Exposure to small quantities of lead in early childhood stunts neurological development and lowers classroom performance of children regardless of their socioeconomic level, a study reported in the Oct. 22 issue of the New England Journal of Medicine suggests.
The findings of the study, which unlike many previous efforts focused on middle-class rather than poor families, support those of earlier reports demonstrating how lead exposure can impair intelligence.
The researchers studied 494 children from a small lead-mining town in Australia over a three-year period. Controlling for parental levels of education, maternal age at delivery, and home environment, among other factors, the researchers found that I.Q.-test scores were 5 percent lower in children under age 7 who had been exposed during infancy to low levels of lead.
One-third of the children's blood-lead levels exceeded 25 micrograms per deciliter, a level that is known to affect I.Q. scores.
Last year, the U.S. Centers for Disease Control lowered the level at which children are considered at risk of becoming lead poisoned, from 25 micrograms per deciliter of blood to 10 micrograms per deciliter, because of numerous reports linking lead contamination to lower intelligence-test scores. Young children who are exposed to lead between 15 months and 4 years of age are at the greatest risk, the authors noted.
Biologists recently confirmed what parents have known empirically for years: Children grow in periodic spurts. Researchers have long insisted that an infant's growth is more or less continuous, with sporadic growth bursts along the way.
But a new study conducted by researchers at the Universty of Pennsylvania shows that an infant's growth pattern is better characterized as concentrated 24-hour spurts in growth with no measurable gain in between.
Researchers studied 31 white infants during their first 21 months of life. The infants were divided into three groups and measured daily, twice a week, or weekly, laying them against a headboard to reduce movement.
The growth spurts of children who were measured weekly were from 0.5 to 2.5 centimeters (approximately one-fifth of an inch to one inch), punctuated by periods of no growth lasting from seven to 63 days. The children measured daily had spurts of 0.8 to 1.65 centimeters (approximately one-third to two-thirds of an inch), separated by periods of no growth ranging from two to 28 days.
The explanation is not that there is a change in the speed at which
an infant grows, but that growth is either present or not, said Dr.
Michelle Lampl, a physician and anthropologist at the University of
Pennsylvania and a co-author of the study.--J.P.