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Lead effects show in child's balance.

Lead effects show in child's balance

First it was diminished IQ. Then it was delayed motor development, hearing difficulty and impaired memory. Now, another subtle health effect has been identified in children carying a low-level body burden of lead: They have trouble balancing.

Since 1980, researchers at the University of Cincinnati School of Medicine have been studying lead's effects on inner-city children (SN: 9/13/86, p.164)-those most likely to experience toxic exposures. Besides evaluating motor skills and mental abilities, this project records blood-lead levels every three months for 6.5 years, starting at birth.

Two observations tipped the researchers off to lead's effect on balance. First, the older children, aged 4 or 5, often clung to stair railings with both hands and climbed slowly up or down. Second, in general balance tests--like walking on a beam -- many consistently performed below levels normal for their age.

Adding to their suspicions were studies by others linking lead exposures to problems with nerve conduction--the relay of messages to and from the brain. Since balance relies on information relayed by sensory nerves, they decided to evaluate their 6-year-olds using a "postural-sway force platform." To plot swaying over time, sensors embedded in the metal platform measure force and twisting motion in three directions: side-to-side, front-to-back and up-down.

Each child participated in four 30-second tests: standing directly on the platform with eyes open, standing on the platform with eyes closed, standing atop 3 inches of foam with eyes open and standing atop the foam with eyes closed. Each test forces reliance on a different sensory system important to balance: vision, receptors on the feet, input from joints and stimuli from the inner ear.

Data on the first 63 of almost 300 children to be tested suggest the joint-based and inner-ear balancing systems are most sensitive to lead. In the tests that forced reliance on these systems, for every 1-microgram-per-deciliter ([mu]g/dl) increase in a child's maximum blood-lead level, the total area of sway increased by an average of roughly 2.8 square centimeters, reports Amit Bhattacharya, who directed the study. Those maximum blood-lead levels tend to peak at about age 2, when children typically explore their environment "hand to mouth" and are most likely to ingest lead-tainted debris and dirt.

Bhattacharya says it appears the observed dose-related impairments result from the fact that lead exposure "peaks precisely at the age when a child's neuromuscular system -- important to balance--is maturing." He presented the findings this month at a National Institute of Environmental Health Sciences conference in Research Triangle Park, N.C.

At the time these children were tested, their mean blood-lead level was just 17.9 [mu]g/dl--well below the 25 [mu]g/dl that the Centers of Disease Control has labeled "excessive" (SN: 11/22/86, p.333). Bhattacharya suggests a refined version of the postural-sway testing might one day be used to screen other such children with subclinical lead exposures, in order to identify those predisposed toward clumsiness. "Balance can be improved," he notes, if children receive special training at an early age.

J. Julian Chisolm, a pediatrician at Johns Hopkins University in Baltimore, thinks the test's biggest impact could be in directing new lines of research. Studies of lead have tended to focus on its central nervous system effects. "These data," he says, "suggest the peripheral nervous system is affected as well."

But because the test "has the potential to provide a more objective measurement of lead impairment," says J. Routt Reigart, at the Medical University of South Carolina in Charleston, physicians might be able to combine it with blood testing to help establish which lead-exposed children have suffered actual neurological impairment.
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Author:Raloff, Janet
Publication:Science News
Date:Jan 28, 1989
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