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December 15, 2004
The Effects of Lifetime Exposure to Lead and its
Effect on the Cognition of Children at 11-13 Years |
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Findings of a study indicate that exposure to lead during the first seven years of life
causes cognitive deficits in children. In the research, investigators hoped to
determine if a relationship existed between lead exposure and intelligence at 11 to
13 years of age and to evaluate the consequences to child development.
Methods
Scientists recruited 375 children from Port Pirie, Australia, a lead smelting city
between the years 1979 and 1982. Researchers took blood samples from mothers
at birth (from the umbilical cord), at 6, 15, and 24 months and then annually until the
children reached seven years old. The subjects were followed up again at 11 and 13
years of age.
Investigators utilized the Bayley scales of infant development at age 2, the
McCarthy scales of children's abilities at age 4, and the Wechsler intelligence
scale for children at age 7.
Results
Investigators reported that there was an inverse relationship between pre and
postnatal blood lead concentrations levels. Exposure to lead at ages 15 months to
7 seven years old was highly associated lower IQs at 11 and 13 years. The
average intelligence quotient (IQ) of children decreased by 3 points at age 11 and
13. The average blood lead concentration increased from 0.48 to 0.96 µmol/l—double
the lifetime average. Subjects were less likely to higher than normal blood
concentration levels if they came from a high socioeconomic background, had
high scores on the assessment tests (intelligence scales test), or if their parent
had a high educational background.
Conclusions
Researchers assert that exposure to lead during the first seven years of life is highly
associated with decreases in cognitive abilities. While lead levels in blood reduced
significantly by age three, cognitive deficits persisted. These deficiencies continue
later into life and have negative implications in adulthood. Investigators contend that
the duration, intensity, and timing of exposure to lead, as well as other social and
familial factors, may influence the nature and degree of reversibility.
Lastly, the authors stated that health policy should be created to prevent lead
exposure to persons and that the long term health of children should be considered.
Author and inquiry
Correspondence to: Dr S Tong, Department of Health Services Management and
Public Health, University of New England, Armidale, NSW 2351, Australia.
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