Is folate absorbed in the jejunum or ileum?

January 12, 2026 •

2 min read

Studies have shown that folate absorption occurs primarily in the proximal small intestine, specifically the duodenum and jejunum. This vital nutrient's absorption process relies on specialized transport proteins and a specific pH environment, making it a complex and crucial physiological event.

Quick Summary

Folate absorption happens mainly in the proximal small intestine, primarily the jejunum. The process involves a specific protein carrier, the PCFT, which functions best in the slightly acidic microenvironment of the jejunum.

Key Points

Primary Absorption Site: The vast majority of folate is absorbed in the proximal small intestine, specifically the duodenum and jejunum.
Role of PCFT: The main transport mechanism is the proton-coupled folate transporter (PCFT), which functions best in the slightly acidic environment of the jejunum.
Pre-digestion Requirement: Dietary folates, which are typically polyglutamates, must first be converted into absorbable monoglutamates by an enzyme in the jejunum.
Ileum's Minor Contribution: The ileum plays only a minor, secondary role in folate absorption, and is the primary site for absorbing vitamin B12.
Factors Impacting Absorption: Alcohol, gastrointestinal diseases like celiac, and certain medications can interfere with the body's ability to absorb folate.

Understanding Folate Absorption in the Small Intestine

Folate, or vitamin B9, is a crucial nutrient required for DNA and red blood cell synthesis, as well as for cellular growth and function. Efficient absorption is vital to prevent deficiency-related issues like megaloblastic anemia and birth defects. The small intestine, comprising the duodenum, jejunum, and ileum, is where this absorption takes place. Each section has specialized functions.

The Jejunum and Duodenum: Primary Sites of Absorption

The duodenum and jejunum are the primary sites for folate absorption. A slightly acidic environment in these areas facilitates the uptake process. The main transporter is the Proton-Coupled Folate Transporter (PCFT), which is most effective at the low pH found here.

Dietary folates, typically polyglutamates, must be converted to monoglutamates before absorption. This is done by intestinal glutamate carboxypeptidase II in the jejunum, highlighting its crucial role in processing and uptake.

The Ileum's Secondary Role

The ileum primarily absorbs vitamin B12 and bile acids. Its contribution to folate absorption is significantly less than the jejunum and duodenum, due to differences in transport mechanisms and pH.

Factors Influencing Folate Absorption

Several factors can impact how well folate is absorbed, including:

Chronic alcohol use
Gastrointestinal diseases like Crohn's and celiac disease
Certain medications
Genetic factors such as the MTHFR polymorphism
Overcooking folate-rich foods

Comparison of Nutrient Absorption in the Small Intestine


Feature	Duodenum & Jejunum	Ileum
Primary Function	Major site for digestion and absorption of most nutrients.	Absorption of remaining nutrients, particularly vitamin B12 and bile salts.
Key Absorption Target	Folate, iron, calcium, most vitamins and minerals.	Vitamin B12, bile salts.
Folate Absorption Role	Primary and most efficient site.	Minor role.
Transport Mechanisms	Active transport via carriers like PCFT for folate.	Active transport for B12; bile salt reabsorption.

The Role of Monoglutamates and Polyglutamates

Dietary folate is mostly polyglutamates, but only monoglutamates are absorbed. Intestinal glutamate carboxypeptidase II in the jejunum converts polyglutamates to monoglutamates. The monoglutamate is then transported by PCFT into intestinal cells, converted to active 5-methyl-THF, and released into the bloodstream.

Conclusion: The Jejunum's Central Role in Folate Absorption

Folate is primarily absorbed in the jejunum and duodenum, not the ileum. This process relies on PCFT and the conversion of polyglutamates to monoglutamates in the jejunum. Issues in the proximal small intestine can lead to folate deficiency and health problems.

For more information on folate absorption mechanisms, see the detailed review in PubMed Central(https://pmc.ncbi.nlm.nih.gov/articles/PMC3982215/).

Frequently Asked Questions

Folate absorption is most active in the jejunum due to specialized transporters like PCFT and an optimal pH. The ileum absorbs far less folate and is instead known for absorbing vitamin B12.

The primary transporter responsible for folate absorption in the duodenum and jejunum is the proton-coupled folate transporter (PCFT). It is most efficient in an acidic environment.

Yes, malabsorption can lead to folate deficiency. Conditions such as Crohn's disease or celiac disease, which affect the intestinal lining, can significantly hinder folate absorption.

Excessive alcohol intake can impair the intestinal absorption of folate, contributing to folate deficiency, especially in individuals who also have a poor diet.

Enzymes are essential for preparing folate for absorption. Intestinal glutamate carboxypeptidase II in the jejunum breaks down dietary polyglutamates into absorbable monoglutamates before they are transported into the intestinal cells.

Folic acid is a synthetic form of folate that is easily absorbed by the body. While natural folate is absorbed primarily in the jejunum, folic acid is readily absorbed across different segments of the small intestine.

Poor folate absorption can lead to folate deficiency, resulting in megaloblastic anemia, fatigue, and other symptoms. For pregnant women, it poses a risk of neural tube defects in the fetus.