Bornehag, CG, J Sundrell, CJ Weschler, T Sigsgaard, Björn Lundgren, Mikael Hasselgren, Linda Hägerhed-Engman. 2004. The Association between Asthma and Allergic Symptoms in Children and Phthalates in House Dust: A Nested Case-Control Study, Environmental Health Perspectives
Background on phthalates
Background on asthma
This study links exposure to phthalates found in household dust to rhinitis, eczema, and asthma in children.
Both asthma and allergies are serious childhood diseases that are increasing at alarming rates. Asthma is the most common chronic disease in US children, with rates more than doubling since 1980. Many factors are known to trigger asthma attacks, but the causes for the overall increase in asthma rates is unknown [more...]. Eczema is one of the most common skin diseases in infants and children, and has increased at least 30% since 1970, according to the American Academy of Dermatology.
Phthalates are industrial chemicals used widely in modern commerce. Over the last several decades, exposure to phthalates has become ubiquitous and virtually unavoidable. There are many types of phthalates, each with its own chemical and physical properties and toxicological characteristics.
What did they do?
Bornehag et al. conducted a nested case-control study of children ages 3-8 in Sweden. The researchers identified 198 cases and 202 controls using an initial and a follow-up questionnaire. The children were examined later by a physician who confirmed the diagnoses. To be classified as a case, participants had to have experienced at least two of the following symptoms in the year prior: wheezing without a cold, rhinitis or eczema. ‘Controls’ reported no allergic symptoms on either questionnaire. The questionnaire results mostly agreed with the physicians’ diagnoses.
During the same two-week period in which doctors examined all of the children, researchers collected dust samples, performed visual inspections, and conducted indoor air quality assessments in the children’s homes. Children were excluded from the study if their homes had been rebuilt because of moisture problems, or if they had moved since the first questionnaire. In laboratory testing, different types of phthalates found in the dust samples collected from the children’s bedrooms were identified and quantified.
The researchers also recorded the presence of PVC flooring in homes (phthalates are added to PVC to alter its physical characteristics).
Bornehag et al. used several statistical analyses to examine links between each of the three physician-diagnosed health conditions (asthma, eczema, or rhinitis) and phthalate concentrations in bedroom dust. Exposure to environmental tobacco smoke and other factors that could influence the results of the study were taken into account.
What did they find?
Children diagnosed with asthma or allergies had significantly higher levels of phthalate in dust collected from their bedrooms than did healthy children. They were also more likely to live in homes with PVC flooring. Dust from bedrooms with PVC flooring were more likely to have higher concentrations of BBzP and DEHP compared to other bedrooms.
The associations were different for different types of phthalates. Children diagnosed with either rhinitis or eczema had significantly more BBzP in bedroom dust than did controls.
Children diagnosed with asthma had significantly more DEHP in the dust collected from their bedrooms than did controls.
The researchers found a dose-response relationship between the concentrations of phthalates in the dust and the likelihood of being diagnosed with asthma, rhinitis, or eczema. The higher the concentration, the more likely a child was to be diagnosed with one of the 3 diseases.
Children with the highest levels of phthalates in their bedroom dust were between 2 and 3 times more likely to be diagnosed with asthma, rhinitis, or eczema compared with children with the lowest levels of phthalates in their bedroom dust.
The graph to the left shows two dose-response relationships observed by Bornehag et al. Asthma risk was higher where DEPH levels were higher, and rhinitis risk was higher with higher BBzP levels.
Their analyses took into account a series of variables that might confound the results, including sex, age, smoking at home, and type of building.
Children diagnosed with one of the conditions were also more likely to have PVC flooring in their bedroom. As the researchers point out, however, the link between BBzP/DEHP and health effects is not due simply to these chemicals association with PVC.
Bornehag et al. suggest that the different health patterns seen between DEHP vs BBzP and these health conditions result from differences in their toxicological and physicochemical properties. Not only does each phthalate have different metabolic pathways in humans and laboratory animals, and also different toxicological profiles, exposure pathways differ also. More than 85% of airborne DEHP is associated with airborne particles, whereas BBzP tends to be present as a gas. Substances in a gas phase deposit in the lungs differently than those attached to particles.
What does it mean?
This is the first epidemiological study to link phthalates strongly with asthma and allergies.
The authors note that previous studies suggest that some phthalates act as adjuvants. Such findings add biological plausibility to the link that Bornehag et al. report in this paper because they suggest mechanisms by which phthalates could be having effects.
Their results are consistent with a model proposed in 1997 for the possible role of phthalates in causing asthma. This model was based upon observations that the primary metabolite of DEHP, called MEHP, structurally resembles key natural molecules used by the immune system to heighten sensitivity. In the model, MEHP causes asthma by mimicking these molecules, called prostaglandins and thromboxanes, binding with the natural receptors for these molecules, and then turning on genes that lead to hypersensitivity of respiratory tissues. This increases the risk of inflammation in the airways.
Considering the recent dramatic increases in both asthma and allergies and the ubiquity of phthalates in the environment, these results have global implications for public health. Roughly 3.5 million metric tons of phthalates are produced each year worldwide for use in plastics, cosmetics, adhesives, dyes and building materials like PVC flooring. Studies in Germany, the US and Italy have found surprisingly high levels of phthalates in people.
Because of the rapid pace at which asthma has increased, environmental causes must be involved; the change has taken place too rapidly to be explained by inherited factors [more...].
According to the research team, “while there are likely multiple factors responsible for the increases in allergies and asthma that have been documented in developed countries over the past 30 years, it is striking that these increases have occurred during a period when plasticized products have become ubiquitous in the homes, schools and workplaces of the developed world.”
Some of the phthalates mentioned in this study (information from this study and its sources):
- DEHP: di(2-ethylhexyl) phthalate. Used mostly in PVC plastics, which typically can contain 30% DEHP by weight.
- DnBP: di-n-butyl phthalate. Used in latex adhesives, nail polish and other cosmetic products, as a plasticizer in cellulose plastics, as a solvent in some dyes, and as a plasticizer in PVC.
- BBzP: n-butyl benzyl phthalate. Used as a plasticizer for vinyl tile, carpet tile and artificial leather, and also in some adhesives.
For more background on phthalates