Lead Poisoning Strikes the Unborn
Buildup in mom's bone transferred to babies
MONDAY, July 1, 2002 (HealthDayNews) -- The sins of the father are borne by the sons, but the poisons of the mother are the children's burden, too.
A new study has found that women whose bones are laced with lead during pregnancy can transfer the toxin to their unborn babies with potentially serious consequences for the child's physical and mental development.
Babies exposed to lead in this way, and through maternal blood, have significantly lower scores on general measures of infant motor and mental ability.
The skeleton normally sequesters the heavy metal, keeping it out of circulation. However, during pregnancy women cannibalize their own bone to help build up the fetal skeleton, setting lead free in the process. Once unlocked, the poison enters the bloodstream and makes its way to the fetus across the umbilical cord.
Lead experts say the findings aren't surprising, and they underscore the importance of reducing exposure to the toxin in young girls.
"These bone stores of lead persist for a very long time," says Dr. Howard Hu, a Harvard University public health expert and a co-author of the study. Whereas a blood lead level reading offers a snapshot of recent exposure, a bone test reflects contact with the metal perhaps decades ago.
The findings also suggest that steps to prevent the release of lead during pregnancy may protect babies. Taking calcium supplements, which shore up the skeleton and slow bone breakdown, is one promising approach, Hu says.
He and his colleagues are now conducting a study to see if calcium therapy will work against this harmful transfer. "Our suspicion is that it will be a pretty low-tech approach to this problem in clinical practice," he adds.
A report on the study appears in the July issue of Pediatrics.
Lead is a potent heavy metal that can damage brain cells, causing learning and behavior problems and, at extreme doses, seizures, coma and even death.
The Centers for Disease Control and Prevention (CDC) considers a blood lead level of 10 micrograms per deciliter to be the upper limit for children. That is usually applied to chronic exposure to the toxin, the kind that results from living amid lead paint dust.
The government estimates that 38 million houses and apartments have lead-based paint -- down from 64 million in 1990, but still posing a potential threat to millions of children. According to the CDC, nearly 900,000 children in this country between the ages of 1 and 5 have elevated blood lead levels.
David Jacobs, a lead hazard official at the U.S. Department of Housing and Urban Development, says children in low-income housing are more than twice as likely as those in middle- and upper middle-class homes to be exposed to excessive lead. "Low-income families tend to live in dilapidated housing" where lead paint and lead dust are rife, Jacobs says.
Jacobs says the latest study confirms that lead is a "long-term threat," and the "best treatment for lead poisoning is prevention of exposure" in the first place.
Hu's group compared the effects on early child development of elevated blood and bone lead levels in 197 Mexico City women and their children. People in Mexico have about double the lead exposure as those in the United States, he says.
Many factors influence infant growth and intelligence, from maternal and paternal educational attainment and IQ to the duration of breast-feeding and early childhood illness.
Even after considering these variables, higher lead levels in a woman's blood (taken from the umbilical cord) or in her bones (as measured by X-ray screening) was associated with worse scores on both physical and, to a greater degree, mental development tests.
Babies whose mothers were in the highest quarter of bone lead had mental development index (MDI) scores 6.5 points lower than those in the lowest 25 percent, Hu's group found. For every doubling in blood lead levels, a baby's mental index fell about three points -- consistent with earlier reports on the effect of the toxin.
"I think of this as coming to grips with the fact that many toxic exposures have long-term implications, even after we've addressed current exposures," Hu says.
Don Ryan, executive director of the Alliance to End Childhood Lead Poisoning, says the Boston study was yet another example of why taking lead out of the environment is so critical.
However, he adds, "if we're focusing on the pregnant mother here, we're missing the more important issue of preschool girls in the U.S. and elsewhere who are being exposed to lead today." Lead poisoning "is an environmental disease by origin and solution. The only real answer here is to aggressively control children's exposures to lead."
Jacobs adds that lead's effects aren't limited to females, and the poisonous metal can harm the reproductive organs of both boys and girls.
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