Prenatal, Concurrent, and Sex-Specific Associations between Blood Lead Concentrations and IQ in Preschool Canadian Children (Lay summary)

Desrochers-Couture M, Oulhote Y, Arbuckle TE, Fraser WD, Séguin JR, Ouellet E, Forget-Dubois N, Ayotte P, Boivin M, Lanphear BP, Muckle G. Environment International. 2018 Nov 1. pii: S0160-4120(18)31251-0. doi: 10.1016/j.envint.2018.10.043.

Lead is a toxic metal that can be present at low levels in food, drinking water, air, dust, soil, and personal care products. Blood lead levels have been declining over the past 25 years. This is primarily due to legislation by Health Canada, Environment Canada, and other Canadian regulatory agencies to reduce lead in gasoline and house paints and the use of lead-soldered food cans.

Elevated lead exposure during early childhood (> 5 µg/dL) can adversely affect a child’s intellectual (e.g., IQ) and behavioural development. However, less is known about potential associations between prenatal lead exposure and child IQ at the low levels typically experienced by the Canadian population.

In this MIREC study, lead was measured in maternal blood samples collected in the 1st and 3rd trimesters of pregnancy, as well as in umbilical cord blood and child blood (ages 3-4 years). The child’s IQ was measured at age 3 or 4 years. The tests administered to the children measured their verbal IQ (measures acquired knowledge, verbal reasoning and comprehension, and attention to verbal stimuli), performance IQ (measures fluid reasoning, spatial processing, attentiveness to detail and visuo-motor integration), general language abilities, and full-scale IQ (general intellectual abilities).

Data were available for 609 mothers and their children. During pregnancy, the average maternal blood lead concentration was 0.6 µg/dL. The average cord blood lead concentration was 0.8 µg/dL and the average blood lead concentration in the children was 0.7 µg/dL. No association was observed between cord blood lead concentrations and full-scale IQ. However, as cord blood lead concentrations increased, performance IQ in boys, but not in girls, decreased. No associations were found between IQ scores and prenatal maternal blood or child blood lead concentrations.

In conclusion, this study did not find any association between maternal or child blood lead levels and child IQ scores at the current low levels experienced by MIREC families. The results did suggest, however, that boys may be more susceptible to the effects of early life exposure to lead than girls. This study is the first to report that cord lead concentrations below 5 μg/dL are associated with lower performance IQ in preschool boys. It will be interesting to see whether other studies will find similar results and therefore confirm this result.

This work was led by a graduate student at Laval University, in collaboration with scientists from Health Canada, Simon Fraser, Harvard and Laval Universities, Universities of Montreal and Sherbrooke, CHU Sainte-Justine Research Center, and Institut national de santé publique du Québec.

For more information on lead, see https://www.canada.ca/en/health-canada/services/environmental-workplace-health/environmental-contaminants/lead/lead-information-package-some-commonly-asked-questions-about-lead-human-health.html.