Research published ahead of print in the Archives of Disease in Childhood reports that blood lead levels that are significantly inferior to the accepted "safe" threshold harm young children's intellectual and emotional development.

The existing safety threshold above which blood lead levels give cause for concern is 10 µg/dl. This was dictated by the US Centers for Disease Control in 1991. But there is growing concern that this may be too elevated.

Researchers from the University of Bristol took blood samples from 582 children. They were all part of the Avon Longitudinal Study of Parents and Children (ALSPAC). They evaluated the blood lead levels at thirty months of age.

They later assessed these children's academic performance and behavioral patterns when they turned seven to eight years old. They could obtain complete information for 488 of the children.

They considered factors that could possibly influence the results. Findings suggested an apparent connection between blood lead levels in early childhood and academic performance and behavior by the ages of seven and eight.

Results showed that the higher the level of lead in the blood at the age of thirty months, the poorer were the levels in reading, writing, and spelling grades on the Standard Assessment Tests (SATS). In addition, there were greater chances of antisocial behavior.

No clear effect on intellectual capacity or behavior was evident with lead levels up 5 µg/dl.

Lead levels of between 5 and 10 µg/dl were linked with notably inferior scores for reading (49 percent lower) and writing (51 percent lower). A doubling in lead level from 5 to 10 µg/dl was associated with a 0.3 point drop in SAT scores.

Children with lead levels superior to 10 µg/dl were about three times as likely to show antisocial behavior patterns and be hyperactive as children whose blood levels were between 0 and 2 µg/dl.

Researchers emphasize that the impact is considerable at a population level, although the effect sizes were small.

"The effects of lead exposure are greater when children are very young," explain the authors, "because the toxin is readily absorbed into their developing bodies, and their tissues are especially vulnerable to damage."

In addition, children process lead differently from adults. They absorb up to 50 percent of the lead content they take in. Adults absorb around 15 percent.

Once absorbed, most lead is stored in the bones. It can remain there for up to thirty years, and irreversibly damage the central nervous system.

The authors write: "The clinical importance of these findings is that exposure to lead may interact with other environmental factors associated with educational disadvantage to have a cumulative long term impact."

They demand that the current threshold of 10 µg/dl be halved to 5 µg/dl.

An estimate from the World Health Organization considers globally that half of all children living in cities and towns under the age of five have blood lead levels above 10 µg/dl.

"Effects of early childhood lead exposure on academic performance and behaviour of school age children"
K Chandramouli, C D Steer, M Ellis, A M Emond
Online First Arch Dis Child 2009;
doi: 10.1136/adc.2008.149955
Archives of Disease in Childhood

Stephanie Brunner (B.A.)

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