Circulating IGF-1 may mediate improvements in haemoglobin associated with vitamin A status during pregnancy in rural Nepalese women

Pregnancy exacerbates vitamin A (VA) deficiency and anaemia among women in developing countries. Improving circulating haemoglobin (Hb) requires erythrocyte production and availability of iron. Insulin-like growth factor-1 (IGF-1) functions in erythropoiesis, but its association with VA status and pregnancy-associated anaemia has not been studied. The aim of this study was to examine the relationship between serum retinol, IGF-1, and Hb among pregnant women in extant samples collected during a placebo-controlled trial of VA and beta-carotene (BC) supplementation in rural Nepal conducted from 1994 to 1997. Mid-pregnancy serum IGF-1 was measured in serum from n=589 randomly selected women of n=1186 in whom anthropometric, VA (retinol) and iron (Hb, erythrocyte zinc protoporphyrin (ZP), and ferritin) status data were available. Associations of IGF-1 with retinol, Hb or anaemia, and iron status were determined using multiple linear and logistic regression. Path analysis was used to explore the role of IGF-1 as a mediator between retinol and Hb, accounting for iron status. A 2.6 g/L increase in IGF-1 was observed per 0.1 mol/L increment in retinol (p<0.0001). Hb increased with each quartile of IGF-1, and odds of anaemia declined 68.8% from the 1st to 4th quartile. Improved iron status indicators explained only 29.1% of the association between IGF-1 and Hb, while IGF-1 explained 25.6% of the association between retinol and Hb. Increasing IGF-1 was likely one mechanism by which retinol improved circulating Hb in pregnant women of rural Nepal, although IGF-1 worked primarily through pathways independent of improved iron status indicators, perhaps by stimulating erythrocyte production.