The association between alcohol consumption and risk of hip fracture differs by age and gender in Cohort of Norway: a NOREPOS study

The association between alcohol consumption and hip fracture differed by gender: Men aged 30-59 years drinking frequently or 14+ gl/week had higher risk than moderate drinkers. No significant association was seen in older men. Women not drinking alcohol had higher risk than those drinking moderately both regarding frequency and amount.

INTRODUCTION

We aimed to examine alcohol consumption and risk of hip fracture according to age and gender in the population-based Cohort of Norway (1994-2003).

METHODS

Socio-demographics, lifestyle, and health were self-reported and weight and height were measured in 70,568 men and 71,357 women ≥ 30 years. Information on subsequent hip fractures was retrieved from hospitals' electronic patient registries during 1994-2013. Frequency of alcohol consumption was categorized: never/seldom, moderate (≤ 2-3 times/week), or frequent (≥ 4 times/week), and amount as number of glasses per week: 0, 1-6, 7-13, 14-27, and 28+. Type of alcohol (wine vs. beer/hard liquor) was also examined. Cox's proportional hazards regression was used to estimate hazard ratios (HRs) stratified on gender and baseline age < 60 and ≥ 60 years.

RESULTS

During median 15-year follow-up, 1558 men and 2511 women suffered a hip fracture. Using moderate drinkers as reference, men < 60 years drinking frequently had multivariable adjusted HR = 1.73 (CI 1.02-2.96) for hip fracture and more than 2.5 times higher risk if they consumed 14+ glasses compared to 1-6 glasses per week. In other groups of age and gender, no statistically significant increased risk was found in those consuming the highest levels of alcohol. Compared to women with moderate or frequent alcohol use, never/seldom-drinking women had the highest fracture risk. In women, use of wine was associated with lower fracture risk than other types of alcohol.

CONCLUSIONS

Risk of hip fracture was highest in men < 60 years with the highest frequency and amount of alcohol consumption and in non-drinking women.

Prediction of gestational age based on genome-wide differentially methylated regions

Background

We explored the association between gestational age and cord blood DNA methylation at birth and whether DNA methylation could be effective in predicting gestational age due to limitations with the presently used methods. We used data from the Norwegian Mother and Child Birth Cohort study (MoBa) with Illumina HumanMethylation450 data measured for 1753 newborns in two batches: MoBa 1, n = 1068; and MoBa 2, n = 685. Gestational age was computed using both ultrasound and the last menstrual period. We evaluated associations between DNA methylation and gestational age and developed a statistical model for predicting gestational age using MoBa 1 for training and MoBa 2 for predictions. The prediction model was additionally used to compare ultrasound and last menstrual period-based gestational age predictions. Furthermore, both CpGs and associated genes detected in the training models were compared to those detected in a published prediction model for chronological age.

Results

There were 5474 CpGs associated with ultrasound gestational age after adjustment for a set of covariates, including estimated cell type proportions, and Bonferroni-correction for multiple testing. Our model predicted ultrasound gestational age more accurately than it predicted last menstrual period gestational age.

Conclusions

DNA methylation at birth appears to be a good predictor of gestational age. Ultrasound gestational age is more strongly associated with methylation than last menstrual period gestational age. The CpGs linked with our gestational age prediction model, and their associated genes, differed substantially from the corresponding CpGs and genes associated with a chronological age prediction model.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-016-1063-4) contains supplementary material, which is available to authorized users.

25-Hydroxyvitamin D in pregnancy and genome wide cord blood DNA methylation in two pregnancy cohorts (MoBa and ALSPAC)

The aim of the study was to investigate whether maternal mid-pregnancy 25-hydroxyvitamin D concentrations are associated with cord blood DNA methylation. DNA methylation was assessed using the Illumina HumanMethylation450 BeadChip, and maternal plasma 25-hydroxyvitamin D was measured in 819 mothers/newborn pairs participating in the Norwegian Mother and Child Cohort (MoBa) and 597 mothers/newborn pairs participating in the Avon Longitudinal Study of Parents and Children (ALSPAC). Across 473,731CpG DNA methylation sites in cord blood DNA, none were strongly associated with maternal 25-hydroxyvitamin D after adjusting for multiple tests (false discovery rate (FDR)>0.5; 473,731 tests). A meta-analysis of the results from both cohorts, using the Fisher method for combining p-values, also did not strengthen findings (FDR>0.2). Further exploration of a set of CpG sites in the proximity of four a priori defined candidate genes (CYP24A1, CYP27B1, CYP27A1 and CYP2R1) did not result in any associations with FDR<0.05 (56 tests). In this large genome wide assessment of the potential influence of maternal vitamin D status on DNA methylation, we did not find any convincing associations in 1416 newborns. If true associations do exist, their identification might require much larger consortium studies, expanded genomic coverage, investigation of alternative cell types or measurements of 25-hydroxyvitamin D at different gestational time points.

Motor development in children prenatally exposed to selective serotonin reuptake inhibitors: a large population-based pregnancy cohort study

OBJECTIVES

To estimate the association between prenatal exposure to selective serotonin reuptake inhibitors (SSRIs) and motor development in children considering the effect of maternal symptoms of anxiety and depression before, during and after pregnancy.

DESIGN

Population-based prospective pregnancy cohort study.

SETTING

The Norwegian Mother and Child Cohort study (MoBa) (1999-2008).

POPULATION

A total of 51 404 singleton pregnancies.

METHODS

Self-reported use of SSRIs was collected for the 6 months before pregnancy and prospectively during pregnancy. We used ordinal logistic regression as the statistical analysis.

MAIN OUTCOME MEASURES

Motor development was assessed by maternal reports of fine and gross motor development at child age 3 years by items from the Ages and Stages Questionnaire (ASQ). The maternal ASQ scores were compared with data from a MoBa sub-study where clinicians assessed motor development with the Gross and Fine Motor Mullen scales of early learning.

RESULTS

In all 381 women (0.7%) reported use of SSRIs during pregnancy, of these 159 reported on at least two questionnaires (prolonged use). Prolonged SSRI exposure was associated with a delay in fine motor development, odds ratio 1.42 (95% CI 1.07-1.87) compared with no SSRI exposure, after adjusting for symptoms of anxiety and depression before and during pregnancy. Severity of maternal depression seemed to explain the association only partially. Stratifying on depression after pregnancy had no impact on the estimated effect of SSRIs.

CONCLUSIONS

Prolonged prenatal exposure to SSRIs was weakly associated with a delayed motor development at age 3 years, but not to the extent that the delay was of clinical importance.

TWEETABLE ABSTRACT

Long-term prenatal SSRI exposure is weakly associated with delayed motor development independent of depression.

A multi-centre study of candidate genes for wheeze and allergy: the International Study of Asthma and Allergies in Childhood Phase 2

BACKGROUND

Common polymorphisms have been identified in genes suspected to play a role in asthma. We investigated their associations with wheeze and allergy in a case-control sample from Phase 2 of the International Study of Asthma and Allergies in Childhood.

METHODS

We compared 1105 wheezing and 3137 non-wheezing children aged 8-12 years from 17 study centres in 13 countries. Genotyping of 55 candidate single nucleotide polymorphisms (SNPs) in 14 genes was performed using the Sequenom System. Logistic regression models were fitted separately for each centre and each SNP. A combined per allele odds ratio and measures of heterogeneity between centres were derived by random effects meta-analysis.

RESULTS

Significant associations with wheeze in the past year were detected in only four genes (IL4R, TLR4, MS4A2, TLR9, P<0.05), with per allele odds ratios generally <1.3. Variants in IL4R and TLR4 were also related to allergen-specific IgE, while polymorphisms in FCER1B (MS4A2) and TLR9 were not. There were also highly significant associations (P<0.001) between SPINK5 variants and visible eczema (but not IgE levels) and between IL13 variants and total IgE. Heterogeneity of effects across centres was rare, despite differences in allele frequencies.

CONCLUSIONS

Despite the biological plausibility of IgE-related mechanisms in asthma, very few of the tested candidates showed evidence of association with both wheeze and increased IgE levels. We were unable to confirm associations of the positional candidates DPP10 and PHF11 with wheeze, although our study had ample power to detect the expected associations of IL13 variants with IgE and SPINK5 variants with eczema.

School air quality related to dry cough, rhinitis and nasal patency in children

Controls for indoor air quality (IAQ) in schools are not usually performed throughout Europe. The aim of this study was to assess the effects of IAQ on respiratory health of schoolchildren living in Norway, Sweden, Denmark, France and Italy. In the cross-sectional European Union-funded HESE (Health Effects of School Environment) Study, particulate matter with a 50% cut-off aerodynamic diameter of 10 microm (PM(10)) and CO(2) levels in a day of normal activity (full classroom) were related to wheezing, dry cough at night and rhinitis in 654 children (10 yrs) and to acoustic rhinometry in 193 children. Schoolchildren exposed to PM(10) >50 microg x m( -3) and CO(2) >1,000 ppm (standards for good IAQ) were 78% and 66%, respectively. All disorders were more prevalent in children from poorly ventilated classrooms. Schoolchildren exposed to CO(2) levels >1,000 ppm showed a significantly higher risk for dry cough (OR 2.99, 95% CI 1.65-5.44) and rhinitis (OR 2.07, 95% CI 1.14-3.73). By two-level (child, classroom) hierarchical analyses, CO(2) was significantly associated with dry cough (OR 1.06, 95% CI 1.00-1.13 per 100 ppm increment) and rhinitis (OR 1.06, 95% CI 1.00-1.11). Nasal patency was significantly lower in schoolchildren exposed to PM( 10) >50 microg x m(-3) than in those exposed to lower levels. A poor IAQ is frequent in European classrooms; it is related to respiratory disturbances and affects nasal patency.

Prenatal and postnatal parental smoking and acute otitis media in early childhood

AIM

To explore the associations between acute otitis media in early childhood and prenatal and postnatal tobacco smoke exposure.

METHODS

Subjects were 32 077 children born between 2000 and 2005 in the Norwegian Mother and Child Study with questionnaire data on tobacco smoke exposure and acute otitis media up to 18 months of age. Multivariate regression models were used to obtain adjusted relative risks for acute otitis media.

RESULTS

Acute otitis media was slightly more common in children exposed to parental smoking. The incidence from 0 to 6 months was 4.7% in unexposed children and 6.0% in children exposed both prenatally and postnatally. After adjusting for postnatal exposure and covariates, the relative risk for acute otitis media 0-6 months when exposed to maternal smoking in pregnancy was 1.34, 95% confidence interval: 1.06-1.69. Maternal smoking in pregnancy was associated with acute otitis media up to 12 months of age. Compared with non-exposed children, there was a slightly increased risk of recurrent acute otitis media for children exposed both prenatally and postnatally with a relative risk of 1.24, 95% confidence interval: 1.01-1.52.

CONCLUSION

Even in a cohort with relatively low exposure levels of parental smoking, maternal smoking in pregnancy was associated with an increased risk of acute otitis media in early childhood.

Effect of breastfeeding on asthma, lung function and bronchial hyperreactivity in ISAAC Phase II

The association between breastfeeding and wheezing, lung function and atopy was evaluated in the International Study of Asthma and Allergy in Childhood (ISAAC) Phase II. Cross-sectional studies were performed in 27 centres in 20 countries. Information on disease and exposure factors was collected by parental questionnaires. Data from 54,000 randomly selected school children (aged 8-12 yrs, 31,759 with skin prick testing) and a stratified subsample (n = 4,888) were used for testing the correlation of breastfeeding with bronchial hyperreactivity and lung function. Random effect models for meta-analysis were applied to calculate combined odds ratios (ORs). Any breastfeeding was associated with less wheeze both in affluent (adjusted OR (OR(adj)) 0.87, 95% confidence interval (CI) 0.78-0.97) and nonaffluent countries (OR(adj) 0.80, 95% CI 0.68-0.94). Further analyses revealed that this was true only for nonatopic wheeze in nonaffluent countries (OR(adj) 0.69, 95% CI 0.53-0.90). Breastfeeding was not associated with atopic wheeze and objective measures of allergy in both affluent and nonaffluent countries. In contrast, breastfeeding was associated with higher predicted forced expiratory volume in one second in affluent countries only (mean ratio 1.11, 95% CI 1.02-1.20). Breastfeeding is associated with protection against nonatopic wheeze, which becomes particularly evident in nonaffluent countries. Overall, breastfeeding was not related to any measure of allergy. These findings may explain some of the controversy regarding breastfeeding, since the direction of the association with breastfeeding depends on the predominating wheeze phenotype (e.g. atopic, nonatopic).

Changes in physical activity behavior and the development of body mass index during the last 30 years in Norway

Body mass index (BMI; kg/m(2)) has increased markedly in the last decades. We hypothesized that highly physically active persons both at work and at leisure would be resistant to weight gain. The hypothesis was tested by analyzing Norwegian cross-sectional data collected in the period 1972-2002. Participants were 214,449 men and 206,136 women (aged 20-70 years). During the last 30 years in men and the last 15 years in women, a systematic larger BMI increase per year was observed in the sedentary [regression coefficients (SE) in men 0.060 (0.004) kg/m(2) and women 0.137 (0.012) kg/m(2)] compared with highly physically active groups [regression coefficients (SE) in men 0.036 (0.00 4) kg/m(2), and in women -0.001 (0.039) kg/m(2)]. Analyses were robust to adjustments for age, smoking and education. There was a larger absolute net increase in the prevalence of obesity among the sedentary compared with persons performing light, moderate or heavy physical activity (PA) at leisure. PA level in women both at work and in leisure was not associated with weight gain during the last decades. This association was less evident among men. Men and women who were lightly, moderately or highly active at leisure were less likely to be obese compared with those who were sedentary.

Mould-specific immunoglobulin antibodies quantified by flow cytometry reflect mould exposure in Norwegian children

BACKGROUND

Studies from many countries have shown an association between dampness in buildings and airway symptoms. Little is known about the role of mould-specific IgG antibodies in this context. Objective To examine the IgG antibody response to mould applying a new flow cytometric assay, compare the results with the standardized ImmunoCap method, and evaluate the association of IgG to IgE antibodies, dampness in buildings, and airway symptoms like wheeze and asthma.

METHODS

A population of 3713 children 9-11 years of age living in Northern Norway was investigated for airway symptoms and dampness at homes by a parental questionnaire, using protocols of the International study of Asthma and Allergy in Childhood (ISAAC). Among these, a case-control study of 100 wheezers and 100 non-wheezers was established that included home inspection, a parental structured interview, and serum samples analysed for mould-specific IgG and IgE antibodies, total IgE, and specific IgE to an allergen panel (Phadiatop).

RESULTS

Self-reported visible signs of mould or moisture at home during the child's first year of life were a significant risk factor for both wheeze and asthma. The levels of mould-specific IgG antibodies were associated with mould and moisture findings, but only when IgG antibodies were measured by flow cytometry.

CONCLUSIONS

The results support that dampness at home can increase the risk of airway symptoms. IgG antibodies determined by flow cytometry reflect mould exposure better than antibodies measured by the conventional method. IgG antibodies measured by flow cytometry may be used as an indicator of mould exposure.

Residential outdoor air pollution and allergen sensitization in schoolchildren in Oslo, Norway

BACKGROUND

Epidemiological studies that have investigated the association between air pollution and atopy have found inconsistent results. Furthermore, often exposure to outdoor air pollution has had limited quality, and more individual exposure is needed.

OBJECTIVE

To investigate the relations between early and lifetime exposure to residential outdoor air pollution and allergen sensitization in 9-10-year-old children in Oslo, Norway.

METHODS

Sensitization to common allergens was measured by skin prick tests (SPTs), which were performed in 2244 children who had lived in Oslo since birth. Several definitions of positive SPT were used. Information on potential confounding variables was collected by a parental questionnaire. Exposure to outdoor air pollution was assessed by the EPISODE dispersion model, which calculates hourly concentrations of nitrogen dioxide (NO2), particulate matter (PM) with aerodynamic diameter <10 microm (PM10) and <2.5 microm (PM2.5), respectively.

RESULTS

We found no associations between long-term air pollution exposure and sensitization to any allergen, any indoor or any pollen allergen. However, lifetime air pollution exposure was associated with sensitization to the house dust mite Dermatophagoides farinae. One interquartile increase of lifetime exposure to NO2, PM10 and PM2.5 was associated with 1.88 (adjusted odds ratio) (1.02, 3.47) [95% confidence interval (CI)], 1.61 (0.96, 2.72) and 1.46 (0.96, 2.22), respectively, for D. farinae. Lifetime exposure was also associated with sensitization to cat in a subpopulation. Both associations diminished after adjusting for a contextual socio-economic factor.

CONCLUSION

Long-term exposure to traffic-related pollutants was generally not associated with allergen sensitization in 9-10-year-old Oslo children. However, lifetime exposure was associated with sensitization to D. farinae, and with sensitization to cat in a subpopulation, which may be explained by socio-economic confounding or multiple comparisons. The air pollution levels in Oslo may be too low to reveal associations with sensitization.

The Emerging Risk Factors Collaboration: analysis of individual data on lipid, inflammatory and other markers in over 1.1 million participants in 104 prospective studies of cardiovascular diseases

Many long-term prospective studies have reported on associations of cardiovascular diseases with circulating lipid markers and/or inflammatory markers. Studies have not, however, generally been designed to provide reliable estimates under different circumstances and to correct for within-person variability. The Emerging Risk Factors Collaboration has established a central database on over 1.1 million participants from 104 prospective population-based studies, in which subsets have information on lipid and inflammatory markers, other characteristics, as well as major cardiovascular morbidity and cause-specific mortality. Information on repeat measurements on relevant characteristics has been collected in approximately 340,000 participants to enable estimation of and correction for within-person variability. Re-analysis of individual data will yield up to approximately 69,000 incident fatal or nonfatal first ever major cardiovascular outcomes recorded during about 11.7 million person years at risk. The primary analyses will involve age-specific regression models in people without known baseline cardiovascular disease in relation to fatal or nonfatal first ever coronary heart disease outcomes. This initiative will characterize more precisely and in greater detail than has previously been possible the shape and strength of the age- and sex-specific associations of several lipid and inflammatory markers with incident coronary heart disease outcomes (and, secondarily, with other incident cardiovascular outcomes) under a wide range of circumstances. It will, therefore, help to determine to what extent such associations are independent from possible confounding factors and to what extent such markers (separately and in combination) provide incremental predictive value.

Association between level of physical activity and lung function among Norwegian men and women: the HUNT study

OBJECTIVE

To estimate the association between level of physical activity in 1984-1986 and 1995-1997 and lung function in 1995-1997 among Norwegian men and women aged 28-80 years.

DESIGN

In 1984-1986 and 1995-1997, all residents of Nord-Trøndelag County, Norway, aged > or =20 years were invited to participate in the Nord-Trøndelag Health Studies. These analyses included a sample that took part in both studies and underwent spirometry (n = 8047). We used linear regression models adjusting for potential confounders stratified by sex and age groups (28-49 years, 50-69 years and > or =70 years) to estimate the association between forced expiratory volume in 1 second (FEV1) and physical activity.

RESULTS

Men and women who were physically active in 1985 and 1995 had the highest lung function in both sexes and in all age groups. The reduction in FEV1 ranged from 20 ml to 170 ml, similar to 1-7% of predicted values dependent on physical activity level. Lung function was also associated with body mass index (BMI), height, smoking and subjective health.

CONCLUSIONS

The findings show that a high level of physical activity corresponds to about 3-5 years of normal decline in FEV1 (30 ml/year), and may therefore overcome the disadvantages of a decline in FEV1 from increasing age.

Genetic and environmental effects on exhaled nitric oxide and airway responsiveness in a population-based sample of twins

Elevated levels of exhaled nitric oxide (eNO) and airway hyperresponsiveness are intermediate phenotypes of asthma. Using population-based data collected from a sample of twins, the present authors estimated the relative contribution of genes, family environment and nonshared environmental influences to variations in eNO and airway responsiveness (AR). In addition, the genetic and environmental sources of covariation between these two asthma-related phenotypes were investigated. The study population comprised a random sample of 377 adult twins identified through the Norwegian Twin Registry. The main outcome variables were eNO and AR to methacholine. Genetic effects accounted for 60% of the variation in eNO. Family environment accounted for 30% of the variation in AR, while nonshared environmental influences explained the remaining variation for both measures. For both eNO and AR, there were significant regression effects for atopy and smoking. The small, but significant association between eNO and AR was primarily explained by genetic factors. Sub-analyses restricted to atopic and nonsmoking twins strengthened the observation. In conclusion, variations in exhaled nitric oxide and airway responsiveness appear to be explained by different genetic and environmental variance structures. Variation in exhaled nitric oxide is explained by genetic and nonshared environmental effects, whereas an environmental model best explains the variation in airway responsiveness. Common genetic effects explain the small but significant association between exhaled nitric oxide and airway responsiveness.

Cardiorespiratory fitness in relation to self-reported physical function in cancer patients after chemotherapy

AIM

The aim of this study was to estimate the association between objective cardiorespiratory fitness (CRF) and subjective self-reported physical function, taking into account the influence of mental distress. We hypothesized an association between these parameters, since they might be thought to measure parts of the same phenomenon.

METHODS

Approximately 1 month after discontinuation of all primary treatment, 90 cancer patients aged 18-50 years treated with chemotherapy were surveyed. CRF was determined by the Astrand-Ryhming indirect cycle ergometer test, which indicate peak VO2 in mL x kg(-1) x min(-1) (predicted VO2max). Self-reported physical function was assessed by The European Organisation for Research and Treatment of Cancer Core Quality of Life Questionnaire (EORTC QLQ-C30). The relation between VO2max and self-reported physical function was estimated by multiple linear regression. Mental distress (assessed by The Hospital Anxiety and Depression scale), age, gender, body mass index (BMI), time from treatment to physical test and diagnoses were included as potential confounders.

RESULTS

There was no association between predicted VO2max and self-reported physical function. Mental distress was negatively associated with self-reported physical function (P<0.001), but is not associated with predicted VO2max.

CONCLUSIONS

The results suggest that predicted VO2max does not reflect self-reported physical function and vice versa in cancer patients after chemotherapy. If information about cardiac and/or pulmonary status is required, direct or indirect measures of VO2max should be used.

Diverging prevalence trends of atopic disorders in Norwegian children. Results from three cross-sectional studies

BACKGROUND

During the last decades there has been extensive epidemiological research to explore the increasing prevalence of asthma and allergy in childhood. The worldwide variations in prevalence of these diseases necessitate regional rapports. Furthermore, time-trend analyses with comparable methods are important in order to monitor the rapidly changing prevalence of these diseases.

METHODS

Three cross-sectional questionnaire-based studies of asthma and allergy in schoolchildren were conducted in the counties of Troms and Finnmark, in northern Norway in 1985, 1995 and 2000. The two former studies included children from randomly selected primary schools (n = 1794/1985, n = 1432/1995). The latter study was a part of ISAAC-II Europe study (n = 3853). Identical items of asthma and allergy were employed. The analyses comprised only children 9-11 years of age.

RESULTS

The prevalence of asthma was 9.3, 13.2 and 13.8% in 1985, 1995 and 2000, respectively. However, great gender differences were detected; the prevalence of asthma increased in males from 1995 to 2000, from 14.1 to 17.0%, RR = 1.2 (95% CI 1.0-1.5), but decreased in females 1995 to 2000, from 12.3 to 10.5%, RR = 0.9 (95% CI 0.7-1.1). Furthermore, in children with asthma, a changing trend was found in the external factors that perceived symptoms, from typical allergens towards other, unspecific agents. The prevalence of self-reported atopic eczema/dermatitis syndrome (AEDS) was 13.4, 21.1 and 20.8% in 1985, 1995 and 2000, respectively. The prevalence of self-reported allergic rhinoconjunctivitis was in 16.5, 24.7 and 29.6% 1985, 1995 and 2000, respectively, RR (2000/1995) = 1.2 (95% CI 1.1-1.3).

CONCLUSION

The prevalence of asthma in girls has reached a plateau and even decreased from 1995 to 2000 which is in contrast to the asthma prevalence in boys that tends to continuously increase. The prevalence of AEDS which increased substantially between 1985 and 1995 did not change from 1995 to 2000. However, the prevalence of allergic rhinoconjunctivitis increased steadily from 1985, 1995 to 2000.

Baby swimming increases the risk of recurrent respiratory tract infections and otitis media

AIM

To estimate the association between baby swimming and recurrent respiratory tract infections and otitis media in the first year of life in children of parents without and with atopy.

METHODS

Norwegian schoolchildren (n = 2862) was enrolled in a cross-sectional study of asthma and allergy using the questionnaire of the International Study of Asthma and Allergies in Childhood (ISAAC). The outcomes were parental retrospective report of recurrent respiratory tract infections and otitis media diagnosed by a physician in the first year of life. The exposure was baby swimming during the same period. Parental atopy reflects a history of maternal or paternal asthma, hayfever or eczema.

RESULTS

The prevalence of recurrent respiratory tract infections was higher (12.3%) among children who took part in baby swimming than among those who did not (7.5%). The prevalence of recurrent respiratory tract infections during the first year of life was 5.6% and 10.5%, respectively, in children of parents without and with atopy, whereas the prevalence of baby swimming was 5.6% and 5.1%, respectively, in the two groups. Stratified analysis using parental atopy as strata showed that the increased risk of recurrent respiratory tract infections was only present among children of parents with atopy [adjusted odds ratio (aOR) 2.08, 95% confidence interval (95% CI) 1.08-4.031. A similar trend was present for otitis media (aOR 1.77, 95% CI 0.96-3.25).

CONCLUSION

The results of this study suggest that baby swimming and infant respiratory health may be linked. The findings need to be examined in a longitudinal study.

Airway infections in infancy and the presence of allergy and asthma in school age children

AIM

To investigate the association between a history of otitis media and respiratory tract infections in infancy and allergic sensitisation and asthma in school age children of atopic and non-atopic parents.

METHODS

Based on a survey of 4585 schoolchildren, three groups of children aged 6-16 years were selected, of whom 502 were eligible with complete data: (1) diagnosed asthma (n = 166); (2) wheeze within past 12 months (n = 155); and (3) no asthma/no wheeze (n = 181). This study population was further analyzed by subgroups of children with or without parental atopy. Main outcome measures were allergic sensitisation verified by skin prick test and asthma.

RESULTS

Children of atopic parents had a reduced risk of developing allergic sensitisation in school age if they had a combined history of both otitis media and lower respiratory tract infections during infancy (adjusted odds ratio (aOR) 0.13, 95% CI 0.03 to 0.50) or a history of otitis media (aOR 0.31, 95% CI 0.12 to 0.83). A history of lower respiratory tract infections in infancy increased the risk of asthma in children of non-atopic parents (aOR 4.21, 95% CI 1.68 to 10.57).

CONCLUSION

In the present study population, a history of otitis media in infancy seems to be negatively associated with allergic sensitisation in school age children of atopic parents, whereas a history of lower respiratory tract infections was positively associated with asthma in children of non-atopic parents.

The level of physical activity in long-term survivors of testicular cancer

The aim of this study was to estimate the level of physical activity (LPA) in a large cohort of testicular cancer survivors (TCSs) and compare these results with observations from men in the same age range in the general population (GenPop). We also wanted to identify parameters that influenced physical activity. The study populations consisted of 1276 TCSs treated with surgery, radiotherapy or chemotherapy with or without surgery (mean observation time was 12 years), and 20391 male inhabitants from a Norwegian county (GenPop). All completed a question investigating two sub-levels of physical activity. The logistic regression analysis adjusting for different covariates, showed significantly more physically active men among the TCSs compared with the GenPop (43 versus 37%) (adjusted odds ratio (aOR)=1.32 (95% Confidence Interval (CI) 1.10-1.58)). The results indicate that the experience of testicular cancer increases rather than reduces the LPA in TCSs, independent of treatment given.

Feasibility of measuring lung function in preschool children

BACKGROUND

There have been difficulties in applying spirometric tests to children of preschool age.

METHODS

The feasibility of measuring lung function was examined in 652 children aged 3-6 years using dynamic spirometry with an animation programme and the guidelines approved by the European Respiratory Society.

RESULTS

Data from 603 (92%) children with at least two acceptable forced expiratory manoeuvres were analysed; 408 (68%) achieved at least three acceptable manoeuvres. Children with only two acceptable manoeuvres were younger, shorter, and weighed less (p<0.001). The lower levels of lung function in this group were partly explained by body size. 63% of those with three acceptable manoeuvres had a difference of </=5% between the highest and second highest forced expiratory volume in 1 second (FEV(1)); when a difference of </=10% was applied, 91% of the children were included. A similar trend was seen for forced vital capacity (FVC). The acceptability and reproducibility increased with increasing age, and levels of lung function increased linearly with age. The linear regression model showed that standing height was a satisfactory predictor of lung function; the explained fraction of variance (R(2)) was 59% for FEV(1). Most FVC manoeuvres in children older than 3 years were acceptable and reproducible.

CONCLUSIONS

Spirometric testing is feasible in preschool children and may be useful for both clinical practice and research. This study may fill the deficiency in reference values for European preschool children.

The use of a feather quilt, childhood asthma and allergic rhinitis: a prospective cohort study

BACKGROUND

Feather bedding has long been considered as a potential source of allergen exposure and thus a potential risk factor for allergic diseases. However, recent cross-sectional studies have reported a higher risk of allergic diseases among users of synthetic bedding compared with feather-bedding users.

OBJECTIVE

To explore associations between early life exposure to feather bedding and the risk of developing asthma allergic rhinitis in childhood.

METHODS

We assessed the association between early life exposure to feather quilts and the risk of bronchial obstruction during the first 2 years of life and asthma and allergic rhinitis in a prospective 4-year cohort study of 2531 Norwegian children.

RESULTS

At the age of 6 months, 24% of the children had a quilt with feathers, decreasing to 20% at the age of 2 years. The adjusted odds ratio for bronchial obstruction 0 to 2 years by exposure to a feather quilt at the age of 6 months was 0.59, 95% confidence interval 0.41 to 0.86, for asthma at the age of 4 years 0.38, 0.23 to 0.64 and for allergic rhinitis at the age of 4 years 0.73, 0.43 to 1.18.

CONCLUSION

The use of a feather quilt in early life does not seem to increase the risk of asthma and allergic rhinitis later in childhood.

Physical activity affects the prevalence of reported wheeze

The present study examines whether physical activity level (hours per week) among children with and without asthma are associated with the prevalence of reported wheezing and whistling in the chest in the last 12 months. The data are based on a survey of school children, aged 7-16 years (n = 2188), in Oslo in 1994 that employed the ISAAC questionnaire. In children reporting asthma, wheezing and whistling in the chest in the last 12 months was less prevalent among inactive children (66.7%) compared to those who exercised (89.4%) (p = 0.05). The prevalence of wheeze also differed among inactive (4.4%) and active (8.8%) children not reporting asthma (p = 0.02). Positive associations between physical activity and wheezing and whistling in the chest remained present using multiple logistic regression analysis adjusting for sex, age and atopy. Children who are engaged in sports or exercise seem to report asthma symptoms differently than inactive children. These findings raise the question whether level of physical activity could affect some of the variability in reported asthma symptoms when such morbidity is measured as 'wheeze in last 12 months'.

Increased level of bronchial responsiveness in inactive children with asthma

We estimated the association between bronchial responsiveness and hours of exercise per week in children with and without asthma. A random sample of school children (n = 2188), 6-16 years old, was enrolled in a cross-sectional study of asthma in Oslo using the ISAAC questionnaire. Lung function and bronchial responsiveness (BR) using methacholine was measured in a random sample of 80 children with asthma, wheeze and no asthma/no wheeze. The relation between hours of exercise per week and BR [log (DRS)] was estimated by linear regression. Sex and age were included as covariates. Hours of exercise were categorized in: none, 30 min, 1 h, 2-3 h, 4-6 h and 7 h or more. The mean values of log (DRS) were different in the low and high exercise groups for children with asthma (P = 0.02), whereas there was no effect of exercise on BR for children without asthma. BR increased with decreasing hours of exercise per week in children with asthma. The bronchial responsiveness decreased with 0.11 (95% CI -0.20, -0.01) pr unit in scale. This pattern was not present in children without asthma. The results suggest that there is a relation between hours of exercise per week and bronchial responsiveness in children with asthma.

[Day care centers, infections and asthma]

BACKGROUND

Our objective was to use a causal model for childhood asthma to determine whether the effect of day care attendance on asthma was mediated by recurrent respiratory tract infections.

MATERIAL AND METHODS

The study is based on a cross-sectional survey among 1,447 children aged 6-16 years in Oslo. Their parents completed written questionnaires. A recursive logit model was used to estimate direct effects in terms of adjusted odds ratios (aOR).

RESULTS

Year of birth, number of siblings and length of maternal education were significantly associated with after-school care attendance. Attendance increased the risk of early infections, aOR = 1.8 (1.3-2.5), and infections were associated with asthma, aOR = 4.9 (3.4-7.3). The crude association between after-school care and asthma was cOR = 1.5 (1.0-2.2), whereas the estimated direct effect was small and non-significant, aOR = 1.2 (0.8-1.9). The results may be influenced by over-reporting of infections among parents with children with asthma.

INTERPRETATION

Our results suggest that children who attend day care have an increased risk of asthma, with early infections as a mediator of risk.

Asthma

From an epidemiological point of view four issues are briefly emphasized here: the definition of asthma, time trends and regional differences, and risk factors for asthma. Furthermore, I will focus upon a few aspects regarding the relation between exercise and asthma. The definition of asthma has presented problems for those involved in studying the disease in general populations, where the estimates rely solely on reported asthma and respiratory symptoms. A standardized questionnaire does not fully overcome differences in languages and interpretations of the concepts of asthma and wheeze over time and in different communities. Although the belief of an upward trend of childhood asthma seems to be widely accepted, studies with the proper methodology to investigate this issue are scarce. The prevalence of asthma varies within and between countries. There is no clear urban rural gradient, and the prevalence of atopy appears to be higher in western than in eastern Europe. Amazingly little is still known about genetic and environmental factors that are causally related to the manifestation of allergic disorders in previously asymptomatic individuals. The effect of exercise on asthma may be many-sided. Children with asthma can actively take part in sport. However, to what extent extensive exercise may affect the occurrence of bronchial responsiveness is unclear, and among athletes exercise may be a risk factor for the development of "athlete's asthma". In conclusion, epidemiological studies have to date not reached their potential due to the lack of longitudinal studies including objective measures of exposures and health outcomes. Causal inference is limited, and further studies designed to answer specific research questions are needed.

Daycare attendance, asthma and atopy

The objective of this article is to review studies that have examined the relation of daycare to asthma and atopy. In order to identify studies for inclusion, abstracts of all studies referenced in Medline from January 1966 to January 2000 and in BIBSYS were searched and extracted if they included 'asthma' or 'atopy' combined with words such as 'daycare', 'nursery' or 'kindergarten'. Eight studies fulfilled the criteria of inclusion. The outcomes were asthma, skin prick test (SPT) reactivity, a positive radioallergosorbent test (RAST), hay fever, and eczema. Daycare attendance was positively associated with asthma in five of six studies including asthma. In three of these studies there was no statistically significant association between daycare and asthma. Early start in daycare protected against later asthma in one study. There was a weak, but not a statistically significant positive relation between daycare and atopy in two of three studies when SPT reactivity was used as the outcome. In children of small families early start in daycare protected against atopy. The quality of the studies varies, and they are not directly comparable. The relation between daycare attendance and asthma and atopy is unclear, and further studies designed to answer this specific research question are needed.

The wheezing schoolchild--an undiagnosed asthmatic. A follow-up of children with parentally reported episodes of wheeze without diagnosed asthma

OBJECTIVE

To examine children aged 7-15 years with parentally reported episodes of wheeze in order to estimate the proportion of undiagnosed asthmatics in this group.

DESIGN

A cross-sectional study with clinical examination of subgroups.

SETTING

All children (n = 832) aged 7-15 years in the municipality of Odda.

SUBJECT

Based on completed questionnaires, the children were selected to one of four groups: Children with wheeze but no asthma (wheeze group); children with current asthma (asthma group); children with past asthma (past asthma group); and children with neither asthma nor wheeze (control group).

MAIN OUTCOME MEASURES

Parental reports of episodes of wheeze, assessment of skin prick test sensitivity, measures of lung function and exercise-induced bronchoconstriction (EIB).

RESULTS

In the wheeze group, 3 (7.5%) of 40 children were diagnosed with asthma in the 18-month period between the questionnaire survey and the examination, while 4 (10%) other children had EIB. Another 8 children (20%) reported 3 episodes of wheeze or more, and at least 1 episode during the 12-month period before the clinical examination. Classifying these children as asthmatics would give a proportion of 37.5% with undiagnosed asthma in the wheeze group, and the prevalence of current asthma among children aged 7-15 would rise from 2.9% based on a questionnaire survey to 4.9%. CONCLOSIONS: Using a wide definition of asthma, this study suggests that a large proportion of Norwegian children with wheeze actually have asthma.

Asthma and wheezing among Norwegian elite athletes

PURPOSE

The objectives were to estimate the prevalence of self-reports of asthma and wheezing among Norwegian elite athletes compared with the general population and to estimate the associations between asthma and types of sports, exercise and team level.

METHODS

The study population included all Norwegian elite athletes on the national junior and senior teams in 1997 (N = 1620) and a random sample from the general population (N = 1680). The surveys included items for asthma, respiratory symptoms, the history of participation in sports, sports events, and exercise and team level. The associations between the exposure variables and the outcomes adjusting for potential confounding factors were estimated using logistic regression. Crude (c) and adjusted odds ratio (aOR) with 95% confidence interval (CI) are presented.

RESULTS

The prevalence of asthma was greater among athletes (10.0%) compared with that in the general population (6.9%) and remained so after controlling for confounders, aOR = 1.5 (95%CI 1.1-2.1). The risk of asthma was highest in sports requiring strength and endurance. This was the case for comparisons between athletes and the general population, aOR = 3.5 (1.6-7.6) for strength and aOR = 2.2 (1.4-3.5) for endurance sports. Comparisons within the sample of athletes using technical sports as the reference category revealed similar results, aOR = 3.0 (1.1-8.0) and aOR = 2.0 (1.0-4.3), respectively. Furthermore, asthma was more common among female than male athletes (aOR 1.7 (1.1-2.7)). Training more than 20 h x wk(-1) was associated with asthma when compared with levels of training less than 10 h x wk(-1) (aOR 1.9 (1.0-4.1)).

CONCLUSION

These results indicate that asthma is more common among athletes compared with the general population. Asthma among athletes may define a subgroup of asthma cases for whom etiology is related to extensive exercise.

Asthma and allergy among schoolchildren in a mountainous, dry, non-polluted area in Norway

The aim of this study was to assess prevalence of asthma and allergy in the non-polluted mountain area of Upper Hallingdal, Norway. All schoolchildren (7-16 years) who in a previous questionnaire survey (n = 1177) reported 'sometime' asthma were enrolled in group I (n = 80), the 59 who reported asthma-like symptoms in the past 12 months formed group II, and 77 of the healthy controls were randomly selected as group III. All 216 children underwent clinical examination, skin prick test, spirometry, bronchial provocation (PD20 metacholine) and treadmill exercise test. Subsequently they were reclassified as (1) healthy, never had asthma or symptoms, (2) symptoms not confirmed as asthma, (3) previous asthma, now healthy, (4) current asthma. Lifetime asthma prevalence was 10.2%. Based upon clinical examination, the specificity and sensitivity of the questionnaire for asthma diagnosis were 88 and 74%, respectively. Forced vital capacity was significantly higher among the asthmatics (group 4 versus 1), whereas forced expiratory volume in one second (FEV1) and forced expiratory flow at 50% of vital capacity were similar in all groups. More than 10% reduction in FEV1 following treadmill-run was found in 20% of children. Children with current asthma compared to controls had significantly; lower mean values of PD20 (9.1 versus 16.5 micromol), higher eosinophil cationic protein (13.4 versus 7.7 micromol) and more frequent sensitization to animal dander (56% versus 10%). In conclusion, despite a favorable climate, little mite sensitization and low outdoor pollution, asthma prevalence was surprisingly high in Upper Hallingdal. Sensitization to animal dander was the most important contributing factor for current asthma.

A comparison of VO2(peak) between patients with congenital heart disease and healthy subjects, all aged 8-17 years

The peak oxygen uptake (VO2(peak)) of 196 healthy children and adolescents aged 8-16 years, and 187 children and adolescents (in the same age range) with congenital heart disease (CHD), was measured using a graded treadmill test (Oslo-protocol). The healthy population was tested to assess the reference values that were to be used in the interpretation of the results obtained from patients with CHD. The results revealed that patients with CHD exhibited lower VO2(peak) values, with declining values for boys after the age of 12-13 years. When separated into different diagnostic groups, on average, patients with a chronic pressure overload of the left ventricle and patients with tetralogy of Fallot have lower VO2(peak) values, but make approximately the same progress with age as healthy subjects. Patients with transposition of the great arteries, however, displayed a marked decline in VO2(peak) after the age of 12-13 years. Whether exercise testing should be included in routine follow-up in patients with CHD, especially those between the ages of 10 and 16 years, when the condition of some patients deteriorates, requires special attention.

Day care attendance, recurrent respiratory tract infections and asthma

OBJECTIVE

Our objective was to use a causal model for childhood asthma to determine whether the effect of day care attendance on asthma was mediated by recurrent respiratory tract infections.

DESIGN

A cross-sectional survey among 1447 children aged 6-16 years in Oslo. Their parents completed written questionnaires. A recursive logit model was used to estimate direct effects in terms of adjusted odds ratios (aOR).

RESULTS

Year of birth, number of siblings and length of maternal education were significantly associated with day care attendance. Attendance at day care increased the risk of early infections, aOR = 1.8 (1.3-2.5), and infections were associated with asthma, aOR = 4.9 (3.4-7.3). The crude association between day care and asthma was cOR = 1.5 (1.0-2.2), whereas the estimated direct effect was small and nonsignificant, aOR = 1.2 (0.8-1.9). The results may be influenced by overreporting of infections among parents of children with asthma.

CONCLUSIONS

Our results suggest that children who attend day care have an increased risk of asthma with early infections as a mediator of risk.

[What can twin research reveal about the causes of diseases?]

The purpose of this paper is to describe the place of twin studies in etiological research on somatic diseases, using asthma as an example. Twin studies provide answers to the relative importance of genes and environment in the development of disease, but have been criticised for systematic biases especially linked to unusual conditions in twin pregnancies. For asthma, classical twin studies show that genes explain the largest part of the interindividual variability, and that common family environment does not explain similarity in asthma in siblings. The assumptions underlying classical twin studies are discussed. A few other twin designs are mentioned, and we conclude that twin studies still play an important role in understanding causes of somatic diseases.

Wheezing in school children is not always asthma

Our objective was to study whether children with reported asthma differed from children with wheeze but without asthma, and from children with neither asthma nor wheeze, regarding lung function, bronchial hyper-responsiveness (BHR) using methacholine inhalation, exercise-induced bronchoconstriction (EIB), and skin prick test (SPT) reactivity. School children (n=2188), enrolled in a survey of asthma, were classified into three mutually exclusive groups by parental report of: asthma, wheeze, and no asthma/no wheeze. A random sample of 80 children in each group was tested (n=240). Among asthmatics, 68% (95% confidence interval (CI), 57-79) had a BHR (measured as PD20 forced expiratory volume in 1 s (FEV1) < or = 8.16 micromol using methacholine) compared to 31% (CI 20-42%) and 30% (CI 19-40%) in the wheeze and no asthma/no wheeze groups. The dose-response slope (DRS) confirmed the PD20 data and distinguished equally between groups. EIB (> or =10% fall in FEV1) was more frequent (40%, CI 29-52%) among asthmatics than among children with wheeze (12%, CI 4-19%) and no asthma/no wheeze (7%, CI 1-13%). The prevalence of at least one positive SPT was twice as high in the asthma group (58%, CI 47-69%) than in the wheeze (27%, CI 16-37%) and the no asthma/no wheeze (25%, CI 15-35%) groups. These results indicate that children with asthma differ from children with wheeze and children with no asthma/no wheeze regarding lung function, BHR, EIB, and SPT reactivity. Children with wheeze are more similar to children with no asthma/no wheeze with respect to these parameters.

Recurrent respiratory tract infections during the first 3 years of life and atopy at school age

BACKGROUND

The hypothesis that infections reduce the risk of atopy was investigated by estimating the association between recurrent respiratory tract infections during the first 3 years of life and atopy at school age.

METHODS

According to surveys in three different areas of Norway, children were classified into three groups: asthma, wheeze without asthma (wheeze), and no asthma/no wheeze. The skin prick test (SPT) was conducted on a stratified random sample of children (n = 502). The outcome was at least one positive SPT. The exposure variable was retrospective parental report of respiratory tract infections during the first 3 years of life.

RESULTS

Infections were negatively associated with atopy, crude odds ratio (cOR) = 0.3, 95% confidence interval (95% CI) 0.1-0.7, in the asthma group. A similar association was present in children with wheeze cOR = 0.4 (95% CI 0.1-1.2). The number of siblings was not associated with atopy in any group. Infections remained negatively associated with atopy in children with asthma, aOR = 0.3 (95% CI 0.1-0.7), in a logistic regression model adjusting for confounding factors. A similar pattern was present in the wheeze group.

CONCLUSIONS

Recurrent respiratory tract infections during the first 3 years of life are negatively associated with atopy at school age in children with asthma.

[Aerobic capacity in children and adolescents--Nordic results over the past 45 years]

The aim of this study was to reveal whether today's children and adolescents have lower aerobic capacity compared with earlier studies. Aerobic capacity may be defined as the highest amount of oxygen a subject is able to consume per unit of time. Peak oxygen uptake (VO2peak) is often used as a measure of aerobic capacity in children. VO2peak in 196 healthy children and adolescents of both sexes, aged 8-16 years, was measured on a graded treadmill test. The mean results of VO2peak (l.min-1) showed only small differences compared with previous studies in Scandinavia. There was, however, greater dispersion in the present study when the VO2peak-values were corrected for weight (ml.kg-1.min-1) than in the earlier studies. When compared to other countries in Europe, Norwegian subjects achieved higher values. The reason may be due to either genetic differences or to a higher level of physical activity among the Norwegian subjects.

Aerobic endurance testing of children and adolescents--a comparison of two treadmill-protocols

Fifty-eight children and adolescents of both sexes, aged 8-16, were tested on a treadmill using two different protocols. The well-known Bruce-protocol has the disadvantages of steep incline and large increments at each step. A new protocol (Oslo-protocol) with less incline and smaller increments was compared to the Bruce-protocol. The results from the two protocols showed no differences with regard to peak oxygen uptake (VO2peak) or peak heart rate (HRpeak). However, the respiratory exchange ratio (R) and blood lactate concentration [La-] showed higher values when the Bruce-protocol was used. The study also indicated that the often used criteria of HRpeak, R and achievement of a plateau in VO2 to estimate VO2peak, were not reliable indicators in either protocol. When time to exhaustion was used as an estimation of aerobic endurance level, the Oslo-protocol discriminated better than the Bruce-protocol. As a conclusion, the results indicate that none of the criteria may be used as a reliable indicator of having achieved VO2peak. An experienced testleader may be essential to define when VO2peak has been reached in children. On the basis of the results from the current study, the Oslo-protocol seems suitable as a test-protocol when testing children and adolescents for VO2peak.

Increasing risk of asthma without other atopic diseases in school children: a repeated cross-sectional study after 13 years

Some children develop asthma and other atopic diseases, others asthma without atopic diseases. To better understand secular trends, we estimated the relative increase in asthma in children with (atopy related asthma) and without (non-atopy related asthma) other atopic diseases (eczema or hay fever) in two samples of school children born, 1965-1975 (n = 1674) and 1978-1988 (n = 2188). By analysing the samples as historical cohorts, age-specific prevalence rates were estimated and incidence rates were calculated (number of new cases by 1000 person years under risk). Cox regression was used to estimate the relative risk (RR) of asthma by year of birth. The point prevalence of asthma was 1.9% (95% CI: 1.4-2.4) in the 1965-1975 cohort and 4.6% (95% CI: 3.8-5.4) in the 1978-1988 cohort for three-year old children, and remained fairly constant throughout childhood. The age-specific prevalence of non-atopy related asthma increased relatively more from 1965-1975 to 1978-1988 compared to atopy related asthma. The age-specific incidence rates of asthma showed that the RRs comparing the two cohorts tended at all ages to be highest for non-atopy related asthma. The relative risks of non-atopy related asthma by gender and birth cohort, showed that the effect of cohort was higher for non-atopy related asthma, aRR: 4.0 (95 % CI: 2.5-6.5), than for atopy-related asthma aRR: 2.0 (95% CI: 1.3-3.2). Children without other atopic diseases have a higher relative risk of being diagnosed with asthma than children with other atopic diseases across all ages comparing two samples of school children born 1965-1975 and 1978-1988.

The physical activity level in children with asthma based on a survey among 7-16 year old school children

The objective was to compare the physical activity level of children with asthma with that of non-asthmatic children. A standardized written questionnaire was administered in a survey of school children in three different areas of Norway: Oslo (n = 2577), Hallingdal (n = 831) and Odda (n = 1177). Response rates were > 85% in all areas, and approximately 50% of the respondents were female. No significant differences were found between the distributions in exercise frequency either for children reported ever to have had asthma (P = 0.8) or for those with current asthma (P = 0.3) compared to non-asthmatics. Similar results were found for exercise hours a week. More than 50% of all children took part in organized sport. The data suggest that asthmatic children are as physically active as their peers.

Changing prevalence of asthma in school children: evidence for diagnostic changes in asthma in two surveys 13 yrs apart

It is still unclear whether the reported increase in the prevalence of asthma is real or due to changes in diagnostic criteria. The objectives of this study were to compare the prevalence of diagnosed asthma with the prevalence of respiratory symptoms, and to compare the association between asthma and other atopic diseases in 1981 and 1994. The study populations comprised randomly selected school classes in Oslo in 1981 (n=1,772) and 1994 (n=2,577). The main outcomes in these comparable cross-sectional studies of children, 6-16 yrs of age, were parent-reported prevalence of diagnosed asthma, respiratory symptoms, eczema and hay fever. The questionnaire was identical in 1981 and 1994. The response rates were 94% (1,674 out of 1,772) in 1981 and 85% (2,188 out of 2,577) in 1994. The lifetime prevalence of asthma increased from 3.4% in 1981 to 9.3% in 1994; odds ratio (OR) 2.9 (95% confidence interval (95% CI) 2.1-4.0) comparing 1994 to 1981. The prevalence of occasional wheezing increased from 9.0 to 10.8%; OR 1.2 (95% CI 1.0-1.5), and attacks of wheezing from 3.7 to 6.8%; OR 1.8 (95% CI 1.3-2.5). Survival analyses for 3 year birth cohorts showed that asthma was more readily diagnosed in the latest birth cohort (1985-1988). The association between asthma and other atopic diseases decreased during the period under study. The increase in diagnosed asthma and respiratory symptoms supports a true increase in asthma. However, the larger increase in diagnosed asthma than wheezing and a reduced association between asthma and other atopic diseases suggest that the increase in asthma may be explained, in part, by changes in diagnostic criteria.

[Occurrence of asthma among school children in Norway during the period 1985-94]

Several comparable surveys of childhood as have been performed in Norway. This article describes the prevalence among children, 6-13 years old, during the period 1985-94, and how this prevalence is influenced by the operational definition of asthma. Questionnaires were administered in eight areas; Troms/Finnmark (1985), Nordland (1985), Ardal/Laerdal (1989/92), Sør-Varanger (1992), Oslo (1994), Hallingdal (1994) and Odda (1994). The response rates varied from 85 to 96%. The parent-reported lifetime prevalences were lowest in the areas where the studies took place in 1985, the earliest year of study; Nordland 7.2% (95% CI 6.5-7.9), Troms/Finnmark 8.1% (7.4-8.8). The prevalence increased up to 1994, with the highest prevalence in Oslo 13.7% (12.0-15.4). The prevalence of current asthma was about half the lifetime prevalence; Oslo 5.7% (4.6-6.8) compared with 10.1% (8.5-11.6). When respiratory symptoms the estimates were doubled in some areas and regional differences were reduced. The prevalence increased during the study period and seemed to be highest in northern Norway. Regions classified as polluted did not have a higher prevalence.

The prevalence of respiratory symptoms and asthma among school children in three different areas of Norway

The role of exposure to ambient air pollution has been a topic of interest as a potential risk factor for respiratory symptoms and asthma. We expected that the prevalence rates would vary in Norway between the capital, Oslo, the mountainous area Hallingdal and the industrial area Odda. Surveys were conducted in school children, aged 6-16 years, in; Oslo (n = 2577), Hallingdal (n = 1177) and Odda (n = 831). The parent-reported prevalence of wheeze in past year was almost similar in Oslo (13.1 (95% CI 11.7-14.5)) and Upper Hallingdal (14.2 (13.1-15.3)), but lower in Odda (9.0 (7.0-11.0)). The findings for severe respiratory symptoms were almost equal. The age patterns within each area differed. The risk of wheeze ever (p < 0.001) and wheeze in past year (p = 0.04) decreased with increasing age in Odda, while there was an increase in the risk of exercise induced wheeze in Oslo (p = 0.02) and Hallingdal (p < 0.001). The lifetime prevalence of asthma was lowest in Odda (5.4 (3.8-7.0)) compared to Oslo (9.4 (8.2-10.6)) and Hallingdal (8.5 (6.8-10.2)). There was a positive association between physical activity and wheeze in past year. The results do not support the hypothesis that respiratory morbidity is more common in urban than rural areas, age and physical activity can influence the prevalence rates of respiratory symptoms in school children.