Even minute amounts of lead may take a toll on pregnant women, according to a study published by Lynn Goldman, M.D., M.S., M.P.H., Dean of George Washington University's School of Public Health and Health Services in D.C., and colleagues, in the journal Environmental Health Perspectives. Although the levels of lead in the women's blood remained far below thresholds set by the Centers for Disease Control and Prevention (CDC) and standards set by the Occupational Safety and Health Administration, women carrying more lead had significantly higher blood pressure.
"We didn't expect to see effects at such low levels of lead exposure," says Goldman, "but in fact we found a strong effect." If confirmed, this would indicate that pregnant women may be as sensitive to lead toxicity as young children.
Blood pressure is slightly higher during pregnancy, child labor, and delivery as the heart pumps harder. But prolonged high blood pressure during pregnancy (pregnancy-induced hypertension) can lead to complications called preeclampsia and then eclampsia. This potentially lethal condition also can predispose women to a heart attack in their future. While any increase in blood pressure during pregnancy is worrisome, the study did not find an association between lead and pregnancy-induced hypertension or preeclampsia.
The CDC advises to take action to reduce exposures when pregnant women or children have a blood lead level of 5 micrograms (ug) per deciliter (dL) or higher. However, very few studies have assessed the effect of lower levels of lead in pregnant women. Goldman feels that the recent study suggests that there are cardiovascular effects of lead in pregnant women at levels well below 5 ug/dL.
Of the 285 pregnant women monitored by the team at Johns Hopkins Hospital in Baltimore, Maryland, about 25% had a lead level higher than about 1 ug/dL of umbilical cord blood; it was these women who on average had a 6.9 mmHg increase in systolic pressure and a 4.4 mmHg increase in diastolic pressure. To arrive at these results, the team statistically controlled for other factors related to raised blood pressure, including ethnicity, obesity, anemia, household income and smoking.
"Hopefully our study will contribute to efforts to determine what a safe level of lead is for adults," said Ellen Wells, PhD, first author of the study and postdoctoral scholar at Case Western Reserve University School of Medicine in the Department of Environmental Health Sciences. The best way to reduce lead in women's blood is to prevent exposure, not only during but also prior to pregnancy. "Because lead is stored in bones for many years," Wells says, "even childhood exposure could impact lead levels in pregnancy."
Limiting levels of lead permitted in adults at the workplace might be a good place to start. "The occupational standard right now is a level of 40 um/dL," says Goldman, "and we see blood pressure changes at a level of 2."
Her words come at a pivotal time. On December 17, President Obama was asked to sign a bill into law that would reduce exposure to lead by tightening restrictions on lead in drinking water plumbing. The bill follows a series of investigations finding significant levels of lead in water in schools and in households in New York City and Washington, D.C. Although lead exposure has steadily declined in the U.S. since the nineties, primarily because of bans on lead in gasoline and drinking water regulations, this study suggests lead restrictions should remain a public health priority.
George Washington University Medical Center