Prenatal lead exposure heightens childhood allergies.
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Jedrychowski, W, F Perera, U Maugeri, RL Miller, M Rembiasz, E Flak, E Mroz, R Majewska and M Zembala. Intrauterine exposure to lead may enhance sensitization to common inhalant allergens in early childhood. A prospective prebirth cohort study. Environmental Research http://dx.doi.org/10.1016/j.envres.2010.11.002. |
Context
Allergies are a body’s overreaction to a foreign substance – an allergen. These allergens can be eaten, inhaled, or touched. Often, the overreaction results in coughing, sneezing or a runny nose. Sometimes, an even stronger reaction can result in hives, difficulty breathing and even death.
Allergies are very common in the United States. About 50 million people have some type of allergy, and more than half of children in the United States are allergic to something in the air or food.
All the causes of allergies are not known. Exposure – or lack of exposure – to certain allergens before birth or early in life, coupled with genetics, probably explain some causes of allergies. Allergies are more common in cities and industrialized counties, leading many to believe that something about the urban environment – air pollution, bacteria or social factors – may also be partially responsible.
The metal lead is a common environmental pollutant in inner cities and in older houses. It can be released from factories and during mining operations. Lead is also found in consumer products, such as electronics and jewelry.
People are exposed to lead through eating, drinking, breathing or touching. Old paint in buildings and contaminated soil and dust pose the biggest sources for children.
Lead exposure has been linked to numerous health effects, including permanent changes to the nervous and reproductive systems. Lead is widely known as a neurotoxin, and as such, can impair brain development and lead to problems with behavior, cognition and motor skills.
Even small amounts of lead can affect the brain, therefore, the Centers for Disease Control considers there is no safe level of lead exposure for children.
Animal and laboratory research studies suggest that lead may also disrupt normal immune system development, which could lead to allergies and asthma. One study found that children living in areas polluted with metal-laden dust had more lifetime allergy problems than children from another, cleaner region.
What did they do?
The researchers examined children born to women in Krakow, Poland. The mothers were enrolled in the study while they were pregnant.
The researchers measured the amount of lead, mercury and markers for polycyclic aromatic hydrocarbons in the children's cord blood at birth to determine their prenatal exposure to these contaminants. They also measured cotinine in the cord blood to determine the children’s exposure to environmental tobacco smoke while in the womb.
When the children were three years old, researchers measured concentrations of certain allergens in the house dust. When they were five years old, researchers repeated the blood analyses from the contaminants, and the children were evaluated for allergies using a skin prick test.
What did they find?
Prenatal exposure to lead was significantly associated with having allergies at age five. Children who had the highest levels of lead in their cord blood were twice as likely to have allergies than children with lower levels. This link remained after other variables were taken into account, including gender, maternal age and education, and tobacco smoke exposure.
Overall, the geometric mean of blood lead levels in the cord blood was 1.16 micrograms per deciliter of blood (ug/dL). Blood lead levels were significantly higher (1.34 ug/dL) in cord blood of children who later developed allergies than in the cord blood of children without allergies (1.14 ug/dL).
Lead levels in the mothers' blood had the same pattern. Blood lead levels were significantly higher in the women whose children had higher lead levels in their cord blood than the mothers whose children had lower levels of lead in their cord blood.
Other prenatal exposures, including mercury and tobacco smoke, were not linked to allergies during childhood.
Of the 224 children who underwent allergy testing at age five, 17 percent were allergic to at least one allergen. The most common allergy was to dust mites (13 percent).
Mean blood lead levels in the 5-year-old children were about two times higher than that found in the cord blood at birth. Interestingly, levels of lead in the children’s blood at age five were not associated with having allergies.
What does it mean?
Exposure before birth to even very low levels of the metal lead can enhance sensitvitiy to allergens and increase the liklihood of allergies during childhood.
Importantly, lead's broad health effects may reach out into the immune system. The results suggest lead exposure during critical, prenatal periods of development can impact immune system function well after birth. In this case, the immune system is changed so it overreacts to common particles in the environment.
The results are consistent with prior studies and add more data to the growing story of how metals may trigger allergies. Prior animal studies show that mice exposed to metals produce more IgE – a key mediator of allergies. Other published human studies also find that metals are linked to increased allergic reactions and responses (Lutz et al. 1999).
The results also narrow the search for what metals may be responsible. While lead was linked with increased allergies in the children, mercury and the other chemicals measured in the study were not. Exposure after birth was also not linked to the increased allergic responses.
A limitation of this study is the potential role of other factors that are commonly found in conjunction with lead exposure. For example, in the United States, exposure to lead through substandard housing is frequently associated with lower socioeconomic status. Other enironmental factors may also play a role. Air pollution, for instance, can be a common exposure to both pregnant women whose children had/have higher exposure to lead and the children themselves.
Given the growing burden of allergies, asthma and other respiratory diseases in children – especially those in the more polluted inner-city areas – further research is needed to better understand environmental exposures to metals and their role in the development of childhood allergies.
ResourcesAmerican Academy of Allergy, Asthma and Immunology Asthma and Allergy Foundation of America Gao, D, TK Modal and DA Lawrence. 2007. Lead effects on development and function of bone marrow-derived dendritic cells promotes Th2 immune responses. Toxicology and Applied Pharmacology 222:69-79. Lead. Centers for Disease Control and Prevention. Lutz, PM, TJ Wilson, J Ireland, AL Jones, JS Gorman, NL Gale, JC Johnson and JE Rabinowitz, MB, EN Allred, DC Bellinger, A Levitan and HL Needleman. 1990. Lead ToxFAQs for Lead. Agency for Toxic Substances and Disease Registry.
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Lead and children
