IQ Linked to Lead Exposure

Summary
Lead is known to affect the human nervous system. The guidelines for safety levels for lead in blood have been revised in the past based on the findings of research studies. The current study was based on a group of participants whose blood concentration of lead was documented from the birth. This study showed that the IQ levels in adults were inversely related to blood levels of lead in childhood. The study also highlighted the need for strategies to limit the exposure to lead even below the levels currently considered safe.

Introduction
The metal lead is a known health hazard. The effects of lead toxicity on the brain have been documented previously, both in children and adults. A long-term follow-up study was initiated in Boston in the 1970s and 1980s, to study the relation between lead and the brain. The long-term follow-up study enrolled newborns and followed their development subsequently up to 10 years. The current study was aimed at finding the association between adult intellectual level and early-life exposure to lead in the same group. This study also tried to find the critical period during child development when lead levels in blood can predict future intellectual performance.

Methodology
* During August 1979 to April 1981, 249 infants born at the Brigham and Women’s Hospital in Boston were recruited for previous study.
* Lead levels in the blood from the umbilical cord were recorded. The blood lead concentration was again measured at 6, 12, 18, 24, and 57 months and 10 years after birth. The medical records and developmental details were available for these participants.
* From the original group, 43 participants underwent neuropsychological examination and blood tests again in January 2009.
* The parents of the participants also answered a questionnaire that provided information about education, employment, history of arrests, concurrent medications, etc.

Results
* The mean blood lead concentration was the lowest at the age of 10 years and was maximal at the age of 2 years.
* The mean IQ in the group was approximately 122 at the age of 29 years.
* Adult IQ was strongly correlated with IQ scores of the participants at the ages of 57 months (or almost five years) and 10 years. A participant’s early childhood IQ was likely to be high if the IQ of the mother was also high.
* IQs in adults were inversely associated with blood lead concentrations in childhood.

Next steps/Shortcomings
The study used a small number of participants from a geographical area. Hence, it is difficult to generalize the findings. This study showed that participants’ IQs were strongly correlated to maternal IQ. Mothers with high IQs might have been intentionally careful in minimizing environmental lead exposure in their children. More research might explain these things better.

Conclusion
This study found that IQ in adulthood is inversely related to blood level of lead measured in childhood. This indicates that the adverse effects of early-life lead exposure could be persistent. The study showed that lead concentrations during the school age years are related to the IQ in adulthood. This may represent a time period of child development when the brain is highly susceptible to environmental lead. It was observed that even in the concentrations considered as safe, lead can negatively affect the brain. “Given the small sample size, however, the potentially confounding effects of maternal IQ cannot be excluded and should be evaluated in a larger study.”

For More Information:
Low-Level Environmental Lead Exposure in Childhood and Adult Intellectual Function: A Follow-Up Study
Publication Journal: Environmental Health, March 2011
By Maitreyi Mazumdar; David Bellinger; Children’s Hospital Boston, Boston, Massachusetts

*FYI Living Lab Reports Are Summaries of the Original Research.
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