In the study to be published Oct. 3 in Environmental Health Perspectives, the journal of the National Institute of Environmental Health Sciences (NIEHS), researchers found significantly higher blood lead levels in children who were iron-deficient than in children with normal blood iron levels.
While other studies have been done on blood lead and iron levels in children, this is the first study to take into account environmental lead contamination, said Asa Bradman, Ph.D., associate director of the Center for Children’s Environmental Health Research at UC Berkeley’s School of Public Health and lead author of the report. Bradman conducted the study while he was a public health doctoral student at UC Berkeley and an environmental health scientist at the Childhood Lead Poisoning Prevention Branch of the California Department of Health Services, which supported the study.
Paint, dust and soil samples were taken from the homes of 319 Sacramento-area children from ages 1 to 5 who were participating in a lead exposure survey by the state health department. Researchers tested blood samples taken from the veins of the children for lead and ferritin, an iron-storage protein considered an early marker of iron-deficiency. Ferritin levels greater than 12 micrograms per liter were considered normal.
"In almost all situations where the ferritin is low, the blood lead level is significantly higher," said Bradman. "The difference becomes even more significant in more (lead) contaminated environments."
Overall, the authors found that iron-deficient children had an average blood lead level of 5.6 micrograms per deciliter, or 1 microgram per deciliter higher than children with normal blood levels of iron. But in highly contaminated environments, iron-deficient children had average blood lead levels that were 2.8 micrograms per deciliter higher than children with sufficient iron in their blood. Lead is considered toxic at blood levels above 10 micrograms per deciliter.
Iron is a component of hemoglobin, a protein that helps the red blood cells carry oxygen throughout the body. Iron levels that drop low enough can lead to anemia, a condition where not enough red blood cells are produced. Symptoms of iron deficiency include decreased physical activity, inattentiveness, and delays in cognitive development.
One theory for the association between iron and lead levels in the blood comes from the fact that the two are biochemically similar. Many symptoms of severe iron deficiency even mimic those of lead poisoning. The absence of iron creates a nutrient deficit in the body, which responds by grabbing more of the lead that is ingested by the child, or hanging onto the lead more strongly once it is in the body, explained Bradman.
The association between iron-deficiency and higher blood lead levels held across all ethnic groups in the study with the major exception of Asian children. In that group, children with normal blood iron status had higher blood levels of lead than iron-deficient children.
"We spoke with people in Asian health centers and Asian health clinics, but we couldn’t come up with an explanation that was meaningful or plausible," said Bradman. "It could be chance alone, or something more meaningful that other investigators should look into."
The anomaly of the Asian children's results did not alter the overall significance of the data, Bradman noted. "It does prove that it is important to try to understand the intra- and inter-ethnic differences in environmental lead exposures," he said.
Iron deficiency and nutritional deficits disproportionately affect low-income families and minorities, the same groups who are more likely to be living in environments contaminated with lead. People living in homes built before 1955, when paint companies reduced the high levels of lead in house paint, are at greater risk for exposure, particularly if the home is in disrepair. Lead in house paint was completely banned in 1978 by the Consumer Products Safety Commission.
According to the federal Centers for Disease Control and Prevention (CDC), iron deficiency is the most common nutritional deficiency worldwide. Infants younger than 2 years old are particularly susceptible to iron deficiency because of their rapid rate of growth. The U.S. Recommended Dietary Allowance (RDA) for iron is 10 milligrams per day for children from age 6 months to 10 years. Good dietary sources of iron include lean meat, dark green leafy vegetables, legumes, and iron-fortified cereals.
"We need a better understanding of the nutritional factors in preventing lead exposure," said Bradman. "Iron is an important factor in preventing lead exposure and lead intoxication. The argument here is that health care providers should be careful to pay attention to the nutritional status of children."
But while a healthy diet is important, Bradman emphasized that nutritional factors are secondary to controlling the lead exposure from the environment. "You can have lots of iron, but if you're in a house with lots of lead, you're not going to get proper protection (from your diet alone)," he said. "We should be improving the whole environment of the child by improving both nutritional factors and reducing lead in children’s environments."
Co-authors of the study are Brenda Eskenazi, Ph.D., director of the Center for Children's Environmental Health Research at UC Berkeley's School of Public Health; Patrice Sutton and Marcos Athanasoulis, both of the California Department of Health Services; and Lynn Goldman, M.D., professor of Environmental Health Sciences at The Johns Hopkins University.
Note: The study can be viewed online at http://ehpnet1.niehs.nih.gov/docs/2001/109p1079-1084bradman/abstract.html. For more information about preventing lead exposure in children, call the Childhood Lead Poisoning Prevention Branch of the California Department of Health Services at 510-622-5000.
Journal
Environmental Health Perspectives