What causes impaired absorption in folic acid deficiency?

Updated: Sep 14, 2018
  • Author: Katherine Coffey-Vega, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

The limiting factor in folate absorption is its transport across the intestinal wall. Folate transport across the gut wall mainly is carrier mediated, saturable, substrate specific, pH dependent (optimal at low pH), sodium dependent, and susceptible to metabolic inhibitors. Passive, diffusional absorption also occurs, to a minor degree. With this in mind, a decreased absorptive area due to small bowel resection or mesenteric vascular insufficiency would decrease folate absorption.

Celiac disease and tropical sprue cause villous atrophy. The process of aging causes shorter and broader villi in 25% of the elderly population. Achlorhydria leads to elevation of gastric pH above the optimal level (ie, pH of 5) for folate absorption. Anticonvulsant drugs, such as Dilantin, interfere with mucosal conjugase, hence impairing folate absorption. Zinc deficiency also decreases folate absorption because zinc is required to activate mucosal conjugase. Bacterial overgrowth in blind loops, stricture formation, or jejunal diverticula likewise would decrease folate absorption.


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