Sex differences in iron status during infancy.
BACKGROUND
It is commonly assumed that there is no difference in iron status between male and female infants, despite a lack of studies addressing this question.


OBJECTIVE
To study sex differences in different measures of iron status in infants.


METHODS
At 4 months of age, 263 term, breastfed infants (121 Swedish and 142 Honduran) were randomized to receive iron supplements or placebo until 9 months of age. Blood samples at 4, 6, and 9 months of age were analyzed for hemoglobin (Hb), mean cell volume (MCV), zinc protoporphyrin (ZPP), plasma ferritin, and transferrin receptors (TfR).


RESULTS
At 4, 6, and 9 months, boys had significantly lower Hb, MCV, and ferritin and higher ZPP and TfR than girls. At 9 months, boys had a 10-fold higher risk of being classified as having iron deficiency anemia. The differences at 9 months in MCV (71.6 vs 75.1 fL) and ZPP (59 vs 49 micro mol/mol heme) remained significant after controlling for iron supplementation, site, growth variables, and other possible confounders. For ferritin, there was a remaining sex difference at 9 months among Swedish (29 vs 53 micro g/L) but not Honduran infants. For Hb and TfR, sex differences at 9 months were larger in unsupplemented infants, especially in those with a birth weight of <3500 g.


CONCLUSIONS
There are substantial sex differences in Hb and other indicators of iron status during infancy. Some of these may be genetically determined, whereas others seem to reflect an increased incidence of true iron deficiency in boys.
Domellöf
Magnus
M
Department of Clinical Sciences, Pediatrics, Umeå University, Umeå, Sweden.
Lönnerdal
Bo
B
Dewey
Kathryn G
KG
Cohen
Roberta J
RJ
Rivera
L Landa
LL
Hernell
Olle
O
D018798:Anemia, Iron-Deficiency / Q000517:prevention & control*; D001942:Breast Feeding; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006721:Honduras; D006801:Humans; D007223:Infant; D007501:Iron / Q000008:administration & dosage* / Q000097:blood*; D008297:Male; D012737:Sex Factors; D013548:Sweden
D006454:Hemoglobins; D007501:Iron