Biomedical subjects

D Dockery

Publications and source records attributed to D Dockery.

13 recordsLinked to original sources

PubMed2001

Relation of body mass index to asthma and atopy in children: the National Health and Nutrition Examination Study III.

BACKGROUND: An increase in the prevalence of obesity and asthma over recent decades has been reported in affluent societies. Both overweight and obesity have been shown to be inversely related to having been breastfed, which is also a potential protective factor against childhood atopic diseases. The aim of this analysis was to explore the relation of body mass index (BMI) to asthma and atopy in a large representative sample of the United States population. METHODS: Children aged 4-17 years were included in the NHANES III survey. Prevalences of atopic diseases and potential confounding factors such as exposure to environmental tobacco smoke, birth weight, breast feeding, and household size were assessed using structured interviews with parents. Height and weight were measured, and BMI was calculated as kg/m(2) and transformed into Z scores. Children underwent skin prick tests for atopy to a battery of food and inhalant allergens. RESULTS: The prevalence of asthma (8.7% v 9.3% v 10.3% v 14.9%, p=0.0001) and atopy (48.6% v 50.5% v 53.0% v 53.2%, p=0.05) rose significantly with increasing quartiles of BMI. After adjustment for confounders, a significant positive association between BMI and asthma remained (adjusted OR 1.77, 95% confidence interval 1.44 to 2.19 between the highest and lowest quartiles of BMI), whereas no independent relation between BMI and atopy was evident. No effect modification by sex or ethnic group was seen. CONCLUSIONS: The effects of increased BMI on asthma may be mediated by mechanical properties of the respiratory system associated with obesity or by upregulation of inflammatory mechanisms rather than by allergic eosinophilic inflammation of the airway epithelium.

Adolescent↗

PubMed2000

Maximal and partial expiratory flow rates in a population sample of 10- to 11-yr-old schoolchildren. Effect of volume history and relation to asthma and maternal smoking.

The effect of volume history on forced expiratory flow rates has been reported to differ between patients with asthma and healthy persons, and it has been hypothesized that the peripheral airway inflammation of patients with asthma may underlie this difference. There are no published data, however, on the distribution of such volume history effects or the relation of these effects to airways disease in children. We obtained combined partial and maximal forced expiratory flow-volume curves on 1,834 children, age 10-11 yr, in eight communities in the United States and Canada. The effect of a deep inhalation on forced expiratory flow rates at low lung volumes was quantitated by the ratio of V (30) during a maximal expiratory maneuver (V (30M)) to V (30) during a partial expiratory maneuver (V (30P)). The V (30M)/V (30P) ratio was slightly higher among girls than boys (1.26 versus 1.18, p = 0.0001) indicating that a deep inhalation increased V (30) slightly more among girls than among boys. The V (30M)/V (30P) ratio was related to neither history of asthma nor to maternal smoking. In contrast, most spirometric indices from either the maximal or the partial expiratory flow-volume curve were lower in association with a history of asthma or a report of maternal smoking. The ratio of FEF(25-75)/FVC was particularly consistent as a measurement that discriminated both of these effects in boys and girls. These results suggest that the measurement of volume history effects offers no benefits for epidemiological studies of childhood respiratory disease whereas spirometric indices such as the FEF(25-75)/FVC ratio are quite sensitive to the effects of asthma and environmental tobacco smoke exposure on the airways.

Asthma↗

PubMed2000

Exposure measurement error in time-series studies of air pollution: concepts and consequences.

Misclassification of exposure is a well-recognized inherent limitation of epidemiologic studies of disease and the environment. For many agents of interest, exposures take place over time and in multiple locations; accurately estimating the relevant exposures for an individual participant in epidemiologic studies is often daunting, particularly within the limits set by feasibility, participant burden, and cost. Researchers have taken steps to deal with the consequences of measurement error by limiting the degree of error through a study's design, estimating the degree of error using a nested validation study, and by adjusting for measurement error in statistical analyses. In this paper, we address measurement error in observational studies of air pollution and health. Because measurement error may have substantial implications for interpreting epidemiologic studies on air pollution, particularly the time-series analyses, we developed a systematic conceptual formulation of the problem of measurement error in epidemiologic studies of air pollution and then considered the consequences within this formulation. When possible, we used available relevant data to make simple estimates of measurement error effects. This paper provides an overview of measurement errors in linear regression, distinguishing two extremes of a continuum-Berkson from classical type errors, and the univariate from the multivariate predictor case. We then propose one conceptual framework for the evaluation of measurement errors in the log-linear regression used for time-series studies of particulate air pollution and mortality and identify three main components of error. We present new simple analyses of data on exposures of particulate matter < 10 microm in aerodynamic diameter from the Particle Total Exposure Assessment Methodology Study. Finally, we summarize open questions regarding measurement error and suggest the kind of additional data necessary to address them.

Air Pollution↗

PubMed1999

A case-crossover analysis of air pollution and mortality in Philadelphia.

This study reassessed Schwartz and Dockery's analysis of daily mortality from nonexternal causes among residents of Philadelphia, Pennsylvania, over 8 years, from 1973 to 1980 [American Review of Respiratory Disease 145:600-604 (1992)]. A Poisson regression analysis using the same model found that a 100-microg/m(3) increment in the 48-hr mean concentration of total suspended particulates (TSP) was associated with increased all-cause mortality [rate ratio = 1.069; 95% confidence interval (CI), 1.043-1.096) after adjustment for quadratic trend, season, year, previous day's mean temperature, dew point, winter temperature, and indicators of hot (temperature > 80 degrees F) and humid days (dew point > 66 degrees F). Critics suggested that time-varying factors such as season and day of week were not sufficiently controlled in this analysis and subsequent studies in other locations. We used a conditional logistic regression analysis with a case-crossover design to reanalyze the data, with air pollution in the prior and subsequent weeks to the day of death serving as referent periods. The case-crossover approach controls for season and day of week by design rather than modeling. We found that a 100-microg/m(3) increment in the 48-hr mean level of TSP was associated with increased all-cause mortality [odds ratio (OR) = 1.056; CI, 1.027-1.086) after adjustment for the same weather variables as above. Similar associations were observed for deaths in individuals over 65 years of age (OR = 1.074; CI, 1. 037-1.111) and for deaths due to cardiovascular disease (OR = 1.063; CI, 1.021-1.107). The current case-crossover analysis confirms the general conclusion of the previous Poisson regression analysis of an association of TSP with daily mortality in Philadelphia, Pennsylvania.

Adolescent↗

PubMed1997

Experiences with the severity scoring of atopic dermatitis in a population of German pre-school children.

Severity scoring of atopic dermatitis (SCORAD) was introduced as a standard tool but has not been used in a population-based epidemiological study; the objective of the present study was to determine the practicability of this instrument in this setting. We assessed the distribution of the severity of atopic eczema in the community and investigated differences between east and west Germany. A factor analysis was then carried out to characterize the variables of this scoring system and to analyse possible relationships within them. A multicentre cross-sectional study was carried out in five east German and two west German locations in 1994; pre-school children (5-6 years old) were investigated and cases of atopic eczema identified by a dermatological examination. The SCORAD was used to determine the severity of atopic eczema and the results assessed using analysis of variance and principal component analysis (varimax rotation). In all, 1511 (76.2%) of the children originally contacted participated and 11.3% were diagnosed with atopic eczema at the time of examination. The median severity scores was 21.4 (interquartile range 13.5) and there was a tendency to higher scores in west Germany for the mean overall score, the intensity score and the extent. 'Erythema' (1.30 vs. 1.06; P = 0.006) and 'excoriation' (0.77 vs. 0.36; P = 0.002) were significantly more prominent in children with eczema from west Germany (adjusted for observer). Interobserver variabilities of the SCORAD parameters were calculated, adjusted for location and were in accordance with earlier findings. Principal component analysis identified three independent factors accounting for 54.1% of the total variance. A severity factor, characterized by 'extent', 'lichenification', 'excoriation' and 'pruritus', was separated from a factor with an acute eczema-type profile ('erythema', 'oedema', 'oozing') and a factor whose major characteristics were 'extent', 'dryness', and 'sleep loss'. We conclude that atopic eczema is frequent in pre-school children. The SCORAD proved to be readily applicable and useful in epidemiological studies, but further validation is needed.

Analysis of Variance↗

PubMed1995

Acute effects of ozone on the pulmonary function of exercising schoolchildren from Mexico City.

The acute effects of ozone (O3) on the change in lung function before and after exercise was assessed in 22 boys and 18 girls from 7 1/2 to 11 yr of age tested up to eight times over a 1 1/2-yr period outdoors (under a tarpaulin) at a school in Mexico City. Ozone and particulates were monitored at an adjacent government station, in the school yard, and under the tarp. Subjects were selected to oversample children with chronic respiratory symptoms, although children with active asthma under regular medication or FEV1 < 80% predicted were excluded. Of the participants, 21 had chronic cough, chronic phlegm, or ever wheeze with colds or apart from colds. Children performed two cycles of treadmill exercise (15 min) and rest (15 min) for a total of 1 h of intermittent exercise. Most subjects attained the target minute ventilation of 35 L/min/m2. Subjects exercised alternately during low ozone hours (8:00-10:00 A.M.) and during peak O3 hours (12:00-2:00 P.M.), to assure a range of exposures. On 85% of exercise days, the maximum daily 1-h average for ambient O3 exceeded the Mexican guideline of 110 parts per billion (ppb). O3 exposure during the hour of exercise was divided into quintiles, and the response was adjusted for repeated measures, subject having a cold, and prior outdoor exercise. Ambient O3 in the fifth quintile (mean = 229 ppb) was associated with a percentage change in FVC (-1.43% +/- 0.70), FEV1 (-2.85% +/- 0.79), FEF25-75% (-6.32 +/- 1.87) and FEV1 (-1.41% +/- 0.46).(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗

PubMed1993

Air pollution and daily mortality in Erfurt, east Germany, 1980-1989.

In Erfurt, Germany, unfavorable geography and emissions from coal burning lead to very high ambient pollution (up to about 4000 micrograms/m3 SO2 in 1980-89). To assess possible health effects of these exposures, total daily mortality was obtained for this same period. A multivariate model was fitted, including corrections for long-term fluctuations, influenza epidemics, and meterology, before analyzing the effect of pollution. The best fit for pollution was obtained for log (SO2 daily mean) with a lag of 2 days. Daily mortality increased by 10% for an increase in SO2 from 23 to 929 micrograms/m3 (5% quantile to 95% quantile). A harvesting effect (fewer people die on a given day if more deaths occurred in the last 15 days) may modify this by +/- 2%. The effect for particulates (SP, 1988-89 only) was stronger than the effect of SO2. Log SP (daily mean) increasing from 15 micrograms/m3 to 331 micrograms/m3 (5% quantile to 95% quantile) was associated with a 22% increase in mortality. Depending on harvesting, the observable effect may lie between 14% and 27%. There is no indication of a threshold or synergism. The effects of air pollution are smaller than the effects of influenza epidemics and are of the same size as meterologic effects. The results for the lower end of the dose range are in agreement with linear models fitted in studies of moderate air pollution and episode studies.

Air Pollutants↗

PubMed1992

Effects of ambient ozone on respiratory function and symptoms in Mexico City schoolchildren.

The effects of ambient ozone (O3) on respiratory function and acute respiratory symptoms were evaluated in 143 7- to 9-yr-old schoolchildren followed longitudinally at 1- to 2-wk intervals over a period of 6 months at three schools in Pedregal, Mexico City. The maximum O3 level exceeded the World Health Organization guideline of 80 ppb and the U.S. standard of 120 ppb in every week. For an increase from lowest to highest in the mean O3 level during the 48 hr before spirometry (53 ppb), logistic regression estimated relative odds of 1.7 for a child reporting cough/phlegm on the day of spirometry. For the full population, the mean O3 level during the hour before spirometry, not adjusted for temperature and humidity, predicted a significant decrement in FVC but not in FEV1 or FEF25-75. In contrast, the mean O3 level during the previous 24-, 48-, and 168-h periods predicted significant decrements in FEV1 and FEF25-75 but not in FVC. Ozone was consistently associated with a greater decrement in lung function for the 15 children with chronic phlegm as compared with the children without chronic cough, chronic phlegm, or wheeze. Ozone in the previous 24-, 48-, and 168-h periods predicted decrements in FEV1 for children of mothers who were current or former smokers, but not for children of mothers who were never smokers. Many of these effects were reduced in multiple regression analyses including temperature and humidity, as temperature and O3 were highly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗

PubMed1991

Daily diaries of respiratory symptoms and air pollution: methodological issues and results.

Daily diaries of respiratory symptoms are a powerful technique for detecting acute effects of air pollution exposure. While conceptually simple, these diary studies can be difficult to analyze. The daily symptom rates are highly correlated, even after adjustment for covariates, and this lack of independence must be considered in the analysis. Possible approaches include the use of incidence instead of prevalence rates and autoregressive models. Heterogeneity among subjects also induces dependencies in the data. These can be addressed by stratification and by two-stage models such as those developed by Korn and Whittemore. These approaches have been applied to two data sets: a cohort of school children participating in the Harvard Six Cities Study and a cohort of student nurses in Los Angeles. Both data sets provide evidence of autocorrelation and heterogeneity. Controlling for autocorrelation corrects the precision estimates, and because diary data are usually positively autocorrelated, this leads to larger variance estimates. Controlling for heterogeneity among subjects appears to increase the effect sizes for air pollution exposure. Preliminary results indicate associations between sulfur dioxide and cough incidence in children and between nitrogen dioxide and phlegm incidence in student nurses.

Air Pollution↗

PubMed1991

Sensitive subgroups and normal variation in pulmonary function response to air pollution episodes.

The Clean Air Act requires that sensitive subgroups of exposed populations be protected from adverse health effects of air pollution exposure. Hence, data suggesting the existence of sensitive subgroups can have an important impact on regulatory decisions. Some investigators have interpreted differences among individuals in observed pulmonary function response to air pollution episodes as evidence that individuals differ in their sensitivity. An alternative explanation is that the differences are due entirely to normal variation in repeated pulmonary function measurements. This paper investigates this question by reanalyzing data from three studies of children exposed to air pollution episodes to determine whether the observed variability in pulmonary function response indicates differences in sensitivity or natural interoccasion variability. One study investigated exposures to total suspended particulates (TSP), the other two investigated exposure to ozone. In all studies, each child's response to air pollution exposures was summarized by regressing that child's set of pulmonary function measurements on the air pollution concentrations on the day or days before measurement. The within-child and between-child variances of these slopes were used to test the hypothesis of variable sensitivity. Regression slopes did not vary significantly among children exposed to episodes of high TSP concentration, but there was evidence of heterogeneity in both studies of ozone exposures. The finding of heterogeneous response to ozone exposure is consistent with the epidemiologic and chamber studies of ozone exposures, but the lack of evidence for heterogeneous response to TSP exposures implies that observed variation in response can be explained by sampling variability rather than the presence of sensitive subgroup.

Air Pollution↗

PubMed1979

Effects of sulfur oxides and respirable particles on human health. Methodology and demography of populations in study.

As part of a study of health effects of sulfur dioxide and particulate matter, we have established a cohort of adults 25 to 74 yr of age in 6 communities who will be followed prospectively. At the conclusion of our first cycle of measuring the health of adults in 6 sites we found that, although we used different sampling frames, our samples were close to the distribution shown in the U.S. Census for age, sex, and occupation, with the possible exception of one city. Analysis of the cross-sectional data indicated that for both age- and height-adjusted values for forced expiratory volume in 1 s and for selected rates of various respiratory symptoms standardized for age, differences among smoking groups were apparent. Differences in these parameters between sites suggest trends that were associated with levels of pollution. Further analyses of the prospective data currently being collected will be required before definitive statements can be made about the effect of specific levels of exposure.

Adult↗

PubMedDate not supplied

Role of exposure databases in epidemiology.

At present, exposure databases record data primarily for regulatory purposes; they have not focused on serving the needs of epidemiologists or public health. However, the modification of exposure databases could facilitate their use in epidemiology. Characteristics necessary to enhance the use of all databases include easy access by users; documentation of methods, sampling bias, error, and inconsistences; widespread coverage in time and space; and methods and measures for estimating exposure of individuals as well as populations. Also needed are exposure scenarios and models to estimate exposures for geographic areas and time intervals not currently sampled. Multidisciplinary teams are needed to examine current databases, to review strategies for improving data collection, and to suggest and help implement appropriate changes. A long-term goal is to develop and validate data from exposure scenarios and models using data on the relationship of exposure to doses measured in humans.

Databases, Factual↗

PubMedDate not supplied

What makes a child allergic? Analysis of risk factors for allergic sensitization in preschool children from East and West Germany.

Earlier epidemiologic studies within Germany found a higher frequency of allergic sensitization in West Germany. The reasons for that and the role of environmental factors in the process of allergic sensitization are not fully understood. This study aimed to determine the prevalence of positive skin-prick test results 5 years after unification and to investigate risk factors for allergic sensitization in preschool children. A total of 1235 children (5-6 years) from two West and five East German locations were skin-prick tested after the compulsory school entrance examination. Six common aero- (birch, grass, mugwort pollen, cat, HDM, alternaria) and two food allergens (egg, milk) were used and additional information was obtained by questionnaire. Of the tested children 23.3% exhibited at least one positive reaction. The prevalence of sensitization to the single allergens was as follows: grass (14.4%), birch (6.6%), mugwort pollen (4.5%), cat (8.5%), HDM (5.5%), alternaria (4.9%), egg (2.8%), and milk (3.9%). In the crude analysis significantly more children were sensitized in the East German city Magdeburg (40.2%) compared to the West German control region Borken (23.5%) (OR 2.20, CI 1.47-3.29). Dampness and visible molds were reported in 8.8% of all households, but significantly more often for East German apartments (10.3% versus West Germany 1.9%, OR 5.85, CI 2.55-16.53). Dampness and molds were associated with a higher frequency of sensitizations (40.6% versus 27.6% in unaffected homes). After controlling for sex, parental atopy, SES, family size, and smoking during pregnancy, this association remained statistically significant (OR 1.93, CI 1.19-3.12). With regard to single allergens, dampness and visible molds were significantly associated with sensitization to HDM (OR 3.37, CI 1.63-6.96), cat (OR 3.19, CI 1.11-5.74), and mugwort pollen (OR 2.86, CI 1.29-6.35). In addition, family size was inversely and linearly associated with the frequency of sensitization (OR for four, three, and two-person households: 1.10 (0.74-1.63), 1.57 (1.06-2.42), 2.70 (1.39-5.24), respectively, when compared to family size of five or more). Neither parental predisposition for atopic diseases nor parental education level influenced the prick test reactivity. We conclude that in addition to genetic predisposition, environmental factors like indoor climate and probably infectious stimuli (family size) play an important role in the process of allergic sensitization in children.

Allergens↗