Time-of-day difference in iron supplementation in iron-deficient pregnant model mice

During pregnancy, iron supplementation is commonly recommended once daily, partly because hepatic hepcidin secretion following iron intake suppresses subsequent iron absorption. However, the optimal timing of iron administration during maternal iron deficiency remains unknown. We established a pregnant mouse model of iron deficiency and compared the effects of iron (FeSO₄, 1 mg/kg) supplementation at the beginning (ZT12) and end (ZT0) of the daily active phase of pregnant mice on maternal, placental, and fetal outcomes. Supplementation at ZT12 significantly enhanced placental iron transport-related mRNA expression, increased placental iron storage, and improved fetal weight and survival compared to the iron-deficient or iron supplementation at ZT0. Both iron deficiency and iron supplementation markedly altered the maternal gut microbial composition; in particular, Proteobacteria, which are widely reported to be associated with intestinal inflammatory status, were significantly elevated in mice supplemented at ZT0. The rhythmicity of key placental iron transport genes expression was altered by iron deficiency or Clock mutations. This study proposes a chrono-nutritional strategy to maximize iron transport and fetal benefits.