Air pollution and hospitalization for headache


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Air pollution and hospitalization for headache

  1. 1. American Journal of Epidemiology Vol. 170, No. 8 ª The Author 2009. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. DOI: 10.1093/aje/kwp217 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (, which permits unrestricted non-commercial use, Advance Access publication: distribution, and reproduction in any medium, provided the original work is properly cited. September 9, 2009Original ContributionAir Pollution and Hospitalization for Headache in ChileRobert E. Dales, Sabit Cakmak, and Claudia Blanco VidalInitially submitted February 11, 2009; accepted for publication June 25, 2009. The authors performed a time-series analysis to test the association between air pollution and daily numbers of hospitalizations for headache in 7 Chilean urban centers during the period 2001–2005. Results were adjusted for day of the week and humidex. Three categories of headache—migraine, headache with cause specified, and headache not otherwise specified—were all associated with air pollution. Relative risks for migraine associated with interquartile-range increases in specific air pollutants were as follows: 1.11 (95% confidence interval (CI): 1.06, 1.17) for a 1.15-ppm increase in carbon monoxide; 1.11 (95% CI: 1.06, 1.17) for a 28.97-lg/m3 increase in nitrogen dioxide; 1.10 (95% CI: 1.04, 1.17) for a 6.20-ppb increase in sulfur dioxide; 1.17 (95% CI: 1.08, 1.26) for a 69.51- ppb increase in ozone; 1.11 (95% CI: 1.00, 1.19) for a 21.51-lg/m3 increase in particulate matter less than 2.5 lm in aerodynamic diameter (PM2.5); and 1.10 (95% CI: 1.04, 1.15) for a 37.79-lg/m3 increase in particulate matter less than 10 lm in aerodynamic diameter (PM10). There was no significant effect modification by age, sex, or season. The authors conclude that air pollution appears to increase the risk of headache in Santiago Province. If the relation is causal, the morbidity associated with headache should be considered when estimating the burden of illness and costs associated with poor air quality. air pollution; environment; headacheAbbreviations: ICD-10, International Classification of Diseases, Tenth Revision; PM2.5, particulate matter less than 2.5 lm inaerodynamic diameter; PM10, particulate matter less than 10 lm in aerodynamic diameter. Acute and chronic exposure to urban air pollution in tion were significantly worse (P < 0.05) when the womenNorth America and Europe has been associated with in- were exposed to ozone at 60–80 ppb as compared with <2creased respiratory symptoms, reduced lung function, and ppb (10). Between 1992 and 2000, the daily number ofhospitalization and death from cardiac and respiratory headache-related visits to an Ottawa, Canada, hospitaldiseases (1–5). emergency department increased by 4.9% (95% confidence Headache is an important cause of morbidity in modern interval: 1.2, 8.8) with each 3.9-ppb increase in sulfur di-society. There are many self-reported triggers for migraines, oxide level, lagged by 2 days (11). The same author alsoincluding weather, fatigue, stress, food, menstruation, and reported an increase in headache-related visits in Montreal,infections (6, 7). There have been few studies of the effect of Canada, associated with increases in nitrogen dioxide andair pollution on headache. A daily diary study of 32 head- carbon monoxide levels (12).ache sufferers in Turin, Italy, revealed that the severity and We studied the association between gaseous and particu-frequency of headache was related to numbers of days with late air pollution and hospitalization for headache in San-increased carbon monoxide and nitrogen dioxide levels (8). tiago Province, Chile. Santiago is densely populated and isReported headache was more common in a neighborhood situated in a valley surrounded by the Coastal and Andeswith a pulp mill than in one without one (9). Among 29 mountains (13–15). In 2001, Kavouras et al. (16) observedwomen aged 19–27 years who were studied in an environ- that concentrations of particulate matter less than 10 lm inmental chamber, headache, eye irritation, and nasal irrita- aerodynamic diameter (PM10) in several Chilean cities were Correspondence to Dr. Sabit Cakmak, Division of Statistics, Health Canada, 50 Columbine Driveway, Ottawa, Ontario, Canada K1A 0K9 (e-mail: 1057 Am J Epidemiol 2009;170:1057–1066
  2. 2. 1058 Dales et al.high by US and European standards, making it easier to each pollutant, using the optimal lags—those that maxi-detect adverse effects of air pollution. mized the observed effect size. The interquartile range, the middle 50% of the exposure data, provides a realistic es- timate of day-to-day changes. It is nonparametric, so it willMATERIALS AND METHODS not be influenced by skewed data. It excludes extremeAir pollution data values and outliers which are unstable and infrequently seen. Results from each region were pooled using a ran- Daily air pollution data from 2001–2005 for the urban dom-effects model.centers that make up Santiago Province were obtained from7 monitoring stations in 7 regions: Las Condes, Cerrillos, ElBosque, La Florida, Independencia, Santiago, and Pudahuel. RESULTSThe Las Condes, Santiago, and Pudahuel stations measuredthe pollutants ozone, nitrogen dioxide, sulfur dioxide, carbon Regional population sizes varied more than 3-fold, frommonoxide, PM10, and particulate matter less than 2.5 lm in 421,000 in Independencia to 1,335,000 in La Floridaaerodynamic diameter (PM2.5). Nitrogen dioxide was not (Table 1). The numbers of hospital admissions for headachemeasured in Independencia, La Florida, or El Bosque. varied 2- to 4-fold between Santiago and Independencia. InPM2.5 was not measured in Independencia. the total population of 5.37 million people, there was an average of 2.5 hospital admissions daily for headache, half of which had no specified cause and one-third of which wereHeadache hospitalization data for migraine. Twenty-four-hour mean concentrations of air Headache was coded using the International Classifica- pollutants varied by approximately 50%–100% between re-tion of Diseases, Tenth Revision (ICD-10). Daily numbers gions. El Bosque had the greatest concentrations of PM10of hospitalizations for migraine (ICD-10 code G43), other and sulfur dioxide and the second-greatest concentration ofspecified headache (tension, cluster, vascular, posttraumatic, sulfur dioxide. Las Condes had the greatest concentration ofdrug-related, or other specified cause; ICD-10 code G44), ozone.and headache not otherwise specified (ICD-10 code R51) The greatest and smallest regional pairwise correlationwere obtained from the Instituto Nacional de Estadisticas, coefficients for each 2-pollutant combination are presentedthe official source of statistical data in Chile from 2001 in Table 2. Those greater than or equal to 0.7 are identifiedthrough 2005. Atypical facial pain and trigeminal neuralgia with a footnote. The greatest positive correlations were be-were not included. tween carbon monoxide and nitrogen dioxide and PM2.5, which is consistent with a common source, mobile combus- tion. Sulfur had somewhat lower positive correlations withStatistical methods the other pollutants, whereas ozone tended to have small and We assumed a Poisson distribution and used time-series often negative correlations with other pollutants.analyses. A linear association between ambient air pollutionand headache on the logarithmic scale was assumed (17). Associations between headache and single pollutantsNatural splines were created with 1 knot for each of 15, 30,60, 90, 120, 180, and 365 days of observation. We selected The majority of relative risks for the relation between head-a model with the number of knots that minimized Akaike’s ache and air pollution were greater than 1 for each of the 7Information Criterion, a measure of model prediction. We areas and each of the 3 headache classifications (Table 3).then maximized the evidence that the model residuals did Of all of the relative risks calculated for each pollutantnot display any type of structure, including serial correlation by region and by headache type, ozone had greater relativeusing Bartlett’s test (18). We also plotted model residuals risks than the other pollutants for 14 of the 21 comparisons.against time, searching for visual signs of a pattern or cor- Of the 3 headache types, relative risks were greater forrelation. Having selected the optimal model for time, we migraine for approximately 50% of the comparisons. Theassessed the 24-hour mean values for temperature, humidity, 95% confidence interval excluded 1 for 15 of the 21 com-barometric pressure, and humidex (a measure of the com- parisons with ozone, 7 of the 12 comparisons with nitrogenbined effect of temperature and humidity; Environment dioxide, and 6 of the 12 comparisons with PM2.5. For otherCanada, unpublished data, 2002 ( pollutants, fewer than 50% of the comparisons were to determine the best icant. The number of times the 95% confidence intervalweather predictors of headache. We accounted for potential excluded 1 was 22 for migraine, 9 for nonspecified head-nonlinear associations with headache by using natural spline ache, and 7 for specified headache. Las Condes and Santiagofunctions with 4 knots. The model that minimized Akaike’s had the greatest numbers of significant relative risks. ThereInformation Criterion used humidex, both on the day of the were significant associations between migraine and ozone inhospital admission for headache and on the day prior. all regions. Lag times of 0–5 days were examined for the air pollut- When the regions were pooled, the relative risk estimatesants. We also used unconstrained distributed lags as de- were greater than 1 for all pollutant-headache type combi-scribed by Schwartz (19). nations. Using models with a single lag structure, the 95% In this paper, we present the increase in relative risk of confidence interval excluded 1, except for the associationsheadache for an interquartile-range increase in the level of between PM2.5 and migraine and headache of specified Am J Epidemiol 2009;170:1057–1066
  3. 3. Air Pollution and Hospitalization for Headache 1059 Table 2. Minimum and Maximum Pearson Pairwise Correlations Change 12.23 18.93 34.20 23.35 21.51 1-IQR Between Air Pollutants for 7 Urban Centers, Santiago Province, PM2.5, mg/m3 Table 1. Populations, Daily Numbers of Hospitalizations for Headache, and 24-Hour Ambient Air Pollution Concentrations in 7 Urban Centers, Santiago Province, Chile, 2001–2005 Chile, 2001–2005 Abbreviations: IQR, interquartile range; PM2.5, particulate matter less than 2.5 lm in aerodynamic diameter; PM10, particulate matter less than 10 lm in aerodynamic diameter. Carbon Sulfur Nitrogen b Mean Pollutant Ozone PM10 26.05 34.22 62.65 33.62 32.48 Monoxide Dioxide Dioxide Change Ozone 22.11 Minimum À0.514** 41.92 41.06 36.43 34.07 38.84 42.75 37.79 1-IQR PM10, mg/m3 Maximum À0.176 Sulfur dioxide b Mean 52.49 73.16 77.79 76.77 67.55 69.94 73.58 72.24 Minimum 0.418** À0.088* Maximum 0.821 0.129 Nitrogen dioxide Change 30.21 32.43 32.70 22.09 28.97 1-IQR 0.788a,** À0.339** 0.416** Dioxide, ppb Daily Air Pollution Concentration Minimum Nitrogen b Maximum 0.844a À0.085 0.797 PM10 Mean 52.77 44.43 44.72 40.13 44.74 Minimum 0.512** À0.003** 0.387** 0.614** Maximum 0.835 0.169 0.839 0.787 Change 1-IQR 3.74 8.62 7.25 5.47 6.33 6.27 4.91 6.20 PM2.5 Dioxide, ppb Minimum 0.729a,** À0.310** 0.390** 0.716a,** 0.712a,** Sulfur Maximum 0.915a À0.069 0.825 0.823a 0.917a b Mean 5.97 8.97 9.06 7.21 9.32 11.17 11.21 10.74 Abbreviations: PM2.5, particulate matter less than 2.5 lm in aerody- namic diameter; PM10, particulate matter less than 10 lm in aerodynamic Change diameter. 56.84 52.92 78.40 72.52 73.99 50.96 69.51 121.50 1-IQR * P < 0.05; **P < 0.005. a Ozone, Pearson pairwise correlation coefficient of 0.7 or greater. ppb b 88.52 81.28 83.52 96.20 82.73 93.26 124.10 101.41 Mean cause and the association between nitrogen dioxide and headache of specified cause (Table 4). The largest risk esti- Change Monoxide, ppm mate was 1.17 for the relation between ozone and migraine 1-IQR 0.57 1.13 1.22 1.28 1.27 1.40 1.04 1.15 headache, and the second-largest was 1.13 for the relation Carbon between nitrogen dioxide and headache of specified cause. Effect sizes seen with a distributed lag structure pointed in b Mean 0.81 0.94 1.24 1.27 1.06 1.21 1.09 1.11 the same direction but tended to be greater than with the single lag structure. With distributed lags, the only 95% Specified a confidence interval not excluding 1 was that for the associ- Cause 0.101 0.059 0.077 0.113 0.125 0.033 0.053 0.561 Daily No. of Hospitalizations, ation between migraine and PM2.5. There was no consistent by Headache Type effect modification of the headache-pollution associations by age, sex, or season (Table 5). Compared with younger Population weighted average pollutant concentration. Migraine a 0.127 0.095 0.095 0.138 0.150 0.053 0.086 0.744 persons, those over age 64 years had nonsignificantly larger Total number summed over all 7 urban centers. relative risks for headaches other than migraine. Otherwise Specified Associations for headache in 2-pollutant models a 0.114 0.057 0.104 0.102 0.135 0.046 0.061 1.168 Not For migraine, the relative risk point estimates for nitrogen dioxide remained stable and statistically significant after adjustment for each of the other pollutants (Figure 1). When Population a (3105) 5.01 8.92 9.15 4.21 4.98 8.08 13.35 53.70 other pollutants were adjusted for nitrogen dioxide, their point estimates decreased and statistical significance was lost. The point estimate for PM10 remained stable despite adjustment for pollutants other than nitrogen dioxide. Car- Combined results bon monoxide, sulfur dioxide, and ozone lost significance Independencia when adjusted for nitrogen dioxide or PM2.5. For both head- Center Urban Las Condes El Bosque La Florida Pudahuel ache–not otherwise specified and headache–specified cause, Santiago Cerrillos the results from 2-pollutant models were similar. The rela- tive risk point estimate for carbon monoxide remained sig- a b nificant when adjusted for other gases but lost significanceAm J Epidemiol 2009;170:1057–1066