The danger of lead poisoning is well known, but how best to protect infants from its effects hasn’t been established. Scientists have now shown that by taking calcium supplements during pregnancy, a mother can significantly reduce the lead exposure of her fetus. Unfortunately, the protection isn’t complete.
Lead is chemically similar to calcium, so some adults carry lead in their skeletons. During the late stages of pregnancy, a mother’s bones sometimes dissolve slightly to provide her baby with calcium for its skeleton. Scientists thought that providing plenty of calcium to a pregnant woman would prevent her bones from dissolving and thus keep locked in her skeleton whatever lead had accumulated there during her life.
Brian L. Gulson, a geochemist at Macquarie University in Sydney, Australia, and his team studied 10 pregnant women who had immigrated recently from Central and Eastern Europe to Australia. The researchers gave the women daily calcium supplements starting early in their pregnancies. Moreover, the women ate a regimented diet with known amounts of calcium.
The researchers also measured environmental lead to which the prospective mothers were exposed, such as in household dust and drinking water.
Once a month during the pregnancies and for 6 months after the women gave birth, the researchers took blood samples from the mothers, eight of whom completed the study. All the women’s blood-lead concentrations began increasing when they were 6 to 8 months into their pregnancies, the researchers report in an upcoming Environmental Health Perspectives.
In an earlier study, Gulson had found that pregnant women who didn’t take calcium supplements and got much less than the recommended daily amount of calcium showed this “lead mobilization” much earlier, beginning 3 to 6 months into pregnancy.
“The most encouraging thing is that lead mobilization was delayed,” says Gulson, “but it’s disappointing that it happened at all.”
The researchers used a sensitive chemical test in examining the women’s blood to differentiate between lead from the bones and lead from the diet or environment. The lead the women accumulated before immigrating was slightly different from the lead they were exposed to in Australia.
Compared with the women in the earlier study who didn’t get enough calcium, women taking calcium supplements had only half as much lead seep out of their skeletons. The fetuses probably used some of the calcium from the supplements in their bone development, causing their mothers’ bones to release less calcium and lead, says Gulson.
After the eight women gave birth, their blood-lead concentrations increased even further as their bones continued dissolving to provide calcium for breast milk, says Gulson. “Unfortunately, the calcium supplement doesn’t seem to have any effect on blood-lead levels while [women are] lactating,” he says.
“This is a very important study which apparently shows some positive effects of calcium supplementation,” says Howard Hu of the Harvard School for Public Health. However, Hu says he would have liked to have seen a larger sample size or a control group in the study.
Gulson says that the expense of the highly sensitive lead tests kept the current study small.
Obstetricians already recommend calcium for protecting mothers’ bones, and Hu notes that supplements also cut lead exposure of fetuses. “There’s almost no downside,” he says.
Gulson points out that no one has established the relationship between lead in the blood and in breast milk. However, the benefits of breast-feeding more than offset any risk of transmitting lead to an infant, he says.