Inositol phosphates with different numbers of phosphate groups influence iron absorption in humans.
BACKGROUND
Inositol hexaphosphate (IP(6)) is a well-known inhibitor of iron absorption, whereas the effects of the less-phosphorylated derivatives of IP(6) are less known.


OBJECTIVE
The objective was to investigate the effects of inositol tri-, tetra-, and pentaphosphates (IP(3), IP(4), and IP(5), respectively) on iron absorption in humans.


METHODS
Iron absorption was measured in 5 experiments from single meals by extrinsic labeling with (55)Fe and (59)Fe and determination of whole-body retention and the erythrocyte uptake of isotopes. In experiments 1-3 the meals contained white-wheat rolls to which 10 mg P as IP(5), IP(4), or IP(3), respectively, was added. Inositol 1,2,6-triphosphate [Ins(1,2, 6)P(3)] and a mixture of isomers of IP(4) and IP(5) were studied. White-wheat rolls contained 10 mg P as IP(3) + IP(4) and 2 mg P as IP(5) + IP(6) in experiment 4 and 20 mg P as IP(3) + IP(4) and 3 mg P as IP(5) + IP(6) in experiment 5; inositol phosphates were obtained via fermentation of sodium phytate. Each experiment had 8-11 subjects.


RESULTS
In experiment 1, iron absorption was reduced by 39%, whereas there was no significant effect on iron absorption in experiments 2 and 3. In experiments 4 and 5, iron absorption was reduced by 54% and 64%, respectively, suggesting that IP(3) and IP(4) contributed to the inhibitory effect.


CONCLUSIONS
IP(5) has an inhibitory effect on iron absorption, whereas IP(3) and IP(4) in isolated form have no such effect. IP(3) and IP(4) in processed food contribute to the negative effect on iron absorption, presumably by binding iron between different inositol phosphates. To improve iron absorption from cereals and legumes, degradation of inositol phosphates needs to be to less-phosphorylated inositol phosphates than IP(3).
Sandberg
A S
AS
Department of Food Science, Chalmers University of Technology, University of Göteborg, Sahlgrenska Hospital, Göteborg, Sweden. Ann-Sofie.Sandberg@FSc.Chalmers.se
Brune
M
M
Carlsson
N G
NG
Hallberg
L
L
Skoglund
E
E
Rossander-Hulthén
L
L
D000042:Absorption; D000293:Adolescent; D000328:Adult; D001939:Bread / Q000032:analysis; D002614:Chelating Agents / Q000494:pharmacology*; D005260:Female; D005503:Food Additives / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000494:pharmacology*; D007501:Iron / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D010833:Phytic Acid / Q000494:pharmacology; D012016:Reference Values; D013329:Structure-Activity Relationship
D002614:Chelating Agents; D005503:Food Additives; D007295:Inositol Phosphates; C013571:inositol pentaphosphate; D010833:Phytic Acid; D007501:Iron; C059368:atrinositol