What happens if I eat too much folic acid?

January 6, 2026 •

4 min read

According to the NIH, the Tolerable Upper Intake Level for folic acid for adults is 1,000 micrograms per day, an amount easily exceeded by those taking high-dose supplements in addition to fortified foods. This raises serious questions about what happens if you eat too much folic acid and its potential health consequences.

Quick Summary

Excessive intake of synthetic folic acid, primarily from high-dose supplements and fortified foods, can mask a vitamin B12 deficiency and potentially worsen neurological issues, particularly in older adults.

Key Points

Masks B12 Deficiency: Excessive folic acid can correct the anemia of a B12 deficiency while neurological damage progresses silently.
Risks for Elderly: Older adults, who often have low B12, are especially vulnerable to cognitive decline if they have high folic acid levels.
UMFA Accumulation: The body's inability to metabolize large doses of synthetic folic acid leads to the accumulation of unmetabolized folic acid (UMFA) in the blood.
Pregnancy Concerns: Excess folic acid during pregnancy may be linked to developmental issues in children, including slower brain development and higher risks of insulin resistance and autism.
Side Effects: High doses can cause a range of symptoms, including nausea, bloating, confusion, irritability, and skin reactions.
Cancer Risk: Some studies suggest that high folic acid intake might increase the risk or accelerate the progression of certain cancers, especially colorectal.

Understanding Folic Acid vs. Natural Folate

Before delving into the consequences of excessive intake, it's crucial to distinguish between folate and folic acid. Folate is the naturally occurring form of vitamin B9 found in foods like leafy greens, beans, and citrus fruits. Folic acid, on the other hand, is the synthetic, man-made version added to supplements and fortified foods, such as bread, cereal, and pasta. While the body can easily process folate from natural sources, it metabolizes folic acid differently and less efficiently. This key difference is why problems typically arise from consuming too much folic acid, not too much natural folate.

The Body's Conversion Challenge

Folic acid must undergo conversion by the liver and other tissues into its active form, 5-MTHF, to be used by the body. When intake exceeds the liver's capacity to convert it, unmetabolized folic acid (UMFA) accumulates in the bloodstream. High levels of UMFA have been linked to several adverse health effects, which are not seen with high dietary intake of natural folate.

The Critical Risk: Masking a Vitamin B12 Deficiency

One of the most significant and dangerous outcomes of consuming too much folic acid is its ability to conceal a vitamin B12 deficiency. Both folate and vitamin B12 deficiencies can cause megaloblastic anemia, a condition characterized by enlarged red blood cells. Because folic acid can correct the anemia associated with a B12 deficiency, it can mask this symptom, leading to a delayed diagnosis. This is extremely dangerous because, while the anemia is corrected, the nerve damage caused by the underlying B12 deficiency can progress silently and become irreversible.

This risk is particularly pronounced in older adults, who are more susceptible to B12 deficiencies due to impaired absorption. Early detection and treatment of B12 deficiency are critical to prevent severe and permanent neurological damage.

Common Side Effects of High Folic Acid Doses

While natural folate from food is generally harmless, taking high doses of folic acid supplements (often exceeding 1,000 mcg per day) can lead to a range of unpleasant side effects. These symptoms may indicate that your intake is too high and should be addressed with a healthcare provider.

Gastrointestinal Issues: Nausea, bloating, stomach cramps, and gas are common digestive complaints. A bitter or unpleasant taste in the mouth may also occur.
Neurological Symptoms: Excessive intake can cause irritability, confusion, and other behavioral changes. In severe cases, high doses have been linked to seizures, particularly in individuals with pre-existing seizure disorders.
Cognitive Decline: Several studies have linked high plasma folate levels to accelerated age-related mental decline, especially in seniors with low vitamin B12 status.
Skin Reactions: Allergic responses, though rare, can manifest as a skin rash, itching, or redness. In very rare instances, a severe allergic reaction (anaphylaxis) has been reported.

Long-Term and Population-Specific Risks

Beyond the more immediate side effects, research has explored potential long-term risks, particularly for certain groups. The evidence is still evolving, but several areas of concern have been identified.

Excessive Folic Acid During Pregnancy

While adequate folic acid intake is crucial for preventing neural tube defects, excessive amounts may be harmful. Some studies suggest that taking over 1,000 mcg of folic acid per day during the periconceptional period could negatively impact a child's brain development, increase the risk of autism, and raise the chances of insulin resistance later in life. It is essential for pregnant women to follow their doctor's guidance on supplementation.

The Link to Cancer Risk

The relationship between folic acid and cancer is complex. Some research indicates that while adequate folate intake might protect against certain cancers, high-dose folic acid supplementation could potentially increase the risk or progression of existing cancers, such as colorectal cancer. This is thought to be because high levels of folic acid may help pre-existing cancer cells grow and spread. More research is needed to clarify this link, but it's a concern for individuals with a history of cancer.

Folic Acid vs. Folate Comparison


Feature	Folic Acid	Folate
Source	Synthetic (man-made), found in supplements and fortified foods.	Natural, found in fruits, vegetables, beans, and leafy greens.
Absorption	More easily and efficiently absorbed by the body.	Less efficiently absorbed and sensitive to heat/light.
Metabolism	Requires conversion by the liver; can lead to unmetabolized folic acid (UMFA) at high doses.	Absorbed directly and used by the body more naturally.
Upper Intake Level (UL)	Has a Tolerable UL of 1,000 mcg for adults due to masking B12 deficiency.	No established UL for food-based folate.
Side Effects	High doses can cause nausea, confusion, seizures, and other issues.	Safe even at high dietary intakes; no reported side effects from food.

Conclusion: Navigating Folic Acid Safely

While folic acid is a vital nutrient, particularly for preventing neural tube defects in early pregnancy, it is not without risks when consumed in excess. The potential to mask a vitamin B12 deficiency and worsen neurological damage is a serious concern, especially for older adults. Furthermore, high intake during pregnancy and a possible link to increased cancer risk in some populations underscore the importance of moderation and informed supplementation. The most effective strategy is to obtain vitamin B9 primarily from a diet rich in natural folate sources, only supplementing with folic acid as recommended by a healthcare professional. Women of childbearing age should consult their doctor to determine the appropriate dosage to reduce risks while gaining the benefits. For more detailed information on folate intake, consult the National Institutes of Health fact sheet at the following authoritative link: Folate - Consumer - NIH Office of Dietary Supplements.

By prioritizing dietary sources and using supplements judiciously, individuals can ensure they receive adequate vitamin B9 without risking the potential adverse effects associated with excessive folic acid.

Frequently Asked Questions

No, it is nearly impossible to consume too much of the naturally occurring folate found in food sources like leafy green vegetables, citrus fruits, and beans.

For adults, the Tolerable Upper Intake Level (UL) for synthetic folic acid is 1,000 micrograms (1 mg) per day, a threshold set to prevent the masking of vitamin B12 deficiency.

Older adults and individuals with an undiagnosed vitamin B12 deficiency are at the highest risk, as are pregnant women and those with a history of cancer.

UMFA is synthetic folic acid that the body has not converted into its active form. It can build up in the bloodstream when intake from supplements and fortified foods is too high, leading to potential health issues.

Newer nutrition labels often use 'mcg DFE' (dietary folate equivalents) for total folate and list 'folic acid (in mcg)' separately in parentheses if it is included.

No, pregnant women and those trying to conceive are typically advised to take folic acid to prevent neural tube defects. They should, however, follow their doctor's dosage recommendations to avoid excess intake.

In individuals with pre-existing seizure disorders, high doses of folic acid may worsen seizures and can also interfere with anti-seizure medication.

To reduce intake, you can limit fortified foods and switch to a lower-dose supplement or a supplement containing the methylated form of folate instead. Always consult a healthcare provider before changing your regimen.