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Sex differences in iron status during infancy
Magnus Domellöf1, Bo Lönnerdal, Kathryn G Dewey
1Department of Clinical Sciences, Pediatrics, Umeå University, Umeå, Sweden.
Insights
Infant boys show significantly poorer iron status than girls, with higher risks of iron deficiency anemia. These sex differences in iron indicators may be partly genetic or due to increased iron deficiency in boys.
Area of Science:
- Pediatric Nutrition
- Iron Metabolism
- Infant Health
Background:
- Common assumption of no sex difference in infant iron status lacks empirical support.
- Previous research has not adequately addressed sex-based variations in infant iron indicators.
Purpose of the Study:
- To investigate sex differences in multiple iron status measures during infancy.
- To compare iron status indicators between male and female infants from 4 to 9 months of age.
Main Methods:
- Randomized controlled trial involving 263 breastfed infants (Swedish and Honduran).
- Infants received iron supplements or placebo from 4 to 9 months.
- Analysis of hemoglobin (Hb), mean cell volume (MCV), zinc protoporphyrin (ZPP), plasma ferritin, and transferrin receptors (TfR) at 4, 6, and 9 months.
Main Results:
- Boys consistently exhibited lower Hb, MCV, and ferritin, and higher ZPP and TfR compared to girls at all time points.
- At 9 months, boys had a tenfold increased risk of iron deficiency anemia.
- Significant sex differences in MCV and ZPP persisted after adjusting for confounders; ferritin differences remained significant in Swedish infants.
Conclusions:
- Substantial sex differences in iron status indicators are evident during infancy.
- These disparities suggest potential genetic influences and a higher incidence of true iron deficiency in infant boys.
- Findings highlight the need to consider sex in infant iron status assessment and management.
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.