What is considered a high level of folate?

November 16, 2025 •

4 min read

According to health guidelines, elevated serum folate levels are generally considered to be above 20 nanograms per milliliter (ng/mL). The primary concerns with having a high level of folate often arise not from dietary intake, but from overconsumption of synthetic folic acid supplements, which can mask an underlying vitamin B12 deficiency.

Quick Summary

This article defines what constitutes high folate levels based on serum and red blood cell measurements. It covers the causes of elevated folate, such as excessive supplementation and certain medical conditions, and details the associated health risks. The piece also provides guidance on safe intake and when to consult a healthcare provider.

Key Points

High Serum Folate: Levels consistently above 20 nanograms per milliliter (ng/mL) are considered elevated, often indicating excessive synthetic folic acid intake.
RBC Folate: Red blood cell folate provides a longer-term picture, with normal ranges around 140 to 628 ng/mL.
Masking B12 Deficiency: A major risk of high folate is masking the anemia associated with a vitamin B12 deficiency, allowing neurological damage to progress unnoticed.
Causes of High Levels: Primary causes include overuse of synthetic folic acid supplements, excessive fortified food consumption, and underlying conditions like kidney disease or unaddressed B12 deficiency.
Management: To manage high levels, a healthcare provider will likely recommend reducing or stopping supplements, favoring natural food sources, and checking B12 levels.

What Defines a High Folate Level?

Understanding what constitutes a high level of folate first requires a look at the different ways it is measured. Clinical assessments primarily use serum folate and red blood cell (RBC) folate levels. Serum folate reflects short-term intake and can fluctuate with recent meals, whereas RBC folate provides a more accurate picture of long-term status.

For serum folate, levels above 20 ng/mL are typically considered elevated, with some labs noting values exceeding 24 ng/mL as definitively high. The normal range generally falls between 2.7 and 17.0 ng/mL. For RBC folate, which indicates longer-term status, the normal range is approximately 140 to 628 ng/mL, and levels significantly above this may signal an issue. It is crucial to interpret these results in conjunction with vitamin B12 status and other clinical symptoms, as one can affect the other.

Primary Causes of Elevated Folate Levels

The most common cause of elevated folate is an excessive intake of synthetic folic acid, not natural folate from food. Folic acid is used in supplements and is also added to fortified grain products, such as cereals, bread, and pasta, as part of public health initiatives to prevent neural tube defects.

Reasons for elevated folate often include:

Excessive supplementation: Many people take multiple supplements containing folic acid, such as a multivitamin, a B-complex, and an additional prenatal or folic acid pill, leading to unintentional overconsumption.
Fortified foods: Regularly consuming heavily fortified cereals and bread alongside supplements can push overall intake beyond safe levels.
Vitamin B12 deficiency: A serious issue known as the "methyl-folate trap" can occur when B12 levels are low. In this scenario, folate becomes trapped in a form the body cannot use, causing it to build up in the blood while the B12 deficiency remains masked.
Medical conditions: Certain conditions, such as chronic kidney disease, can impair the body's ability to excrete excess water-soluble vitamins like folate, leading to accumulation.
Medications: Some drugs, including methotrexate and certain anti-seizure medications, can interfere with folate metabolism, sometimes leading to higher levels.

The Risks Associated with High Folate

While the human body typically excretes excess water-soluble folate in urine, persistently high levels can pose several health risks, with the most significant being its effect on vitamin B12 status.

Masking Vitamin B12 Deficiency This is the most critical risk. High levels of folic acid can correct the anemia associated with a B12 deficiency, but they do not address the neurological damage caused by the lack of B12. This can allow irreversible nerve damage, cognitive decline, and other serious issues to progress unnoticed until it is too late. This is why testing for both folate and B12 together is recommended.

Cognitive and Neurological Effects High folate levels, especially when coupled with low B12, have been linked to an accelerated decline in cognitive function in older adults. The presence of unmetabolized folic acid in the bloodstream has also been a subject of research regarding its potential neurological effects, though more study is needed.

Potential Cancer Concerns Some studies suggest a complex relationship between high folic acid intake and cancer risk. While adequate folate is protective, high levels of synthetic folic acid may promote the growth of existing pre-cancerous or cancerous cells. The research is mixed and ongoing, but some studies point to an increased risk of certain cancers, such as prostate and colorectal cancer, in individuals with very high folic acid intake.

Comparing Folate from Food vs. Supplements


Feature	Natural Folate (from food)	Synthetic Folic Acid (from supplements/fortification)
Absorption	Regulated by the body; absorption efficiency decreases as intake increases.	Absorbed more easily and consistently than natural folate.
Toxicity Risk	Extremely low risk of toxicity from food sources alone.	High doses can lead to unmetabolized folic acid (UMFA) and health concerns.
Chemical Form	Found in various active forms (e.g., 5-MTHF).	Must be converted by the body into its active forms.
Effect on B12	Does not mask B12 deficiency in the same way as high folic acid.	Can mask megaloblastic anemia, allowing B12 deficiency to go untreated.
Upper Limit (UL)	No established UL for natural folate from food.	UL of 1,000 mcg per day for adults from supplements and fortified foods.

Managing Elevated Folate Levels

If a blood test reveals high folate levels, the first step is to consult a healthcare provider to review supplement intake and test for vitamin B12 deficiency. Management strategies typically include:

Reducing Folic Acid Supplements: Discontinue or lower the dose of multivitamins, B-complex supplements, and standalone folic acid pills. For pregnant women or those with specific health needs, a healthcare provider should guide any changes.
Limiting Fortified Foods: Reduce consumption of heavily fortified grain products if intake is already high from supplements.
Focusing on Natural Folate: Prioritize natural folate from whole foods like dark leafy greens, legumes, and citrus fruits. The body regulates the absorption of natural folate more effectively, making overconsumption less of a concern.
Considering Methylfolate: In some cases, switching to the active form of folate (L-5-methyltetrahydrofolate or 5-MTHF) may be beneficial, as it doesn't accumulate as readily and doesn't mask B12 deficiency.

Conclusion

While folate is a vital nutrient for health, more is not always better. A high level of folate, typically from excessive synthetic folic acid intake, can pose real risks, most notably masking a dangerous vitamin B12 deficiency. Understanding the difference between natural folate and synthetic folic acid, carefully monitoring your supplement intake, and working with a healthcare professional are essential steps to ensure optimal B-vitamin balance without risking the potential pitfalls of excess. Regular testing for both folate and B12 is recommended for individuals at risk of high folate levels, such as those taking multiple supplements or with underlying health conditions. By taking a thoughtful and balanced approach, individuals can maintain sufficient folate status safely.

Is high folate a problem? - SiPhox Health

Frequently Asked Questions

A high serum folate level is generally considered to be above 20 nanograms per milliliter (ng/mL), though this can vary slightly depending on the laboratory. Results should always be interpreted by a healthcare professional in the context of other factors.

The most common causes include consuming high-dose folic acid supplements, taking multiple supplements that contain folic acid, and eating a diet rich in fortified foods. Medical conditions like vitamin B12 deficiency and kidney disease can also cause elevated levels.

Yes, persistently high folate levels, typically from supplements, are concerning because they can mask the signs of a serious vitamin B12 deficiency. This can lead to delayed diagnosis and irreversible neurological damage.

It is extremely rare to achieve harmful folate levels from food alone. The body regulates the absorption of natural folate from food more effectively than synthetic folic acid.

High folic acid intake can correct the megaloblastic anemia that often signals a B12 deficiency. By correcting the anemia, it hides the most visible symptom, allowing the underlying neurological damage from the B12 deficiency to progress silently.

Some individuals may experience digestive upset, sleep problems, irritability, confusion, or difficulty concentrating. If high folate is masking a B12 deficiency, tingling or numbness in the extremities may also occur.

To lower your levels, you should first consult a healthcare provider. They will likely recommend reducing or stopping folic acid supplements and limiting your intake of fortified foods. Prioritizing natural folate from whole foods is a safer approach.