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 illions more children and adolescents in the United
States than previously thought endure the detrimental effects
of exposure to lead, according to a new Children's Hospital Medical
Center of Cincinnati study. The study found that lead is toxic
at concentrations in the blood that are much lower than currently
considered acceptable.
 "Cognitive
defects in reading, math, visual construction skills, and short-term
memory, are associated with blood lead concentration considerably
lower than 10 micrograms per deciliter, the level that is considered
'acceptable'," says Bruce P. Lanphear, MD, MPH, the study's
main author. "The data indicate that more than 12.8 million
US children and adolescents who were born between 1972 and 1988,
and who have a blood lead concentration in excess of 2.5 micrograms
per deciliter, are adversely affected by environmental lead exposure."
The researchers
studied 4,853 children who participated in a survey between 1988
and 1994. The children, who ranged from 6 to 16 years old, participated
in the National Health and Nutrition Examination Survey III,
a survey of the health and nutritional status of children and
adults in the United States.
The researchers
found an inverse relation of blood lead concentrations and all
cognitive function scores: reading, math, visual construction
skills and short-term memory. This finding held true for math
and reading scores at blood lead concentrations as low as 2.5
micrograms per deciliter.
Before 1970,
lead poisoning was defined by a blood lead greater than 60 micrograms
per deciliter. Since then, levels considered acceptable declined
several times, before reaching the current 10 micrograms per
deciliter standard. Under this definition of lead toxicity, one
in every 20 children in the United States is adversely affected
by lead exposure. This includes lowered intelligence, behavioral
problems and diminished school performance.
Although blood
lead concentrations below 10 micrograms per deciliter have been
considered "normal" for children, contemporary levels
of childhood lead exposure remain exceedingly high compared with
those of pre-industrial populations. In addition, the lowest
blood lead concentration associated with adverse effects has
not yet been defined.
"Despite
the dramatic decline over the last two decades in the prevalence
of children who have blood lead concentrations above 10 micrograms
per deciliter, these data underscore the increasing importance
of prevention as the consequences of lower blood lead concentrations
are recognized," says Dr. Lanphear, of Cincinnati Children's
division of general and community pediatrics. "The results
of our study argue for a reduction in blood lead levels considered
acceptable to half of what they are now, or even lower. They
also argue for a policy shift toward primary prevention the elimination
of residential lead hazards before children are unduly exposed."
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