13 Jun 1996: NIH-Supported Studies Show Potential Danger to Fetus from Expectant Mothers' Own Early Exposure to Lead
Preliminary results from two studies funded by the National Institute of Environmental Health Sciences, one of the National Institutes of Health, suggest that lead accumulated in a pregnant woman's bones over her lifetime can leach out during pregnancy, exposing the developing fetus.
The early results were discussed during a funding review at the institute. Because of the importance of lead exposure in minority neighborhoods, the studies are also being funded in part by the NIH Office of Minority Health Research.
The early data from one of the studies suggests that 40 to 60 percent of the lead in pregnant women's blood comes from lead accumulated in the bones from exposures from years past and leached out, much later, during pregnancy. This study is being carried out by Brian Gulson, Ph.D., and other researchers at Macquarie University and the Commonwealth Scientific Industrial Research Organization, both in Sydney, Australia.
The other NIEHS-supported study suggests that much of the lead is released during the second and third trimester, when the fetus is drawing on its mother's calcium for its own bone development. This work was conducted by Health and Welfare Canada researchers led by Claire Franklin, Ph.D., who observed and tested pregnant monkeys.
Previous studies indicate that lead in the mother's blood crosses the placenta and enters the unborn child's bloodstream but NIEHS scientists said further study will be needed to show that the pass-through is enough to affect the fetus' development.
Lead is known to cause developmental delays in children even at moderate levels in the blood, and retardation at higher levels. "We have known that lead accumulates in bone, but until now we didn't know if the stored lead of a mother-to-be re-entered the blood during pregnancy," William Jameson, Ph.D., the NIEHS project director on both studies, said. "Now we know it does-and that a girl growing up in a lead-polluted environment might, years later, pass on that lead to her offspring."
Dr. Jameson said the human study is especially ingenious in design:In order to determine whether lead came from earlier accumulationsin the mothers' bones, the researchers in Australia are lookingat young women who have come to Australia from Eastern Europe,where the lead has a different molecular weight.
By determining lead is in the bloodstream, the researchers can thus show how much is from old lead exposures accumulated in the bone and how much from newer exposures. The study, to involve as many as 100women, is expected to continue for another three years.
Both the animal and human studies monitor blood lead levels before,during and after pregnancy as well as lead levels in breast milk,food and the living environment.
The Canadian animal study shows that substantial lead is released from mothers' bones in the second and third trimester. The fetus' demand for calcium for bone formation at this time may draw on the mothers' bones, bringing the stored lead with the calcium.
Dr. Jameson said that the more that is known about lead's storage and movement in the body, the better its effects can be counteracted. For example, he said, calcium supplements possibly could be used to place calcium in the bloodstream for the fetus to draw on. This might reduce the amount of calcium-and lead-the child draws from the mother's bone.
NIEHS Director Kenneth Olden, Ph.D., said, "The best countermeasure remains preventing exposure to lead altogether through clean-up and replacement of older housing with leaded paint in both lower socioeconomic neighborhoods and newly stylish 'gentrified' areas. This may take years, so any other, quicker ways to reduce exposure that may come out of this research would be a welcome way to help children reach more of their potential."
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