Effect of ascorbic acid intake on nonheme-iron absorption from a complete diet.
BACKGROUND
Ascorbic acid has a pronounced enhancing effect on the absorption of dietary nonheme iron when assessed by feeding single meals to fasting subjects. This contrasts with the negligible effect on iron balance of long-term supplementation with vitamin C.


OBJECTIVE
Our goal was to examine the effect of vitamin C on nonheme-iron absorption from a complete diet rather than from single meals.


METHODS
Iron absorption from a complete diet was measured during 3 separate dietary periods in 12 subjects by having the subjects ingest a labeled wheat roll with every meal for 5 d. The diet was freely chosen for the first dietary period and was then altered to maximally decrease or increase the dietary intake of vitamin C during the second and third periods.


RESULTS
There was no significant difference in mean iron absorption among the 3 dietary periods despite a range of mean daily intakes of dietary vitamin C of 51-247 mg/d. When absorption values were adjusted for differences in iron status and the 3 absorption periods were pooled, multiple regression analysis indicated that iron absorption correlated negatively with dietary phosphate (P = 0.0005) and positively with ascorbic acid (P = 0.0069) and animal tissue (P = 0.0285).


CONCLUSIONS
The facilitating effect of vitamin C on iron absorption from a complete diet is far less pronounced than that from single meals. These findings may explain why several prior studies did not show a significant effect on iron status of prolonged supplementation with vitamin C.
Cook
J D
JD
Department of Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA. jcook1@kumc.edu
Reddy
M B
MB
D000328:Adult; D001205:Ascorbic Acid / Q000008:administration & dosage* / Q000494:pharmacology; D004032:Diet; D019587:Dietary Supplements; D005215:Fasting; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D007501:Iron / Q000097:blood; D019266:Iron, Dietary / Q000008:administration & dosage / Q000493:pharmacokinetics*; D007553:Isotope Labeling; D008297:Male; D008460:Meat; D010758:Phosphorus / Q000009:adverse effects
D019266:Iron, Dietary; D010758:Phosphorus; D007501:Iron; D001205:Ascorbic Acid