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Brian S. Schwartz, M.D., M.S. New research by NIEHS-supported investigators at the Johns Hopkins Bloomberg School of Public Health suggests that the "normal" cognitive decline experienced as we age may be related to our recent and life-time exposure to lead. In three separate independent epidemiologic studies, bone lead content was associated with poorer measures of cognitive function. The three studies used different cohorts of people. One study included 1,109 former U.S. employees of a tetraethyl lead manufacturing facility. Tetraethyl lead was used in gasoline in the U.S. from the 1920’s to the 1970’s. It is still used in some foreign countries. Another study was based on 803 current and former workers in a Korean inorganic lead industrial setting. Participants in the third study were 1,140 Baltimore residents, aged 50-70, with environmental lead exposure. Bone lead was measured using X-ray fluorescence of the tibia. The researchers noted a persistent and consistent association of poorer cognitive function with higher tibia lead levels in all three studies. MRI brain scans in the U.S. worker cohort also showed lower brain volumes in people with high tibia lead. The research also indicates that the greater the bone lead content, the sooner the cognitive decline starts. Added to the knowledge that exposure to lead lowers the peak IQ a person reaches, these studies show that lead exposure is a life-long issue. The authors also point out that the current occupational safety standards for lead workers are inadequate to protect them. They believe that blood lead levels in adults should be kept below 20 micrograms per deciliter of blood and tibia lead should be kept below 15 micrograms per gram to prevent cognitive function loss. Citation: Stewart WF, Schwartz BS. Effects of lead on the adult brain: a 15-year exploration. Am J Ind Med. 2007 Oct;50(10):729-39.
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