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Even Low Levels of Lead Can Lower IQ

Clinical Question: Do blood lead levels less than 10 µg per dL (0.5 µmol per L) affect intellectual development in children?

Setting: Population-based

Study Design: Cohort (prospective)

Synopsis: Although we know that lead levels greater than 10 µg per dL are associated with impaired intellectual development, levels less than 10 µg per dL have not been well studied. In this study, the authors identified children at approximately six months of age and followed them until they were five years of age. Lead levels were checked regularly to calculate initial, peak, and average lead levels, and each child's intelligence quotient (IQ) was measured at three and five years of age.

Most of the children were available for follow-up--78 percent at three years and 73 percent at five years. The analysis adjusted for the child's age, home environment, and iron status, as well as the mother's race, income level, prenatal smoking status, IQ, and level of education. The average lead level in this population was 7.4 µg per dL (0.35 µmol per L) and the peak was 11.1 µg per dL (0.55 µmol per L). An increase in the average lifetime lead level of 1 µg per dL (0.05 µmol per L) was associated with a decline in IQ of 0.46 points.

Bottom Line: Even low levels of lead are strongly associated with a decline in intellectual capacity as measured by IQ test results. Efforts to eliminate environmental lead should be redoubled. (Level of Evidence: 1b)

MARK EBELL, M.D., M.S.

STUDY REFERENCE: Canfield RL, et al. Intellectual impairment in children with blood lead concentrations below 10 µg per deciliter. N Engl J Med April 17, 2003;348:1517-26.

Used with permission from Ebell M. Even low lead levels (<10 mcg/dl) can lower IQ. Retrieved June 3, 2003, from: www.InfoPOEMs.com.

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