Can You Get Too Much Folic Acid? Understanding the Risks

December 28, 2025 •

3 min read

The Tolerable Upper Intake Level for folic acid in adults is 1,000 micrograms (1 mg) per day. While this synthetic form of vitamin B9 is essential for health, especially during pregnancy, exceeding this limit raises a critical question: can you get too much folic acid, and what are the potential consequences?

Quick Summary

Yes, you can get too much folic acid, primarily from supplements and fortified foods. This can mask a vitamin B12 deficiency and cause other side effects.

Key Points

Tolerable Upper Limit (UL): For most adults, the safe upper limit for folic acid is 1,000 mcg (1 mg) per day, a dose that can be exceeded by combining supplements and fortified foods.
Masks B12 Deficiency: Excessive folic acid can correct the anemia associated with vitamin B12 deficiency while allowing serious, irreversible nerve damage to continue undetected.
Natural vs. Synthetic: You cannot get too much natural folate from food, but you can overdo it with synthetic folic acid from supplements and fortified products.
Potential Risks: High folic acid intake is associated with side effects like stomach issues and irritability, and some studies suggest links to altered immune function, cancer risk, and developmental issues in offspring.
At-Risk Groups: The elderly, individuals with the MTHFR gene variant, and pregnant women should be particularly mindful of their folic acid intake and consult a healthcare professional.
Prioritize Natural Sources: The best way to get sufficient vitamin B9 is by consuming a variety of folate-rich foods like leafy greens and legumes, minimizing reliance on high-dose supplements.

What Is the Difference Between Folate and Folic Acid?

Folate is the natural form of vitamin B9 found in foods such as leafy green vegetables, citrus fruits, and legumes. It is water-soluble, and the body eliminates any excess easily. Folic acid is the synthetic version added to supplements and fortified foods. The body metabolizes folic acid more slowly, mainly in the liver. Genetic variations, such as the MTHFR polymorphism, can affect this process, potentially causing unmetabolized folic acid to build up in the bloodstream. It is this synthetic form, not natural folate, that is linked to potential health issues.

The Major Risk: Masking a Vitamin B12 Deficiency

High folic acid intake can mask a vitamin B12 deficiency, a significant risk. Both nutrients are vital for red blood cell production. While high folic acid can correct the anemia caused by B12 deficiency, it hides the underlying problem, allowing nerve damage to progress silently and potentially irreversibly. Older adults face a higher risk due to reduced natural B12 absorption. Symptoms of B12 deficiency include tingling, numbness, and cognitive issues.

Other Side Effects of High Folic Acid Doses

Exceeding the 1,000 mcg daily UL for folic acid can lead to several adverse effects. Symptoms may include gastrointestinal upset, loss of appetite, irritability, confusion, difficulty sleeping, skin reactions, and rarely, seizures.

Concerns for Specific Populations and Conditions

Certain groups require particular attention regarding folic acid intake:

Pregnancy and Childhood Development: While crucial for preventing neural tube defects, excessive folic acid during pregnancy may be associated with potential negative outcomes for the child, including impaired cognitive development and a higher risk of autism spectrum disorder (ASD). Excess prenatal folic acid may also be linked to increased risk of insulin resistance, diabetes, and obesity in offspring. The UL for pregnant women is 1,000 mcg daily for those over 18 and 800 mcg for those under 18.
Cancer Risk: Research on high folic acid intake and cancer is ongoing and complex. Some studies suggest high daily doses (e.g., 0.8-1.2 mg) might increase the risk of certain cancers. Individuals with a history of cancer should consult a healthcare provider before taking high doses.
Genetic Factors: People with the MTHFR C677T gene polymorphism may have a reduced ability to process folic acid effectively, potentially leading to higher levels of unmetabolized folic acid and associated risks. Considering alternatives like 5-MTHF may be beneficial for these individuals.

How to Avoid Excessive Folic Acid Intake

It's unlikely to consume too much natural folate from food alone. The risk arises from combining fortified foods and supplements. Strategies to manage intake include prioritizing food sources, monitoring fortified foods, and evaluating supplement needs. Individuals at risk for B12 deficiency should have regular blood tests.

Folate vs. Folic Acid: A Comparison


Feature	Folate (Natural)	Folic Acid (Synthetic)
Source	Naturally found in foods like leafy greens, beans, and oranges	Found in supplements and fortified foods like bread, cereal, and pasta
Absorption	Processed in the small intestine	Metabolized more slowly in the liver and other tissues
Bioavailability	Lower absorption rate than folic acid; some lost during cooking	Highly bioavailable and stable; more readily absorbed by the body
Risk of Excess	No known risk of toxicity from naturally occurring folate	High doses can accumulate in the bloodstream and have adverse effects
Primary Function	Supports general health, red blood cell production, and cell growth	Crucial for preventing neural tube defects; used to treat deficiencies

Conclusion

While essential for preventing birth defects and overall health, it is possible to consume too much folic acid, primarily from supplements and fortified foods. The most significant concern is its ability to mask a vitamin B12 deficiency, potentially leading to severe and irreversible neurological damage. There are also other potential side effects and concerns related to pregnancy and cancer risk. Being mindful of all sources of intake and prioritizing natural food sources of folate can help maintain a healthy balance. Always consult a healthcare professional for personalized guidance, particularly for pregnant women or those with pre-existing health conditions.

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

Frequently Asked Questions

For most adults, the Tolerable Upper Intake Level (UL) is 1,000 micrograms (1 mg) of folic acid per day from supplements and fortified foods. However, some conditions may require different doses, which should be determined by a doctor.

No, it is highly unlikely to get too much folate from consuming foods that naturally contain it, such as leafy greens, legumes, and fruits. The body can easily excrete excess folate that comes from natural food sources.

Excess folic acid can correct the anemia that is a symptom of B12 deficiency, effectively masking the problem. This allows the underlying B12 deficiency to continue causing silent, and potentially irreversible, neurological damage.

Symptoms can include gastrointestinal issues like nausea and bloating, irritability, confusion, sleep problems, and skin reactions. In very high doses, it can even provoke seizures in susceptible individuals.

Yes. Research suggests very high folic acid intake during pregnancy may be linked to adverse effects in the child, such as impaired cognitive development and an increased risk of autism spectrum disorder (ASD). Pregnant women should follow their doctor’s specific dosage recommendations.

Folate from food is metabolized directly in the small intestine, whereas synthetic folic acid requires a slower, multi-step conversion process, primarily in the liver. This can lead to the accumulation of unmetabolized folic acid in the bloodstream.

Older adults and individuals with an untreated vitamin B12 deficiency are at risk for neurological damage. People with specific genetic mutations, such as the MTHFR variant, may also be more susceptible due to reduced metabolic capacity.