHF), or methylfolate, does not accumulate as readily as synthetic folic acid and is considered less likely to mask a B12 deficiency.

For adults, the Tolerable Upper Intake Level (UL) for synthetic folic acid from supplements and fortified foods is 1,000 mcg per day. There is no established UL for natural folate from food.

Individuals who take high-dose supplements, consume many fortified foods, have impaired kidney function, or have an undiagnosed vitamin B12 deficiency are most at risk for elevated folate.