Atopy: a predisposing factor for chronic bronchitis in Finland.

STUDY OBJECTIVE--To investigate the predictive value of atopy, smoking, and living in a farm environment in the development of chronic bronchitis. DESIGN--This was a cross sectional and longitudinal study. SETTING--Postal surveys carried out in Finland in 1975 and 1981. PARTICIPANTS--The study was part of the Finnish twin cohort study, which included adult twin pairs born in Finland before 1958. The cross sectional sample consisted of 18,351 subjects, including 1025 prevalent cases, and the follow up sample comprised 17,134 subjects, 553 of whom were incident cases of chronic bronchitis. MAIN RESULTS--According to the cross sectional data, chronic bronchitis was associated with atopy (relative risk 1.41) and smoking (2.43). In the follow up data, chronic bronchitis was related to atopy (1.28), smoking (2.31), and farming (1.45). CONCLUSIONS--The results confirm the earlier finding in the Finnish farming population that, in addition to smoking, atopy predisposes the development of chronic bronchitis. A farm environment was also found to be a predisposing factor. The results give further support to the "Dutch hypothesis" on the etiology of chronic bronchitis, according to which atopy is a predisposing factor.     

Acute lung function response to cotton dust in atopic and non-atopic individuals

Acute spirometric responses to inhaled cotton dust were examined in a population of 226 healthy, non-asthmatic adults whose atopic status had been evaluated by skin prick tests to 10 common environmental allergens. Exposure to cotton dust occurred in model cardrooms where elutriated dust levels were carefully controlled (1.02 mg/m3). Atopy, defined as positive prick tests to at least two allergens, was observed in 26% of subjects. Significant forced expiratory volume in one second (FEV1) decrements occurred after exposure to cotton dust independent of atopic status (p less than 0.001). The mean FEV1 decline in atopic subjects, however, was significantly greater than in non-atopic subjects (p less than 0.05). Degree of atopy, as measured by number of positive skin tests, also exhibited a significant association with cotton induced decrements in FEV1 (p less than 0.05). These data suggest that atopy may be an important determinant of the magnitude of the acute pulmonary response to cotton dust. This may reflect the non-specific airways hyperresponsiveness that has been described in non-asthmatic, atopic individuals.     

Acute lung function response to cotton dust in atopic and non-atopic individuals.

Acute spirometric responses to inhaled cotton dust were examined in a population of 226 healthy, non-asthmatic adults whose atopic status had been evaluated by skin prick tests to 10 common environmental allergens. Exposure to cotton dust occurred in model cardrooms where elutriated dust levels were carefully controlled (1.02 mg/m3). Atopy, defined as positive prick tests to at least two allergens, was observed in 26% of subjects. Significant forced expiratory volume in one second (FEV1) decrements occurred after exposure to cotton dust independent of atopic status (p less than 0.001). The mean FEV1 decline in atopic subjects, however, was significantly greater than in non-atopic subjects (p less than 0.05). Degree of atopy, as measured by number of positive skin tests, also exhibited a significant association with cotton induced decrements in FEV1 (p less than 0.05). These data suggest that atopy may be an important determinant of the magnitude of the acute pulmonary response to cotton dust. This may reflect the non-specific airways hyperresponsiveness that has been described in non-asthmatic, atopic individuals.     

Work-related respiratory disorders among Finnish farmers

Several research projects on work-related respiratory diseases have been conducted in Finland. One of the largest, "Farmers' Occupational Health Programme," was conducted by the Social Insurance Institution of Finland during 1973-1983 in cooperation with Kuopio Regional Institute of Occupational Health and the National Board of Health. The main objective of the program was to develop a model for occupational health services for farmers. As a part of the program, postal surveys were conducted in 1979 and 1982. The surveys allowed an analysis of both the prevalence and the mean annual incidence of asthma, farmer's lung, and chronic bronchitis as well as of background variables related to the diseases. More than every tenth farmer suffered from these respiratory diseases. The occurrence of chronic bronchitis (the most common disease) was, in general, related to farming types in which grain crops (including animal feeds) were handled. Chronic bronchitis was most prevalent among farmers who worked in piggeries, implying a combined effect of grain dusts, dusts of animal origin, and development of the disease. Atopy predisposed to and had an additive effect with smoking on chronic bronchitis.     

Combined effect of grain farming and smoking on lung function and the prevalence of chronic bronchitis

The combined effect of grain farming and smoking on lung function and the prevalence of chronic bronchitis was examined in 1633 residents 20 to 65 years of age from the town of Humboldt, Saskatchewan. Multiple multivariate analysis indicated that in women grain farming and smoking had a significant synergistic effect on the values of forced expired volume in one second/forced vital capacity (FEV1/FVC), mid-expiratory flow rate (MMFR), flow rate at 50% and 25% of total volume (Vmax50 and Vmax25) after adjustment for covariates including age and height. No other factors were found to change the results. The combined effect of grain farming and smoking on lung function was not statistically significant in men. The data also show that female non-smoking grain farmers had an identical prevalence of chronic bronchitis compared with non-smoking female non-farmers, 2.0% versus 2.1%. But in women with a positive smoking history, the prevalence was 13.2% and 5.9% respectively, giving an adjusted odds ratio in grain farmers compared to non-farmers of 3.55 (95% confidence interval (Cl): 1.06-11.30). It was found that the prevalence of chronic bronchitis increased more rapidly with increasing cigarette consumption in grain farmers than in non-farmers in women. It was estimated that 85%, 72% and 66% of the prevalence of chronic bronchitis was attributed to the joint effects of grain farming and ex-smoking, light smoking (1-19 cigarettes/day) or heavy smoking (20+ cigarettes/day) status, respectively. In contrast to women, the effect of grain farming on the prevalence of chronic bronchitis was similar in men with and without a positive smoking history. Our data suggest that there is a positive interactive effect of grain farming exposure and smoking on lung function and the prevalence of chronic bronchitis in women. The difference in the interaction between men and women requires further study.     

Ventilatory dysfunction in glass bangle workers

The pulmonary function status of 73 glass bangle workers suffering from chronic bronchitis having varied exposures to pulmonary toxicants in the work environment was evaluated in 1984. The findings were compared with those observed in 220 asymptomatic glass bangle workers and 88 unexposed controls. There was a higher prevalence (45.2%) of ventilatory dysfunction in the chronic bronchitic cases as compared to 19% in the asymptomatic workers and 2.3% in controls, respectively. The relative risk of airway obstruction was 8.3 and 19.6 times higher in the asymptomatic and chronic bronchitic workers respectively as compared to the controls (p less than 0.001). The prevalence of obstructive impairment among the smokers and non-smokers in the exposed workers was not statistically significant. However, age greater than 30 was found to be significantly associated with bronchial obstruction in chronic bronchitic cases. The relative risk of duration of exposure was found to be 1.86 in the asymptomatic workers exposed for more than 10 years (p less than 0.05) while it was 1.62 in workers with chronic bronchitis. The occupational and environmental factors responsible for the high prevalence of chronic bronchitis and associated ventilatory dysfunction in relatively young glass bangle workers are discussed.     

Gender differences in platelet count and its association with cigarette smoking in a large cohort in Israel.

Cigarette smoking has an effect on platelet function and aggregation although the sensitivity of platelet count in reflecting this phenomenon is not known. The association of platelet count with smoking habits was examined in a cohort of 5017 Israeli industrial workers aged 20-64 years. Males had a significantly lower age-adjusted mean platelet count than females (225,600 vs 247,800/microliters; p less than 0.001). Female smokers had lower platelet counts than non-smokers (231,000 for heavy vs 252,000 for never smokers) with a strong dose-response relationship (p less than 0.0001), whereas among males platelet count was slightly higher in smokers (224,000 for non-smokers vs 227,000 for heavy smokers; p = 0.243). The difference in platelet count between the sexes remained almost identical after controlling for smoking status and hematocrit. In multiple regression analysis, the negative association between smoking and platelet count in women remained highly significant (p less than 0.001) after controlling for ethnic origin, alcohol consumption, body mass, hematocrit, cholesterol and HDL-cholesterol, whereas for males the slight positive association was not significant. The reduced platelet count observed in males compared with females and in female smokers, suggests that platelet count may reflect sex differences in hemostasis and the effects of smoking on the hemostatic system. This may have implications for the mechanisms underlying the pathogenesis of ischemic heart disease and should be explored further.     

Respiratory symptoms in Swiss farmers: an epidemiological study of risk factors

BACKGROUND: The study was undertaken to assess the prevalence and risk factors of self-reported asthma, symptoms of chronic bronchitis, hay fever, and work-related respiratory symptoms in Swiss farmers as well as to compare the prevalence rates of respiratory symptoms with the Swiss population (SAPALDIA-Study). METHODS: An epidemiological study was performed with a representative sample of 1,542 Swiss farmers using a self-administered questionnaire. To investigate the effect of the type of farming on reported symptoms, the farmers were subdivided into seven groups according to the time farmers spent in different animal confinement buildings. A multivariate analysis was performed by the methods of binary and multivariate logistic regression adjusted for age and smoking habits. RESULTS: In farmers the prevalence rate was 16.0% for chronic bronchitis, 15.4% for asthma symptoms, and 42.0% for reporting at least one work-related symptom. Using logistic regression analysis, it was established that poultry farming and pig/cattle farming was a risk factor for reporting nasal irritation at work [OR 5.33, (1.57-18.0), OR 3.37 (1.04-10.87)]. Poultry farmers experienced the highest symptom rates. In crop farmers, the prevalence for chronic bronchitis was increased [OR 2.32 (1.03-5.23)]. Over 4 hr spent per day in animal confinement buildings more than doubled the risk for reporting chronic bronchitis [OR 2.61 (1.01-6.76)] and phlegm [OR 2.3 (0.99-5.4)] independent of the type of farming. The comparison of Swiss farmers with the Swiss population showed a twofold elevated risk of reporting chronic bronchitis [OR 1.89 (1.32-2.95)] and a 4.5-fold elevated risk for bringing up phlegm regularly [OR 4.5 (3.25-6.69)] in farmers. In contrast, the risk of farmers to report nasal allergies was less than half as high [OR 0.40 (0.29-0.56)] as that of the general population. CONCLUSIONS: This study shows that agricultural work in Switzerland is associated with an elevated risk for reporting symptoms of chronic bronchitis and chronic phlegm compared with the general Swiss population. These main results most likely indicate occupational disorders as the exposure-response relationship (hours spent in animal confinements) was particularly obvious for these symptoms.     

Work related distal airway obstruction in an agricultural population.

OBJECTIVE--To assess the prevalence of distal airway obstruction and its risk factors in agricultural areas. METHODS--A cross sectional study of respiratory symptoms and lung function was performed among French farmers and their spouses (1122 subjects) who came for preventive medicine examinations. They answered a respiratory questionnaire and performed pulmonary function tests on a portable spirometer. Diagnoses of chronic bronchitis were made on the basis of reported chronic respiratory symptoms. Airway obstruction was determined from predicted values. Odds ratio (OR) and linear regression coefficients were calculated after stratification by smoking and history of cardiac and other respiratory diseases. RESULTS--Of respiratory symptoms prevalence of chronic cough was 8.47%, and chronic bronchitis 7.66%. Prevalence of distal airway obstruction was 11.4%, and overall airflow obstruction 3.2%. Smokers were 20.2% men, and 5.7% women. Linear regressions showed high association between pack-years in smokers or exsmokers and forced expiratory volume in one second/forced vital capacity (FEV1/VC) and forced expiratory flow between 25% and 75% of vital capacity (FEF25-75). In non-smokers without any history of cardiac or respiratory diseases, age and the size of farms had the highest correlations with these variables. OR for distal airway obstruction was 2.1 in subjects > 50 years old v the younger ones and 3.02 in the smaller farms v the larger ones. CONCLUSION--After stratification by smoking and history of cardiac and respiratory diseases, distal airway obstruction is present in agricultural areas. The age, and the size of farm are the highest respiratory risk factors in non-smokers.     

Atopic and non-atopic asthma in a farming and a general population

BACKGROUND: In a previous study inverse associations between asthma and exposure to fungal spores and endotoxins in atopic farmers and positive associations with the same factors in non-atopic farmers were documented. No external reference population had been included. We, therefore, compared this farming population with the general population from an adjacent region. METHODS: Random samples of a farming (n=2,106) and a rural (n=351) and urban (n=727) general population were selected. Atopy was assessed by serum IgE and asthma by questionnaires. RESULTS: The asthma prevalence was 4.0% among farmers, 5.7% in the rural, and 7.6% in the urban population. Atopy was similar (9-10%). Most asthmatics were not atopic, 67-75%. Farmers had asthma less often than the general population OR 0.52 (95% CI 0.36-0.75); both atopic (OR 0.33 (95% CI 0.15-0.69)) and non-atopic asthma (OR 0.60 (95% CI 0.39-0.93)). CONCLUSION: This may indicate a protective effect of the farm environment on asthma but a healthy worker effect may also play a role.     

Chronic bronchitis: Prevalence, smoking habits, impact, and antismoking advice

Although the prevalence of chronic bronchitis has been measured in several populations, its impact on quality of life has not been assessed. We report the prevalence and impact of chronic bronchitis (defined as having phlegm on most days for at least 3 months during the previous year) among 4,708 adults ages 20 to 69 representative of the nonaged U.S. population. Men reported chronic bronchitis more frequently than women (12 vs 8%); smokers, regardless of age and sex, reported chronic bronchitis more frequently than former or never smokers. Among both men and women 35 years of age or older, current smokers--as opposed to ex- or never smokers--with chronic bronchitis had the poorest forced expiratory volume in 1 sec (FEV1). The most commonly reported impact of chronic bronchitis was worry, followed by pain and restricted activity days, regardless of age, sex, or smoking habits. Of those current and ex-smokers who had seen a physician about their chronic bronchitis, 65% of men and 44% of women had decreased or stopped smoking. Among those current and ex-smokers with chronic bronchitis who did not consult a physician, the proportion of those who had decreased or stopped smoking was 29% for men and 37% for women. Finally, only 43% of male current smokers and 55% of female current smokers who had chronic bronchitis reported that a physician had advised them to decrease or stop smoking.     

Somatotype, physical growth, and sexual maturation in young male smokers.

One thousand school boys aged 8 to 16 were examined for their somatotype, physical growth, sexual maturation, and smoking habits. Fifty-two boys were found to be smokers, of whom 30 were regularly smoking between two and 20 bidis or cigarettes a day for a mean duration of 2.5 years. The mean height and weight of the smokers was significantly lower than that of the non-smokers at all ages, more so in regular than occasional smokers. Sixty-nine per cent of the smokers had mesomorphic type of body build; about 65% of the non-smokers had ectomorphic somatotype (P less than 0.001). Onset of puberty occurred significantly earlier among smokers compared with non-smokers, as was evident from the early appearance of genital stage 2, and an early and rapid increase in testicular size. Genital stage 2 appeared at a mean age of 11 years in smokers and 11.6 years in non-smokers. However, the appearance of pubic, axillary, and facial hair was delayed. The possible significance of this is discussed.     

Dust exposure, pneumoconiosis, and mortality of coalminers

General mortality in approximately 25 000 British coalminers over 22 year periods ending in 1980 was 13% lower on average than in English and Welsh men in the same regions of Britain. There were significant within region variations between collieries, and standardised mortality ratios increased during the later years of the follow up, approaching or slightly exceeding 100 in most of the 20 coalmines studied. Age specific comparisons of 22 year survival rates were made in subgroups. Relative risks of death from all non-violent causes for men with the earliest stage of progressive massive fibrosis (PMF category A), compared with risks in miners with no pneumoconiosis (category O), ranged from 1.2 in those aged 55-64 initially to 3.5 for those aged 25-34. Mortality in miners with higher categories of PMF (B or C) was even more severe. Survival rates in men with category 1 simple pneumoconiosis were about 2% to 3% lower than in miners with radiographs classified as category O, but there was no consistent evidence of an increase in mortality with increasing category of simple pneumoconiosis. Mortality from all non-violent causes increased systematically with increases in estimates of exposure to dust before the start of the follow up. That gradient was attributable primarily to deaths certified as due to pneumoconiosis and those recorded as due to bronchitis and emphysema (p less than 0.001). There was some evidence of a dust related increase in deaths from cancers of the digestive system (p approximately equal to 0.05), but none of an association between exposure to coalmine dust and lung cancer. Lung cancer mortality, assessed over 17 year periods, was about 5.5 times higher in smokers than in life long non-smokers. Smokers with no pneumoconiosis had slightly higher lung cancer death rates than smokers with pneumoconiosis. We conclude that miners exposed to excessive amounts of respirable coalmine dust are at increased risk of premature death, either from progressive massive fibrosis or from chronic bronchitis or emphysema.     

Some social background variables among smoking and non-smoking primiparae

Of a population of 2,427 Norwegian primiparae, 62.7% were non-smokers, 23.0% smoked fewer than 10 cigarettes a day, and 14.3% smoked 10 or more a day. There was a significant correlation between smoking in pregnancy and age below 20 years, unmarried or previously married status, and poor education (p less than 0.001). Poor housing is of less importance. The mean age of smokers (24.0 years) was significantly lower than that of non-smokers (25.8 years) (p less than 0.001). The overall incidence of smoking in pregnancy was not significantly different from that in the normal population, but pregnant women under 20 smoked significantly more and those older than 24 significantly less, compared with their counterparts in a normal population (p less than 0.01).     

Dust exposure, pneumoconiosis, and mortality of coalminers.

General mortality in approximately 25 000 British coalminers over 22 year periods ending in 1980 was 13% lower on average than in English and Welsh men in the same regions of Britain. There were significant within region variations between collieries, and standardised mortality ratios increased during the later years of the follow up, approaching or slightly exceeding 100 in most of the 20 coalmines studied. Age specific comparisons of 22 year survival rates were made in subgroups. Relative risks of death from all non-violent causes for men with the earliest stage of progressive massive fibrosis (PMF category A), compared with risks in miners with no pneumoconiosis (category O), ranged from 1.2 in those aged 55-64 initially to 3.5 for those aged 25-34. Mortality in miners with higher categories of PMF (B or C) was even more severe. Survival rates in men with category 1 simple pneumoconiosis were about 2% to 3% lower than in miners with radiographs classified as category O, but there was no consistent evidence of an increase in mortality with increasing category of simple pneumoconiosis. Mortality from all non-violent causes increased systematically with increases in estimates of exposure to dust before the start of the follow up. That gradient was attributable primarily to deaths certified as due to pneumoconiosis and those recorded as due to bronchitis and emphysema (p less than 0.001). There was some evidence of a dust related increase in deaths from cancers of the digestive system (p approximately equal to 0.05), but none of an association between exposure to coalmine dust and lung cancer. Lung cancer mortality, assessed over 17 year periods, was about 5.5 times higher in smokers than in life long non-smokers. Smokers with no pneumoconiosis had slightly higher lung cancer death rates than smokers with pneumoconiosis. We conclude that miners exposed to excessive amounts of respirable coalmine dust are at increased risk of premature death, either from progressive massive fibrosis or from chronic bronchitis or emphysema.     

Relation between cotinine in the urine and indices based on self-declared smoking habits

Objectives The reliability of surveys on smoking habits based on questionnaires was investigated, using the urinary cotinine content as an objective index. Methods The subjects tested were 2,849 office workers of middle age, who responded to questions concerning their smoking status, and also their urinary cotinine was measured by the HPLC method. Results The boundary value between smokers and non-smokers, determined by the histogram independent of the questionnaire, was 63.1 and 79.4 ng/mg of creatinine for males and females, respectively. The rate of misclassification of the non-smokers and former smokers as smokers was 1.3% for males and 1.8% for females, whereas that of current smokers as non-smokers was 6.3% and 2.1%. We also assessed the effect of smoke inhalation on the urinary cotinine value, and found a significant difference for males in the cotinine value by the presence of inhalation and also its depth. Conclusions The rate of misclassification in this study was considered to be comparatively low. Several studies have also assessed the reliability of the questionnaire on smoking habits, and found different misclassification rates, indicating the dependence on the race and number of subjects tested. To our knowledge, there were only a few surveys on smoking among large groups, particularly in Japan, such as this one, therefore the results obtained in this study are meaningful.     

Smoking, adolescents and health: Isfahan healthy heart programme-heart health promotion from childhood

To evaluate the effect of some environmental factors on smoking, and to assess some health hazards of smoking in adolescents, this cross-sectional study was performed among 1950 students, agesll-18, selected by multi-stage random sampling from three cities in Iran. According to self-administered questionnaires, 12.9% of boys and 4% of girls reported to be smoker (OR = 3.34, 95% CI: 2.33, 4.77, p < 0.001). The mean values of total- and LDL-cholesterol were higher in smokers and their HDL-C was lower than non-smokers (163.33 +/- 33.83, 90.73 +/- 31 and 46.7 +/- 12.24 vs. 156 +/- 29.53, 85 +/- 26.5 and 49.4 +/- 13.7 mg/dl, respectively, p < 0.05). The mean systolic and diastolic blood pressures were higher in smokers than non-smokers (110.7 +/- 14.5, 67.6 +/- 11.55 vs. 104.9 +/- 14.3, 63.2 +/- 10.8 mmHg, respectively, p < 0.05). The smokers had higher BMI than non-smokers (20.34 +/- 3.84 vs. 19.55 +/- 3.66, p < 0.05). The mean food consumption frequency was lower for fruits and vegetables and higher for fat/salty snacks and fast foods in smokers than non-smokers. Logistic regression analysis showed significant association between sex, age, the number of family members and number of smokers in the family and smoking in students. The findings of this study have implications for future tobacco prevention strategies through community-based interventions.     

Prevalence and risk factors for chronic bronchitis and farmer''s lung in French dairy farmers.

The prevalence of chronic bronchitis and of clinical farmer's lung was studied in 30 districts of the French Doubs province in relation to individual (age, sex, smoking) and geographical (altitude) factors. 5703 exclusively dairy farmers (response rate 83%) participated in the study by answering a medical questionnaire. Prevalences of chronic bronchitis and clinical farmer's lung were 9.3% and 1.4% respectively. A logistic regression model was used to evaluate risk factors for chronic bronchitis and clinical farmer's lung. A risk of chronic bronchitis was associated with male sex (p < 10(-4)), age (p < 10(-4)), smoker category (p < 10(-4)), and altitude (p < 10(-4)). A risk of clinical farmer's lung was associated with non-smokers (p < 0.05), and linearly with altitude (p < 10(-4)). Also there was a strong positive relation between chronic bronchitis and clinical farmer's lung (odds ratio 19.5 (95% confidence interval 12.1-31.4) after adjustment for confounding variables. The main finding of this study is the highly significant increase of prevalence of the diseases in relation to altitude.     

Respiratory allergy in laboratory animal workers: a retrospective cohort study using pre-employment screening data.

OBJECTIVES: To study the role of exposure, atopy, and smoking in the development of laboratory animal allergy (LAA) in a retrospective cohort study. METHODS: Between 1977 and 1993, 225 people received a pre-employment screening when they started a job at a Dutch research institute where they were going to work with laboratory animals. After active follow up 136 of them (60.4%) could be traced and were sent a questionnaire with extensive questions on allergic symptoms, smoking habits, and job history. 122 people (89.7%) sent back a completed questionnaire. Those who were accepted for a job at the institute and did not have allergic symptoms at the start of the job were selected as cohort members. After selecting people with complete data on start and end date of jobs, exposure intensity, atopy, and smoking, the cohort consisted of 99 people with an average time of follow up of 9.7 years. LAA was defined as a positive response to a set of questions in the questionnaire. The mean number of hours a week a person was exposed to laboratory animals at entry of the cohort was used as a surrogate for exposure, and was divided into four categories. RESULTS: 19 cohort members (19.2%) reported LAA. More people with asthmatic symptoms were found in the high exposure categories. More atopic than non-atopic people reported asthmatic symptoms (13% v 6%). The mean time until development of symptoms of LAA was about 109 months in non-atopic people (n = 9), and 45 months in atopic people (n = 10) (t test; P < 0.05). Time until development of symptoms of LAA was shorter at a higher intensity of exposure, except for those exposed for less than two hours a week. A proportional hazard regression analysis showed that exposure and atopy were significant determinants of LAA. An increased relative risk (RR) was found for non-atopic people exposed to laboratory animal allergens for more than two hours a week. Atopic people had an even higher risk when exposed to laboratory animals for more than two hours a week (RR above 7.3). Sex, smoking, and age were not risk factors. More atopic than non-atopic people were absent from work or transferred because of allergies. CONCLUSIONS: This study showed that exposure and atopy are significant predictors of LAA and that the risk of developing LAA remained present for a much longer period (> 3 y) than considered before.     

Analyzing atopic and non-atopic asthma

There is a need to better define phenotypes of asthma. However, many studies have data available only on asthma and atopy, so they are often used to define ‘atopic’ and ‘non-atopic’ asthma. We discuss and illustrate the problems of analyzing such outcomes. We used the 31 year follow-up of the Northern Finland Birth Cohort 1966 (n=5,429). ‘Atopic asthma’ and ‘non-atopic asthma’ were defined based on presence or absence of atopy (any skin prick test ≥3 mm) at age 31. Gender and ownership of cat in childhood were used as risk factors. Simple calculations on hypothetical datasets were used to support the conclusions. ‘Atopic asthma’ and ‘non-atopic asthma’, are not well separated disease entities. The association of a risk factor with ‘atopic asthma’ and ‘non-atopic asthma’ is determined both by its association with asthma and with atopy. E.g. if a risk factor is not associated with asthma, but is protective for atopy, this will produce a protective association with ‘atopic asthma’, but an opposite association with ‘non-atopic asthma’. This is the result from the typical analysis, which uses all non-asthmatics as the comparison group. Valid results, unconfounded by atopy, can be gained by comparing asthmatics to nonasthmatics separately among atopics and non-atopics, i.e. by doing the analysis stratified by atopy. If data only on asthma and atopy are available, asthma and atopy should be analyzed at first as separate outcomes. If atopic and nonatopic asthma are used as additional outcomes, valid results can be gained by stratifying the analysis by atopy.