posted 7 November 2006
Jouni J. K. Jaakkola, JJK, A Ieromnimon and MS Jaakkola. 2006. Interior Surface Materials and Asthma in Adults: A Population-based Incident Case-Control Study. American Journal of Epidemiology 164:742–749.
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This large study from Finland reports that adults working in rooms with plastic walling materials are more than twice as likely to develop asthma. Risk of asthma was also higher for people working in settings with wall-to-wall carpeting, especially in the presence of mold problems.
These results are consistent with prior studies showing increased asthma risk with exposure to the phthalate DEHP. Plastic walling and many carpets include polyvinyl chloride, which contains as much as 30-40% DEHP by weight DEHP, and where these materials are used, DEHP levels are elevated in dust.
Several studies have indicated DEHP can increase allergic reactions, including recent research with mice. The mouse research shows heightened allergic reactions at levels within the range of human exposure, with the strongest response at lower levels.
Context: Asthma rates have increased steadily and substantially in the developed world over the past 30 years, especially in children but also in adults. The total number in the US with asthma has doubled since 1980. This increase has taken place rapidly, at a time when there is no biological reason to think there has been a commensurate increase in allergens that would provoke an asthmaticresponse. Overall, air quality has improved substantially. This implies that something has increased baseline sensitivity to asthma-provoking agents. Phthalates have emerged as one candidate, because they resemble, at a molecular level, genetic signaling mechanisms used to adjust immune system sensitivity.
What did they do? Working in southern Finland, Jaakkola et al. identified all newly diagnosed asthma cases in the area from Sept 1997 to April 2000 (City of Tampere) and March 1998 to April 2000 (entire Pirkanmaa Hospital District) and solicited their involvement in the study. A total of 521 agreed to participate (86% response rate). They matched these cases with 932 controls, selected at random from the same population, excluding those with a history of asthma or those who did not meet age criteria.
Cases of asthma were confirmed by medical examination. The subjects were then interviewed about the use of plastic materials and carpets used in their homes and workplaces, as well as whether the homes had been renovated or painted. They were also asked about mold conditions and whether or not pets were present.
What did they find?
- Adults employed in a work environment within which at least half the walling is covered by plastic were more than twice as likely to be diagnosed with asthma (odds ratio 2.43, 95% confidence interval 1.03 to 5.75).
- People working in a setting with wall-to-wall carpeting without mold had an odds ratio of 1.43 (95% CI= 0.69 to 2.96)
- People working in a setting with mold but without wall-to-wall carpeting had an odds ratio of 1.39 (95% CI= 0.91 to 2.13)
- People working in a setting with both wall-to-wall carpeting and mold had an odds ratio of 4.64 (95% CI= 1.11 to 19.4 )
What does it mean? This study adds to a growing body of literature linking the phthalate DEHP to increases in asthma and allergic responses. It is the largest to date assessing determinants of adult-onset asthma. It demonstrates statistically significant associations between asthma risk and plastic wall covering and between asthma risk and wall-to-wall carpeting (in the presence of mold). Mold and carpeting independently showed a tendency toward increased risk which became statistically significant in combination.
Jaakkola et al. do not have direct measurements of phthalate exposures. The link to DEHP is indirect. It rests on the fact that plastic wall materials are made of PVC, that PVC contains up to 40% by weight DEHP, and that rooms with PVC walls have been shown to have DEHP-contaminated dust. Similarly, carpets usually have PVC backing that generates DEHP-contaminated dust (although some manufacturers have been to use replacements).
Jaakkola et al. comment "Our findings on the relations between plastic and textile surface materials and the risk of asthma are consistent with four recent epidemiologic studies in children conducted in Norway, Finland, Sweden, and Russi," each of which found links between PVC/DEHP and respiratory challenges.