What Happens If Your Folate Levels Are Too High?

November 14, 2025 •

4 min read

While folate is an essential B-vitamin, studies show that excessively high intake, especially from synthetic folic acid, can pose serious health risks. This can be particularly dangerous when it masks an underlying vitamin B12 deficiency, which can lead to permanent neurological damage if left untreated.

Quick Summary

Excessive folate levels, often from synthetic folic acid, can mask a vitamin B12 deficiency and potentially cause neurological issues. This overview details the risks, common symptoms, and how to manage high folate intake safely.

Key Points

Masks B12 Deficiency: High folate can hide the anemia of a B12 deficiency, allowing permanent neurological damage to progress unnoticed.
Digestive Issues: Excessive folic acid intake is associated with side effects like nausea, bloating, and loss of appetite.
Neurological Symptoms: High levels can cause confusion, irritability, and sleep disturbances.
Cancer Concerns: Some research suggests a link between excessive folic acid and an increased risk of certain cancers, though findings are mixed.
Source Matters: Natural folate from food is safe at high levels, but synthetic folic acid from supplements and fortified foods can accumulate and cause issues.
Cognitive Decline Risk: High folate in conjunction with low B12 may accelerate age-related cognitive decline in older adults.

The Critical Difference: Folate vs. Folic Acid

Before exploring the risks, it's crucial to distinguish between naturally occurring folate and its synthetic counterpart, folic acid. Folate is found in foods like leafy greens, beans, and oranges, and is generally not associated with adverse effects from high intake. Folic acid, however, is a man-made version added to fortified foods and found in many supplements. The body metabolizes folic acid differently, and excessive amounts can lead to a buildup of unmetabolized folic acid (UMFA) in the bloodstream, which is linked to several health concerns.

The Silent Danger: Masking Vitamin B12 Deficiency

One of the most significant dangers of high folate levels, particularly from folic acid, is its ability to mask a vitamin B12 deficiency. Folate and B12 work together closely in the body. When B12 levels are low, a person can develop megaloblastic anemia, a condition characterized by enlarged red blood cells. Supplementing with high doses of folic acid can correct this anemia, making it appear that the deficiency is resolved. However, this treatment does not address the underlying B12 problem. If the B12 deficiency goes undiagnosed and untreated, the neurological damage can continue to progress silently, leading to serious and irreversible consequences. This is especially concerning in older adults, who are already at a higher risk for poor B12 absorption.

Potential Neurological Consequences

Permanent nerve damage
Cognitive decline and memory problems
Balance issues
Exacerbated neurological symptoms in those with pre-existing low B12

Causes of Excessive Folate Levels

High folate levels typically result from overconsumption of synthetic folic acid rather than natural food folate. Common sources include:

High-Dose Supplements: Taking supplements containing large amounts of folic acid, especially more than the Tolerable Upper Intake Level (UL) of 1,000 mcg per day for adults.
Fortified Foods: Consuming a diet rich in fortified cereals, breads, pasta, and other products, which contain added folic acid. This can combine with supplement intake, leading to a cumulative excess.
Genetic Factors: Some individuals have a genetic variation (MTHFR polymorphism) that affects their ability to metabolize folic acid efficiently, causing it to build up in the blood.
Kidney Disease: Conditions affecting kidney function can impair the body's ability to excrete excess folate.

Common Symptoms of High Folate Intake

While many people with elevated folate experience no symptoms, high doses of folic acid can trigger a variety of side effects, including:

Digestive Issues: Nausea, bloating, loss of appetite, stomach cramps, and loose stools.
Neurological Concerns: Irritability, confusion, sleep problems, and difficulty concentrating.
Other Side Effects: A bitter or unpleasant taste in the mouth and potential allergic reactions like hives and itching in rare cases.

Folic Acid vs. Natural Food Folate


Feature	Folic Acid	Natural Food Folate
Form	Synthetic, oxidized form.	Natural, reduced form (e.g., 5-MTHF).
Metabolism	Requires conversion by the enzyme DHFR, which can become saturated at high doses, leading to unmetabolized folic acid (UMFA).	Directly converted to its active form (5-MTHF) and is highly bioavailable.
Absorption	Very stable and easily absorbed by the body.	Can be less stable and is more easily destroyed by heat during cooking.
Risk Profile	High intake poses risks, particularly masking B12 deficiency and potential cancer links in some studies.	Very low risk of toxicity from food sources, as the body processes and excretes excess easily.
Tolerable Upper Limit	Has a UL of 1,000 mcg/day for adults due to masking B12 deficiency.	No established UL, as toxicity is not a recognized risk from food sources.

The Connection to Cancer and Cognitive Decline

Research suggests a complex and sometimes conflicting relationship between high folate and health outcomes like cancer and cognitive function. Some studies indicate that while adequate folate levels may be protective against certain cancers, very high levels of folic acid could promote the growth of existing pre-cancerous or cancerous cells. This effect appears to depend on the timing and dosage, with some older studies suggesting higher risks of colorectal and prostate cancer recurrence in individuals supplementing with excessive doses. For older adults with low B12, high folate levels have been associated with accelerated cognitive decline. More research is needed to fully understand these long-term effects.

Conclusion

While a sufficient intake of folate is crucial for overall health and preventing birth defects, more is not always better when it comes to the synthetic version, folic acid. Excessive levels can have serious and subtle consequences, most notably masking a critical vitamin B12 deficiency that can result in irreversible nerve damage. Causes of high folate typically stem from over-supplementation or a combination of supplements and fortified foods. To maintain optimal health, it is wise to prioritize natural folate from a balanced diet and consult with a healthcare provider before taking high-dose supplements. A comprehensive blood panel testing for folate, B12, and homocysteine levels can provide clarity on your nutritional status. NIH Office of Dietary Supplements Fact Sheet on Folate

Frequently Asked Questions

Folate is the naturally occurring form of vitamin B9 found in foods. Folic acid is the synthetic, man-made version used in supplements and added to fortified foods like cereal and pasta.

High folate levels primarily cause nerve damage indirectly by masking a coexisting vitamin B12 deficiency. By hiding the anemia, it delays the diagnosis and treatment of the B12 issue, allowing neurological damage to progress silently.

For adults, the Tolerable Upper Intake Level (UL) for synthetic folic acid is 1,000 mcg (1 mg) per day. This limit is primarily set to prevent the masking of a vitamin B12 deficiency and does not apply to natural food folate.

While many people have no symptoms, initial signs can include gastrointestinal distress like nausea and bloating. Neurological symptoms such as irritability, confusion, and sleep problems may also occur.

To lower elevated folate levels, you should review your intake from all sources, including supplements and fortified foods. Reducing or stopping folic acid supplements under medical supervision is often the primary step. Prioritizing natural folate-rich foods is a safer approach.

Yes. Older adults, who are more susceptible to poor B12 absorption, and individuals with genetic factors like an MTHFR variant that impairs folic acid metabolism are at higher risk.

High folate from natural food sources is not considered a risk, as the body processes and excretes it differently than synthetic folic acid. The concern over excessive intake is linked to folic acid from supplements and fortified foods.

Food fortification with folic acid was mandated in some countries to help prevent neural tube defects in newborns. For most of the population, moderate intake from fortification is safe and beneficial, but high overall intake from multiple sources can become an issue for certain individuals.