Blood lead and IQ in older children.In their article about blood lead and IQ in older children, Chen et al. (2005) made the very important observation that IQ (intelligence quotient intelligence quotient n. Abbr. IQ An index of measured intelligence expressed as the ratio of tested mental age to chronological age, multiplied by 100. ) in older children correlates better with their current blood lead level than with levels determined at 2 years of age. This observation has enormous public health implications in terms of defining who is at risk of cognitive decrement To subtract a number from another number. Decrementing a counter means to subtract 1 or some other number from its current value. upon exposure to lead, and challenges the widely held assumption that the effects of lead on neurobehavioral function are exclusively developmental. My colleagues and I (Carpenter et al. 2002) previously studied the effects of gestational and lactational exposure of rats to lead with measurement of long-term potentiation in hippocampal hip·po·cam·pus n. pl. hip·po·cam·pi A ridge in the floor of each lateral ventricle of the brain that consists mainly of gray matter and has a central role in memory processes. brain slices. Long-term potentiation is an electrophysiological measure of synaptic plasticity synaptic plasticity Physiology Malleability present in synapses in various forms–eg, presynaptic inhibition, homosynaptic depression, presynaptic facilitation and modulation of transmitter release by tonic depolarization of sensory neuron. that is widely viewed as being at least one component of learning and memory, and it is reduced upon in vivo in vivo /in vi·vo/ (ve´vo) [L.] within the living body. in vi·vo adj. Within a living organism. in vivo adv. lead exposure. To our surprise we also found that acute perfusion of low concentrations of lead onto brain slices from control animals resulted in reduction of long-term potentiation, suggesting that the effect is more pharmacologic than developmental. The results of Chen et al. (2005) in humans and our studies in rats suggest that lead causes both developmental and pharmacologic impairment of cognitive function cognitive function Neurology Any mental process that involves symbolic operations–eg, perception, memory, creation of imagery, and thinking; CFs encompasses awareness and capacity for judgment . If this is true, then steps should be taken to prevent exposure to lead and to reduce lead levels in individuals of any age, not just young children. The author declares he has no competing financial interests. Editor's note: In accordance with journal policy, Chen et al. were asked whether they wanted to respond to this letter, but they chose not to do so. REFERENCES Carpenter DO, Hussain RJ, Berger DF, Lombardo JP, Park HY. 2002. Electrophysiologic and behavioral effects of perinatal and acute exposure of rats to lead and polychlorinated biphenyls. Environ Health Perspect 110(suppl 3):377-386. Chen A, Dietrich KN, Ware JH, Radcliffe J, Rogan WJ. 2905. IQ and blood lead from 2 to 7 years of age: are the effects in older children the residual of high blood lead concentrations in 2-year-olds? Environ Health Perspect 113:597-601. David O. Carpenter Institute for Health and the Environment University at Albany Rensselaer, New York Rensselaer is a city in Rensselaer County, New York, U.S., located on the Hudson River, directly opposite Albany. As of the 2000 census, the city population was 7,761; in 1920, it was 10,832. E-mail: carpent@uamail.albany.edu |
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