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Even Low Blood Lead Levels Can Have Bad Consequences

Lead levels -- even those not considered to be elevated -- can result in lower IQ and delayed pubertal development in girls.

Since 1990, blood lead concentrations have been considered to be elevated at 10 µg/dL, based on data on cognitive and behavioral development. Two recent articles address the effects of lead levels below this presumably safe threshold.

In a study involving 172 children, researchers measured blood lead levels from age 6 months to 5 years and IQ at ages 3 and 5 years (complete data were obtained for 87% of participants). Children with low birth weight for age, prematurity, speech defects, and prenatal risk factors for low IQ were excluded. Analyses controlled for multiple variables (e.g., maternal IQ, socioeconomic status, and tobacco use during pregnancy). Higher lifetime average lead levels were significantly associated with lower IQ (4.6-point decrease in IQ for each 10-µg increase in lead level). Among 101 children with lead levels at or below 10 µg/dL, the decrease was greater (7.4-point total decrease in IQ in the nonlinear model for lead levels between 1 and 10 µg/dL).

Other researchers examined lead levels and Tanner stages of pubertal development in 2186 girls (age range, 8-18) from a national health and nutrition study. Mean lead level was less than 3 µg/dL. Compared with girls of the same ethnicity who had lead levels of 1 µg/dL, African-American and Mexican-American girls with lead levels of 3 µg/dL had delayed breast and pubic-hair development; the African-American girls also had delays in menarche onset (range of delay, 2-6 months).

Comment: As the editorialists note, chelating treatments for modest lead levels have not been associated with cognitive improvements. Thus, preventing elevations in blood lead levels by decreasing environmental exposure is warranted. Similar measures (e.g., outlawing lead-based house paints and removing lead from gasoline) were successful in lowering children's lead levels to today's levels (median, 2 µg/dL). This success is especially impressive when we consider that elevated blood lead levels were defined as 60 µg/dL in 1960.

— Barbara Geller, MD

Published in Journal Watch Psychiatry May 22, 2003

Citation(s):

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

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Selevan SG et al. Blood lead concentration and delayed puberty in girls. N Engl J Med 2003 Apr 17; 348:1527-36.

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Rogan WJ and Ware JH. Exposure to lead in children -- How low is low enough? N Engl J Med 2003 Apr 17; 348:1515-6.

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