Effects of zinc and manganese across different pregnancy trimesters on low birth weight risk: a nested case–control study

Zn and Mn are essential nutrients for fetal growth and development. Since deficiency of maternal nutrition may lead to preventable adverse pregnancy outcomes, we aimed to examine the association of maternal dietary Zn and Mn levels with low birth weight (LBW). A nested case–control study was conducted in 605 cases and 7497 controls in Lanzhou, China. Eligible participants reported on their diet and characteristics during pregnancy. The relationship between dietary Zn and Mn intake and the risk of LBW was analysed by unconditioned logistic regression and multivariate adjusted restricted cubic spline model. The receiver operating characteristic curve was used to determine the optimal cut-off values of Zn and Mn. The dietary intake below the cut-off value was defined as the low-level group, and greater than or equal to the cut-off value was defined as the high-level group. Low dietary Zn (<5·05 mg/d before pregnancy and <7·36 mg/d during pregnancy) and Mn (<2·66 mg/d before pregnancy and <3·41 mg/d during pregnancy) intake was associated with increased risk of LBW and some subtypes. Both Zn and Mn have a nonlinear relationship with the risk of LBW (<i>P</i> < 0·001). In addition, there was a synergistic effect of low Zn and low Mn intake on LBW risk. There were separate and interaction effects of Zn and Mn on the occurrence of LBW. An appropriate range of Zn and Mn intake may be beneficial to reduce the risk of LBW.