When a blood test reveals high levels of serum folate, the result indicates excess Vitamin B9 circulating in the bloodstream. It is important to distinguish between the two primary forms: folate, the naturally occurring form found in foods like leafy greens, and folic acid, the synthetic compound used in supplements and fortified foods. Folic acid is more bioavailable than natural folate, meaning the body absorbs it more readily, and this synthetic form is usually responsible for elevated blood levels. While folate is water-soluble and generally excreted when in excess, a sustained high intake of the synthetic form can overwhelm the body’s metabolic capacity, leading to the measured elevation.
Primary Sources of Excess Folic Acid
The most frequent reason for elevated folic acid levels is excessive external intake from supplements and fortified foods. Many individuals unintentionally consume doses that exceed the recommended daily allowance of 400 micrograms (µg) for adults. This often occurs when a person takes a combination of supplements, such as a daily multivitamin, a B-complex formula, and a separate high-dose folic acid supplement.
Consumption of highly fortified foods is another major contributor to excess intake, even for people who do not take supplements. Since the late 1990s, mandatory fortification programs have required the addition of folic acid to grain products like enriched flours, breads, and breakfast cereals to prevent neural tube defects in newborns. This has increased the baseline intake for the general population.
When high amounts of synthetic folic acid enter the body, the liver’s capacity to convert it into its active form, 5-methyltetrahydrofolate (5-MTHF), can become saturated. This conversion is handled by enzymes, particularly dihydrofolate reductase (DHFR), which has a limited rate of activity. Once the enzyme’s capacity is exceeded, the excess, unconverted compound enters the bloodstream, where it is measured as unmetabolized folic acid (UMFA).
Metabolic Accumulation and Interactions
Accumulation of folic acid in the blood is not always due to over-consumption; it can also indicate an underlying deficiency in another vitamin. The most significant interaction involves Vitamin B12, or cobalamin. A severe B12 deficiency can lead to the “folate trap,” causing folate to accumulate in the serum.
In this trap, the body has plenty of folate, but it remains inactive because B12 is required to complete the final step of the metabolic cycle. B12 transfers a methyl group from 5-MTHF to homocysteine, regenerating active B12 and allowing folate to exit the cycle. Without sufficient B12, the 5-MTHF accumulates, leading to high blood test readings.
Genetic variations can also impair the body’s ability to process folic acid, contributing to its buildup. Individuals with common polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene have a reduced ability to produce the MTHFR enzyme, which creates the active folate, 5-MTHF. This reduced enzymatic activity means the body is less efficient at converting synthetic folic acid into its usable form, leading to higher circulating levels of UMFA. Certain medical conditions, such as liver or kidney impairment, can also interfere with the normal processing and excretion of folate, potentially contributing to elevated levels in the blood.
Symptoms and Potential Health Implications
The primary concern associated with high folic acid levels is not direct toxicity, but the risk of masking a coexisting Vitamin B12 deficiency. High folate intake, whether from supplements or fortification, can correct the megaloblastic anemia associated with B12 deficiency. By correcting the anemia, the high folate removes the early warning signal that prompts investigation.
However, high folate does not prevent the neurological damage caused by the underlying B12 deficiency, which can progress and become irreversible. Symptoms of this hidden B12 deficiency include tingling or numbness in the extremities, difficulty walking, and cognitive issues. An elevated folate result mandates a thorough investigation of B12 status.
The presence of high levels of unmetabolized folic acid (UMFA) itself has raised concerns. Research suggests that high UMFA may alter immune function, potentially reducing the activity of natural killer cells. High intakes of folic acid have also been investigated for potential links to increased risk for certain cancers. Side effects from very high doses can include irritability, insomnia, and gastrointestinal upset.
Next Steps and Medical Consultation
Receiving a blood test result showing high folic acid levels warrants a consultation with a healthcare provider to determine the root cause and ensure B12 status is not compromised. The physician will evaluate your current intake from all sources, including multivitamins, B-complex supplements, and fortified foods. They will likely recommend a temporary reduction or cessation of supplementation to see if levels normalize.
To rule out the “folate trap” and assess for a hidden deficiency, your doctor will perform follow-up blood tests. These tests should include a serum Vitamin B12 level, and sensitive markers of B12 deficiency like methylmalonic acid (MMA) and homocysteine. Elevated MMA and homocysteine levels are stronger indicators of a functional B12 deficiency. Addressing any underlying B12 deficiency must take precedence over managing the high folate.