Periconceptional maternal diet quality influences blood heavy metal concentrations and their effect on low birth weight: the Japan Environment and Children’s Study

[Display omitted] •Prenatal exposure to heavy metals is associated with a higher risk of low birth weight.•A well-balanced periconceptional maternal diet carries a lower risk of low birth weight.•High maternal diet quality is associated with high blood mercury and low lead and cadmium levels.•The effect of prenatal lead exposure on low birth weight is attenuated by a high-quality maternal diet. Both poor maternal nutrition and toxic heavy metal exposure influence foetal growth and development. However, whether consumption of a variety of healthy foods modifies the association between prenatal heavy metal exposure and foetal growth is unknown. We examined whether long-term maternal diet quality in periconception modifies the associations between maternal circulating concentrations of heavy metals and foetal growth. Data of 72,317 Japanese women who delivered singleton infants was extracted from the Japan Environment and Children’s Study. Maternal diet over a 1-year before the first trimester of pregnancy was assessed using a validated food frequency questionnaire, and overall diet quality was determined using the balanced diet score based on the Japanese Food Guide Spinning Top. Maternal whole-blood concentrations of mercury (Hg), lead (Pb) and cadmium (Cd) were measured during the second/third trimester of pregnancy. Bayesian inference of multiple linear regression analysis was performed to evaluate the relationships between maternal diet quality and the blood concentrations of heavy metals; Bayesian logistic regression was used to analyse the risk of low birth weight (LBW;