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'Safe' Blood Lead Levels Can Cause Cognitive Deficits

BALTIMORE (Reuters Health) May 01 - Lead can cause cognitive deficits in children even when blood levels are well below the officially sanctioned 10 g/dL mark, according to study results presented Monday at the Pediatric Academic Societies Annual Meeting in Baltimore.

The concentration for defining lead intoxication has been lowered progressively from 60 g/dL to 10 g/dL over the past three decades, explained Dr. Bruce Lanphear from Children's Hospital Medical Center in Cincinnati, Ohio. But he described the choice of 10 g as arbitrary, saying that it remains unclear whether lower levels are actually harmless.

Dr. Lanphear and his associates measured blood lead levels during the first 5 years of life and IQ at 60 months in 276 children and adjusted their comparisons for factors with a recognized influence on child IQ (sex, birthweight, maternal IQ, in utero tobacco exposure, and so on). Dr. Lanphear reported that the mean blood lead level at 60 months was 6.1 g/dL and the mean IQ was 90.

The mean blood lead level rose from 1.9 g/dL at 6 months of age to peak at 9.3 g/dL at 24 months, when 33.8% of children had levels above the 10 g/dL "safe" cutoff, Dr. Lanphear said.

"There was a consistent inverse association between blood lead level and IQ," Dr. Lanphear noted, "which proved statistically significant beginning at 36 months of age."

Overall, Dr. Lanphear said, there was a 5.7-point drop in IQ for each 10-g/dL increase in blood lead level. But among children with lower lead levels, the effect of rising lead levels was more striking: an 11.5-point drop for those whose levels were initially below 10 g/dL and more than a 15-point drop for children whose lead levels were initially below 5 g/dL.

Moreover, contrary to previous suggestions, concurrent lead levels proved better predictors of cognitive defects than did lead concentrations earlier in childhood, the results indicated.

Dr. Lanphear urged a primary prevention strategy aimed at eliminating lead from housing before children are exposed. "We need to stop using children as biological markers for substandard housing practices," he said, "and to test the safety and efficacy of existing lead hazard controls."