Telomere length in newborns is associated with exposure to low levels of air pollution during pregnancy

• Air pollution during pregnancy associated with telomere length (TL) in newborns. • Second trimester air pollution positively associated with umbilical cord blood TL. • Third trimester air pollution inversely associated with umbilical cord blood TL. • Air pollution at home and work show similar association with umbilical cord blood TL. • No association between air pollution and TL in placenta or maternal blood. Telomere length (TL) is a biomarker of biological aging that may be affected by prenatal exposure to air pollution. The aim of this study was to assess the association between prenatal exposure to air pollution and TL in maternal blood cells (leukocytes), placenta and umbilical cord blood cells, sampled immediately after birth in 296 Danish mother-child pairs from a birth cohort. Exposure data was obtained using the high-resolution and spatial–temporal air pollution modeling system DEHM-UBM-AirGIS for PM 2.5 , PM 10 , SO 2 , NH 4 + , black carbon (BC), organic carbon (OC), CO, O 3 , NO 2 , and NO x at residential and occupational addresses of the participating women for the full duration of the pregnancy. The association between prenatal exposure to air pollutants and TL was investigated using distributed lag models. There were significant and positive associations between TL in umbilical cord blood cells and prenatal exposure to BC, OC, NO 2 , NO x , CO, and O 3 during the second trimester. TL in umbilical cord blood was significantly and inversely associated with prenatal exposure to PM 2.5 , BC, OC, SO 2 , NH 4 + , CO and NO 2 during the third trimester. There were similar inverse associations between TL from umbilical cord blood cells and air pollution exposure at the residential and occupational addresses. There were weaker or no associations between air pollution exposure and TL in placenta tissue and maternal blood cells. In conclusion, both the second and third trimesters of pregnancy are shown to be sensitive windows of exposure to air pollution affecting fetal TL.