Folic acid is absorbed in which part of the small intestine?

• A. Duodenum
• B. Distal Ileum
• C. Jejunum
• D. Proximal jejunum

Answer: (D)

Folate absorption happens mainly in the proximal portion of the small intestine, where the enterocytes express the proton-coupled folate transporter (PCFT) that takes up monoglutamate folate efficiently at the mildly acidic luminal pH found there. Folates in food are initially in polyglutamate form and must be hydrolyzed to monoglutamate by brush-border enzymes before uptake; this processing and transport are most active in the proximal jejunum. The jejunum in general is the primary site for nutrient absorption, but the proximal portion is where folate absorption is most efficient. The duodenum can contribute to some extent, yet the distal ileum is more important for vitamin B12 absorption, so it’s not the main site for folate. Therefore, the proximal jejunum is the best-match site for folic acid absorption.