What Stops the Body From Absorbing Folic Acid?

November 14, 2025 •

5 min read

According to the CDC, mandatory folic acid fortification of grain products has significantly reduced deficiency rates in some countries, but many factors can still impede absorption. Understanding what stops the body from absorbing folic acid is crucial for managing health, as a deficiency can lead to megaloblastic anemia and other serious complications.

Quick Summary

This article examines the primary factors inhibiting folic acid absorption, including genetic variants, underlying gastrointestinal diseases, specific medications, and chronic alcohol use. It provides a comprehensive overview of how these diverse elements can lead to folate deficiency and elevated homocysteine levels.

Key Points

Genetic Variants: A polymorphism in the MTHFR gene can hinder the body's conversion of folic acid to its active form, leading to a functional deficiency.
Gastrointestinal Diseases: Conditions like celiac and Crohn's disease can damage the intestinal lining, impairing nutrient absorption, including folic acid.
Medications: Certain drugs, such as methotrexate and some anticonvulsants, act as folate antagonists and interfere with its metabolism or absorption.
Chronic Alcohol Use: Excessive and long-term alcohol consumption disrupts folate absorption, storage, and metabolism, significantly increasing the risk of deficiency.
Vitamin B12 Interaction: A deficiency in vitamin B12 can trap folate in an inactive form, making it unusable by the body despite adequate intake.
Dietary Factors: Inadequate consumption of folate-rich foods and overcooking can reduce dietary intake, as folate is heat-sensitive.
Surgical Procedures: Resection of the small intestine, including some bariatric surgeries, can reduce the area available for absorption.

Genetic Factors and MTHFR Polymorphism

One of the most significant reasons the body may struggle with folic acid is a genetic variant affecting the methylenetetrahydrofolate reductase (MTHFR) gene. This gene provides instructions for making the MTHFR enzyme, which is critical for converting folic acid (the synthetic form) and dietary folate into its active, usable form, 5-MTHF.

The Role of the MTHFR Gene

A common variant, MTHFR C677T, is known to reduce the enzyme's activity. Individuals with this polymorphism may not efficiently convert folate to 5-MTHF, which can lead to higher homocysteine levels and potential health issues. While the CDC notes that even with this variant, the recommended daily dose of folic acid helps prevent neural tube defects, it highlights a key metabolic hurdle for some individuals.

Medical Conditions Causing Malabsorption

Certain medical conditions directly impact the body's ability to absorb folic acid in the small intestine, where most absorption occurs. Damage or inflammation in this area can significantly reduce nutrient uptake.

Intestinal Diseases and Gastric Issues

Celiac Disease: This autoimmune disorder triggers an immune response to gluten that damages the lining of the small intestine, especially the duodenum and jejunum, impairing nutrient absorption. This can cause malabsorption of iron, folate, and other vitamins.
Crohn's Disease and Inflammatory Bowel Disease (IBD): These chronic inflammatory conditions can also cause intestinal damage, leading to impaired absorption of nutrients like folate.
Tropical Sprue: A gastrointestinal illness often seen in tropical regions, tropical sprue can cause malabsorption of several nutrients, including folic acid.
Achlorhydria: Reduced or absent stomach acid can hinder the absorption of some nutrients, though its impact on folate requires further study.
Surgical Resections: Procedures such as bariatric surgery or intestinal resections can reduce the surface area available for absorption, affecting folate uptake.

Medications and Drug Interactions

Several medications can interfere with folate metabolism and absorption, either by blocking absorption or by increasing its breakdown.

Medications That Antagonize Folate

Certain drugs are known as folate antagonists, meaning they directly interfere with the use and metabolism of folic acid. A well-known example is methotrexate, used to treat conditions like severe psoriasis and certain cancers. Other anticonvulsants (phenytoin, phenobarbital) and some antibiotics (trimethoprim) can also interfere with folate.

Lifestyle and Dietary Habits

Poor diet and certain lifestyle choices are common causes of folate deficiency, impacting both intake and absorption.

Chronic Alcohol Consumption

Chronic alcohol use is a major contributor to folate deficiency. Alcohol consumption disrupts folate absorption in the small intestine, impairs its hepatic storage, and increases its excretion through the kidneys.

Cooking and Preparation Methods

Folate is sensitive to heat, and prolonged or overcooking of fruits and vegetables can destroy a significant portion of the naturally occurring vitamin. Steaming or eating raw produce is recommended to preserve folate content.

Vitamin B12 Deficiency

An often-overlooked factor is the interaction with other vitamins. A severe vitamin B12 deficiency can lead to a 'folate trap,' where folate is converted to its inactive form, 5-methyl-THF, but cannot be used for DNA synthesis. This effectively makes usable folate unavailable to the body.

Comparison of Key Inhibitors

This table summarizes the primary factors that impede folic acid absorption, detailing their mechanism and whether they affect intake, absorption, or metabolism.


Factor	Mechanism of Inhibition	Primarily Affects:	Impact on Folic Acid	Resolution/Management
MTHFR Gene Variant	Reduces the activity of the enzyme needed to convert folic acid to its active form (5-MTHF).	Metabolism	Inefficient conversion, leading to functional deficiency.	May require supplements containing 5-MTHF or medical guidance for higher doses.
Celiac Disease	Causes physical damage to the small intestine lining, which is responsible for nutrient absorption.	Absorption	Reduced uptake from all sources, leading to malabsorption.	Strict gluten-free diet to heal the intestine and restore absorption.
Chronic Alcohol Use	Disrupts intestinal absorption, impairs liver storage, and increases urinary excretion of folate.	Absorption, Storage, Excretion	Lower folate levels in serum and tissues.	Decreased alcohol intake or cessation; supplementation may be needed.
Medications (e.g., Methotrexate)	Antagonizes folate metabolism by inhibiting the enzyme dihydrofolate reductase.	Metabolism	Prevents proper utilization of folate, causing functional deficiency.	Careful management and monitoring by a doctor; supplementary folinic acid may be used.
Poor Dietary Habits	Insufficient intake of folate-rich foods; overcooking destroys naturally occurring folate.	Intake	Inadequate supply of the vitamin from dietary sources.	Consuming more folate-rich foods, using low-heat cooking methods.
Vitamin B12 Deficiency	Traps folate in an inactive form, preventing its use by the body's cells.	Metabolism	Creates a functional deficiency where folate is present but unusable.	Treat the underlying B12 deficiency; B12 and folate supplementation together.

Conclusion

Multiple factors, ranging from common genetic variations to specific medical conditions and lifestyle choices, can impede the body's ability to absorb and utilize folic acid effectively. A thorough medical history is essential to pinpoint the root cause of any suspected deficiency. For some, improved dietary habits and cooking methods may be sufficient, while others with malabsorptive disorders, specific gene variants, or chronic illnesses may require targeted supplementation or management of underlying health issues. Consulting a healthcare professional can help develop an appropriate strategy to ensure adequate folate status and prevent associated complications like megaloblastic anemia.

What are folate-rich foods?

Folates are naturally present in many foods. Good sources include leafy green vegetables like spinach, legumes such as black-eyed peas and lentils, citrus fruits, eggs, beef liver, and asparagus. Consuming a balanced diet rich in these foods, along with fortified grains, is key to maintaining adequate intake.

When is it necessary to take folic acid supplements?

Supplementation is recommended for women who are or may become pregnant to reduce the risk of neural tube defects. It is also necessary for individuals with diagnosed deficiencies, malabsorptive disorders, or genetic variants like MTHFR, often requiring medical supervision.

What is the difference between folate and folic acid?

Folate is the naturally occurring form of vitamin B9 found in foods. Folic acid is the synthetic form used in fortified foods and supplements and must be converted by the body into an active form. This conversion can be affected by genetic factors, such as the MTHFR gene variant.

Frequently Asked Questions

No, it does not mean you cannot absorb it at all. However, a common variant can make the enzymatic conversion of folic acid into its active form less efficient. You can still benefit from folic acid, but some people with this variant may be advised to take a supplement with the pre-activated form, 5-MTHF, or a higher dose of folic acid under medical supervision.

Yes. Celiac disease causes damage to the lining of the small intestine, particularly the parts where folic acid is absorbed. This damage impairs the body's ability to absorb nutrients, including folate, from food and supplements.

Several medications are known to interfere with folate metabolism. These include the chemotherapy drug methotrexate, some anticonvulsants (like phenytoin and phenobarbital), and certain antibiotics (such as trimethoprim).

Chronic and excessive alcohol consumption negatively impacts folate levels in several ways. It disrupts absorption in the intestines, reduces liver storage, and increases the rate of excretion by the kidneys. This makes folate deficiency common in individuals with alcohol use disorders.

Folate and B12 work together in the body. A deficiency in vitamin B12 can cause folate to become 'trapped' in an inactive form, preventing its proper use in DNA synthesis. This functional deficiency can lead to health problems even if folate intake is adequate.

Yes, folate is a water-soluble vitamin that is easily destroyed by heat. Overcooking vegetables, especially by boiling, can significantly reduce the amount of folate retained in the food.

Strategies include addressing underlying health conditions like malabsorption disorders, managing alcohol consumption, using supplements containing the active form (5-MTHF) if you have an MTHFR gene variant, and ensuring adequate vitamin B12 levels. Cooking vegetables with minimal heat, like steaming, also helps preserve folate.