Which site is the primary site for folate absorption?

• A. Duodenum
• B. Jejunum
• C. Ileum
• D. Duodenum and proximal jejunum

Answer: (D)

Folate absorption happens mostly in the proximal part of the small intestine, with the duodenum and the upper portion of the jejunum doing the bulk of the work. Dietary folate is usually polyglutamated and must be deconjugated by brush-border enzymes to the monoglutamate form before it can enter enterocytes. The transporter that brings folate into cells, the proton-coupled folate transporter, is most active in the upper small intestine where pH is favorable, so the duodenum and proximal jejunum together absorb most of what is ingested. The ileum plays a smaller role in folate uptake and is more critical for vitamin B12 absorption, reinforcing that the front part of the small intestine is the main site for folate.