Even Low Levels of Lead in Children’s Blood Negatively Affects Intelligence and Behavior
Heavy metals, such as lead are a part of our environment. Dishes with lead-based glazing, lead-crystal glasses, lead pipes, and lead-based paint are all common sources of lead exposure. Young children, because of their tendency to put things in their mouths, are at particular risk of ]]>lead exposure]]> .
As lead accumulates in the bodies of children, certain parts of their brains can become damaged leading to impairments of memory, learning, behavior, and coordination. Based on their interpretation of previous research, the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) determined that blood lead levels of 10 micrograms (µg) per deciliter or greater pose an unacceptably high risk of permanently harming children. Lower levels were considered safe.
However, a new study published in the April 17, 2003 issue of the New England Journal of Medicine concluded that even blood lead concentration levels below 10 µg per deciliter are associated with declines in children’s IQ scores, and social behavior skills, suggesting that more U.S. children may be adversely affected by environmental lead than previously thought.
About the study
The researchers measured blood lead concentration in 172 children between the ages of 6 months and five years and tested the IQs of these children between the ages of three and five years. (This study used the Stanford-Binet Intelligence test, in which a score of 100 is considered average intelligence and 70 is the cutoff number for mental retardation.) The relationship between IQ and blood lead concentration was determined and adjustments were made for the following variables: sex, birth weight, iron status, mother’s IQ, mother’s years of education, tobacco use during pregnancy, yearly household income, and the quality of the home environment.
The researchers found that blood lead concentrations were inversely and significantly associated with IQ. For every 10 µg per deciliter increase in average blood lead concentration, there was a corresponding 4.6 point decrease in IQ. In addition, the researchers found that among children whose maximum blood lead concentrations remained below 10 µg per deciliter, the change in IQ associated with a given change in lead concentration was even greater. The end result was an overall decline in IQ of 7.4 points as average blood lead concentrations increased from 1 to 10 µg per deciliter over a child’s lifetime.
How does this affect you?
The study’s findings suggest that considerably more U.S. children are adversely affected by environmental exposure to lead than previously estimated. It appears that the intellectual functioning of children between the ages of three and five is adversely affected even when their blood lead level is below the current level of concern according to CDC and the WHO standards. While the definition of an elevated blood lead level has been lowered over the past two decades, the results of this and other recent studies suggest that there is no safe blood lead level and that the adverse effects of an elevated blood lead level are both persistent and irreversible.
The observation that the effects of lead on IQ are proportionally greater at lower lead concentrations may seem counterintutive. The researchers suggest that because the presence of heavy metals in the blood triggers the body’s natural immune response, it is possible that higher blood lead levels trigger a stronger immune response than lower blood lead levels, resulting in less overall damage.
Because elevated blood lead concentrations pose a risk to the public health beyond their effects on intelligence and behavior in children—including cardiovascular disease, kidney disease and ]]>tooth decay]]> —the researchers suggest that instead of investigating how best to treat children with elevated blood lead concentrations, we focus on ways of preventing their exposure to lead in the first place.
The CDC recommends you take the following steps in order to limit you child’s risk of exposure to environmental lead:
- Make sure your child does not have access to peeling paint or chewable surfaces painted with lead-based paint.
- If your house was built before 1960, wet mop all hard surface floors at least once a week with a high (5% to 8%) phosphate solution. Other hard surfaces (such as window sills and baseboards) should also be wiped with a similar solution.
- Wash your child's hands and face before he or she eats.
- Wash toys and pacifiers frequently.
- If soil around the home is or is likely to be contaminated with lead, plant grass or other ground cover.
- In areas where the lead content of water exceeds the drinking water standard, use only fully flushed water from the cold-water tap for drinking, cooking, and making formula.
- Do not store food in open cans, particularly if the cans are imported.
- Do not use pottery or ceramic ware that was inadequately fired or is meant for decorative use for food storage or service.
- Make sure that your child is not being exposed to lead dust that you may be bringing into your home from your work or hobbies.
- Make sure your child eats regular meals, because more lead is absorbed on an empty stomach.Make sure your child's diet contains plenty of iron and calcium.
Centers for Disease Control and Prevention
World Health Organization
Canfield RL, Henderson CR, Cory-Slechta DA et al. Intellectual impairment in children with blood lead concentrations below 10 µg per deciliter. N Engl J Med. 2003;348(16):1517-1526.
Preventing lead poisoning in young children. U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control. Published: 10/01/1991.
Available at: http://wonder.cdc.gov/wonder/prevguid/p0000029/p0000029.asp
Last reviewed Apr 17, 2003 by ]]>Richard Glickman-Simon, MD]]>
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