BMJ Open. Farm environment during infancy and lung function at age 31 Prospective birth cohort study in Finland

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1 Farm environment during infancy and lung function at age Prospective birth cohort study in Finland Journal: BMJ Open Manuscript ID: bmjopen Article Type: Research Date Submitted by the Author: 0-Dec-0 Complete List of Authors: Lampi, Jussi; National Institute for Health and Welfare, Department of Environmental Health; University of Eastern Finland, Public Health and Clinical Nutrition Koskela, Heikki; Kuopio University Hospital, Unit for Medicine and Clinical Research, department of respiratory medicine Hartikainen, Anna-Liisa; MRC of Oulu University, Department of Obstetrics and Gynecology of Oulu University Hospital Ramasamy, Adaikalavan; Imperial College London, Respiratory Epidemiology and Public Health; Imperial College London, Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health Couto Alves, Alexessander; Imperial College London, Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health Järvelin, Marjo-Riitta; Imperial College London, Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health; University of Oulu, Institute of Health Sciences Pekkanen, Juha; National Institute for Health and Welfare, Department of Environmental Health; University of Eastern Finland, Public Health and Clinical Nutrition <b>primary Subject Heading</b>: Secondary Subject Heading: Epidemiology Keywords: Occupational and environmental medicine EPIDEMIOLOGY, RESPIRATORY MEDICINE (see Thoracic Medicine), OCCUPATIONAL & INDUSTRIAL MEDICINE BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

2 Page of BMJ Open Farm environment during infancy and lung function at age Prospective birth cohort study in Finland Jussi Lampi a,b ; Heikki Koskela c ; Anna-Liisa Hartikainen d ; Adaikalavan Ramasamy e,f,g ; Alexessander Couto Alves f, Marjo-Riitta Järvelin f,h,i,j,k, Juha Pekkanen a,b. a Department of Environmental Health, National Institute for Health and Welfare, Kuopio, Finland. b Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland. c Center for Medicine and Clinical Research, Division of Pulmonary Medicine, Kuopio University Hospital, Kuopio, Finland d Department of Obstetrics and Gynecology of Oulu University Hospital,MRC of Oulu University, Oulu, Finland e Respiratory Epidemiology and Public Health, Imperial College London, UK f Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health, Imperial College London, UK g Department of Medical and Molecular Genetics, King s College London, UK h Institute of Health Sciences, University of Oulu, Oulu, Finland j Biocenter Oulu, University of Oulu, Oulu, Finland j Unit of Primary Care, Oulu University Hospital, Oulu, Finland k Department of Children and Young People and Families, National Institute for Health and Welfare, Oulu, Finland Address correspondence to: Jussi Lampi Department of Environmental Health BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

3 Page of National Institute for Health and Welfare P.O. Box, FI-00 Kuopio, Finland Telephone: jussi.lampi@thl.fi Keywords: Lung function, farming, longitudinal study Word Count: 0 BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

4 Page of BMJ Open ABSTRACT Objectives: Farming as occupation is considered as a risk factor for asthma and reduced lung function. In contrast, living on a farm during infancy has been reported to be associated with lower risk of asthma in adulthood. However, little is known about the association between farming environment during infancy and lung function in adulthood. We aimed to study prospective longitudinal association between farming environment during infancy and lung function in adulthood. Design: A prospective birth cohort study Setting: Northern Finland Participants: subjects born in were followed up at the age of. Primary outcome measures: Spirometry at the age of. Results: To be born into a farmer family was associated with higher FEV (forced expiratory volume in s) ( ml; % confidence interval (CI) to ml) and FVC (forced vital capacity) (0 ml; % CI to ml) at age. Contact with farm animals during infancy was associated with higher FEV. No associations were seen with FEV% (FEV/FVC ratio). Having dogs in childhood revealed similar associations. There was a suggestive dose-dependent association with number of animal species during childhood and higher FEV and FVC at adulthood, especially among women. Conclusions: Farming environment in early life may have a positive impact on lung function in adulthood. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

5 Page of Abbreviations: CI = confidence interval FEV = forced expiratory volume in s FEV% = FEV/FVC ratio FVC = forced vital capacity Strengths and limitations of the study The prospective nature of the study allowed analysis of longitudinal associations between farming environment during infancy and lung function at age without possible recall bias. The information was comprehensive about the factors in infancy which may affect lung function, including birth weight and pregnancy information. Though work and home based exposure to cold, dust, solvents, tobacco, as well as occupation at the age of was taken into account, detailed post-childhood information about farming exposures lacked. Due to lack of information about physical activity during childhood, its effect on the lung function at age cannot be estimated. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

6 Page of BMJ Open INTRODUCTION Farming environment during infancy, especially contact to the farm animals, is associated with decreased risk of asthma and allergic diseases -. Microbial exposure on a farm during infancy may inhibit the development of the allergic phenotype by influencing the development of the immune system. On the other hand, respiratory diseases such as asthma, allergic rhinitis, organic dust syndrome and extrinsic allergic alveolitis are well known occupational health problems among farmers. In farming environment, especially with farm animals, constant exposure to dusts (organic and inorganic), chemicals (e.g. pesticides and fertilizers), gases, fumes and infectious agents may irritate and induce inflammation in respiratory system,, lead to lung function impairment - and be a risk factor for respiratory diseases, e.g. asthma -. Therefore, living in farm environment during infancy may reduce the risk of asthma and allergic diseases in adulthood, whereas exposure during adulthood may be a risk factor for respiratory diseases. There is a lack of longitudinal studies on the effect of farming environment during infancy and lung function in adulthood. The present prospective birth cohort study, with detailed questionnaire data regarding infancy and childhood environment, offered an excellent opportunity to investigate the effect of farming environment in infancy, especially farm animal contact, on lung function measured by spirometry, at the age of years. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

7 Page of METHODS The Northern Finland Birth Cohort (NFBC) is a prospective study of 0 live births from the two northernmost provinces of Finland, Oulu and Lapland, and covered % of the children born in that region between January and December,. In, survivors still living in Northern Finland or in the capital city area received a postal questionnaire and invitation to clinical examinations, 00 attended the examinations. The University of Oulu Ethics Committee approved the study and the participants gave written informed consent. Antenatal and childhood factors Information about farming environment, lifestyle factors, maternal factors and socio-demographic factors in infancy was collected during pregnancy and/or immediately after delivery from the mother. Parental professional farming was defined if subject s mother, father or both were classified as professional farmers. Childhood information about having farm animals (species and counts), place of residence, residential density, maternal education, maternal age, maternal BMI, smoking during pregnancy from the second month, mother s age of menarche and parity number, gestational age at birth, birth weight and height were collected during pregnancy and/or immediately after delivery. Residential density was defined as number of subjects in household divided by number of rooms in household. Data obtained from hospital discharge registry was used to identify subjects with pneumonia before age of. Information about smoking at age was collected with questionnaires sent to participants and parents in 0. Assessment at age years During follow-up at age years, participants underwent a clinical examination, spirometry, skin prick tests, and filled in a health questionnaire. Lung function was assessed by FVC and FEV using a BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

8 Page of BMJ Open Vitalograph P-model spirometer (Vitalograph Ltd, Buckingham, UK) with a volumetric accuracy of % or 0ml, whichever was greater. The spirometer was calibrated regularly using -litre precision syringe. The spirometric manoeuvre was performed three times but was repeated if the difference between two maximal readings for FEV or FVC was >%. The highest FEV and FVC were used. The subjects in skin prick test with a mean weal reaction mm to one or more of the four allergens tested were considered to be atopic. Subjects with a positive reaction to the negative control or negative reaction to histamine (< mm) were excluded. At -year follow-up, participants also filled in questionnaires which included questions on health and lifestyle factors, ownership of a cat or a dog before the age of (retrospectively) and socio-demographic factors. Doctor-diagnosed asthma ever at the age of was based on self-report Statistical analyses The final analyses included those subjects who had complete spirometry data and were not pregnant. Multivariate linear models were used to analyze associations between farm environment, potential confounders and lung function. We identified a priori the list of potential confounders. At age potential confounders were height, weight, physical activity, education, smoking, exposure to cold, dust, solvents and tobacco smoke at work/or at home, paternal asthma, maternal asthma, paternal allergy and maternal allergy. Potential childhood confounders were height, weight and gestational age at birth, residential density, pneumonia before age of seven and smoking at age. Potential maternal confounders were mother s menarcheal age, parity number, age, education and smoking during pregnancy (after the second month of pregnancy). For the final models, we included all variables (see table ), which were associated with outcome at p<0. level and which changed the estimate for the gender adjusted association between farm animal during infancy and outcome (FVC, FEV) by more than 0%. Models for FEV were adjusted for gender, height at age, weight at age, smoking at BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

9 Page of age, education at age, exposure to the solvents and tobacco smoke at home at age, physical activity age, smoking at age, birth height and weight, maternal education, paternal asthma and maternal age. Models for FVC were adjusted for gender, height at age, weight at age, smoking at age, education at age, exposure to the solvents and tobacco smoke at home at age, physical activity age, birth height and weight, maternal education and residential density during infancy. Models for FEV% were adjusted with confounders selected for models for both FEV and FVC. Among included subjects, the maximum percentage of missing data for diseases was. %, for farm characteristics collected during mother s pregnancy 0. %, for pet ownership collected at the -year follow-up. % and for data on current occupation was. %. For statistical analyses, missing data for confounders were classified as its own category. The highest percentage of missing information concerned allergic conditions of father (. %). All analyses were conducted with IBM SPSS. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

10 Page of BMJ Open RESULTS Characteristics and overall prevalence s of allergic and respiratory diseases among study population at age are described in table. Having a parent who was a professional farmer during infancy was significantly associated with increased FEV and FVC at age (table ). Furthermore, having farm animals during infancy was associated with significantly increased FEV at age (table ). Having dogs in childhood revealed similar associations (table ). No associations were detected with FEV% (table ). There was a suggestive association between number of animal species during childhood and increasing lung function at age (table ), especially among women (table ). Further adjustment for current farming occupation at age had no impact to the size of the estimates of the observed significant associations on table (data not shown). Although associations between farming environment and higher lung function at age were most evident among women, no significant gender interactions (p < 0.0) were observed. The smallest p-value was observed for the interaction between gender and having cats in childhood (FVC, p = 0.0). Other p-values for interaction between gender and having dogs in childhood, having farm animals or professional farming during infancy ranged between p = 0. and p = 0.. To explore if the associations in table are mediated via the protective effect of childhood farming on atopy or asthma, the models were further adjusted for atopy and asthma (table ). Atopy and doctordiagnosed asthma reduced the size of the estimates in table by 0% at the most. This suggests that although atopy and asthma probably mediates the effect on improved lung function also other pathways are likely to be operational. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

11 Page 0 of Table. Characteristics of the study population at the age of, stratified by parental professional farming during infancy. Parental professional farming during infancy No Yes Measured characteristics n Mean n Mean FVC ( l).. FEV (l).. FEV% (%).0. Height (cm). 0. Weight ( kg).. General charasteristics# n % n % Female.. Current smoking High-school graduate 0.. Atopy*. 0. DD asthma.. # Study population n=; DD asthma n=; Atopy n= * Subjects with a weal reaction mm to one or more of the four allergens tested were considered to be atopic DD = doctor diagnosed ever BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

12 Page of BMJ Open Table. Associations between farming environment during infancy and lung function at the age of. FEV difference (ml) FVC difference (ml) Farm-related factors during infancy N Crude Adj. % CI Crude Adj. % CI Parental professional farming No Yes ( to ) 0 ( to ) Family had farm animals Family had dogs Family had cats No Yes ( to ) (- to ) No Yes (0 to ) ( to ) No Yes 0 (- to ) (- to ) Number of animal species# Number of cows # Includes cows, pigs, sheep, poultry, minks, cats and dogs Before the age of Crude: adjusted for gender and height at age ( to ) ( to ) 0 ( to ) 0 (- to ) (0 to 0) (0 to 0) or more (- to ) (- to 00) (- to ) (-0 to ) or more (- to ) (- to ) Adj.: multivariate model, for more detailed information see methods. on December 0 by guest. Protected by copyright. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from

13 Page of Table. Associations between farming environment during infancy and lung function at age stratified by gender. Women Men FEV difference(ml) FVC difference(ml) FEV difference (ml) FVC difference (ml) Farm related factors in infancy N Adj. (% Cl) Adj. (% Cl) N Adj. (% Cl) Adj. (% Cl) Parental professional farming No 0 (ref.) Yes ( to ) (- to ) (- to ) (- to 00) Family had farm animals Family had dogs Family had cats No Yes ( to ) (- to ) (- to ) - (- to ) No Yes (0 to ) ( to ) (- to 0) (- to ) No Yes 0 ( to ) 0 ( to ) 0 (- to ) -0 (- to ) Number of animal species# Number of cows # Includes cows, pigs, sheep, poultry, minks, cats and dogs Before the age of Adj. multivariate model, for more detailed information see methods. on December 0 by guest. Protected by copyright ( to ) ( to ) (-0 to ) (- to ) (0 to 0) (0 to ) (- to 0) - (- to ) (0 to ) ( to ) (- to ) (- to 0) or more ( to ) ( to 0) 0 (- to ) (- to ) ( to ) (- to ) (- to ) (- to ) or more 0 ( to ) (- to ) 0 (- to ) - (- to ) BMJ Open: first published as 0./bmjopen on July 0. Downloaded from

14 Page of BMJ Open Table. To explore if the statistically significant associations in table are mediated via the protective effect of childhood farming on atopy and asthma, the models were further adjusted for atopy and asthma. FEV Difference (ml) FVC Difference (ml) Farm-related factors during infancy Adj. Adj.+ A Adj.+ A + DDA Adj. Adj.+ A Adj.+ A + DDA Parental professional farming 0 Family had farm animals - Family had dogs 0 Before the age of Adj. multivariate model, for more detailed information see methods. A: also adjusted for atopy at the age of ; DDA: also adjusted for doctor-diagnosed asthma ever at the age of BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

15 Page of DISCUSSION To our knowledge, this is the first prospective birth cohort study on the association between farming environment during infancy and lung function at adult age. The results suggest that farming environment during infancy is associated with higher FEV and FVC at age. No associations with FEV% were observed. Our findings suggest that farming environment in early life may have a positive impact on lung function in adulthood. Respiratory diseases are well known occupational health problem among farmers. Lowered lung function has been reported among farmers in occupational setting,, and especially among farm animal workers in longitudinal studies, 0. Furthermore, Eduard at al. reported reduced FEV among livestock farmers compared to crop farmers, however with no association with FVC. Environmental exposure to the animal houses has also been reported to be associated with decreased FEV. On the other hand, Omland et al. reported that there were no associations between occupational farming and lung function with similar findings being described between dairy farmers and controls in a longitudinal study.the effect of early life farming environment on lung function is less clear. Merchant et al. reported that the children born in farm had higher FVC compared to children not born in a farm. However, most studies have reported that living on a farm in childhood has no effect on lung function on childhood, or adulthood. There is lack of prospective longitudinal studies on the matter. In contrast, numerous reports have been published in past decade concerning association between farming environment during infancy and decreased risk of allergic diseases and asthma -.It has been hypothesized that high microbial exposure in farming environment may affect development of the immune system during childhood and promote non-allergic phenotype. Some studies have reported that high microbial exposure, like exposure to bacterial endotoxin (Gram-negative bacterial cell wall BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

16 Page of BMJ Open component), may affect to the development of the immune system, 0 and lead to reduced risk of asthma in childhood,,. On the other hand, high endotoxin exposure may also irritate the airways and be a source of airway inflammation and obstruction not only in the occupational setting, but also during the infancy when endotoxin exposure may be a risk factor for wheezing. So, microbial exposure during infancy may promote development of non-allergic phenotype and decrease risk of allergic diseases and asthma, but it may also be a risk factor for occupational asthma and other occupational respiratory diseases such as organic dust syndrome and chronic bronchitis. In the present study farming environment during infancy was associated with higher FEV and FVC but not with FEV%. These spirometric findings suggest restrictive type lung function impairment among subjects without contact to the farming environment during infancy. This is an unexpected finding, since farming environment is mainly associated with obstructive disorders. However, as our lung function measurements consisted of FEV and FVC, type of the lung function impairment cannot be definitely identified. One potential mechanism for the present restrictive type findings may be obstruction in small airways caused by patchy collapse in early exhalation. In such case FEV and FVC are decreased and FEV% is normal. However, the possible contribution of airway obstruction on the suspected restrictive-type impairment would require a bronchodilator test. Confirmation of a true restrictive abnormality would require total lung capacity (TLC) measurement either with a body plethysmograph or gas dilution methods. We have previously shown in this cohort that early farming environment is associated with reduced risk of atopic sensitization, asthma and atopic diseases at the age of years. These associations are therefore potential explanations for the present observations. However, when we in additional analyses further adjusted for atopy and doctor-diagnosed asthma, the size of the estimates for the association BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

17 Page of between early childhood farming environment and current lung function were reduced by 0% at the most. This suggests that although atopy and asthma probably mediates the effect on improved lung function also other pathways are likely to be operational. These results suggest that early farming environment may not only prevent from development of atopy and asthma, but may also improve lung function in all exposed subjects. Differences in physical activity could also explain the observed differences in lung function. Physical activity is shown to be associated with higher lung function, measured with FEV in adulthood, with both men and women in all ages. In the present study, analyzes were adjusted for current, but not for childhood physical activity. It is possible that children living on farms during childhood have higher physical activity, as they may participate more in physically demanding tasks on farms, as compared to their peers living in non-farming environments. Unfortunately, there is lack of information about physical activity levels during childhood and therefore the effect of childhood physical activity on the lung function at age cannot be estimated. As the differences in subject s current or birth weight, as previously shown in this same setting, would offer simple explanation for current findings we adjusted all the models with both current and birth weight. We also run the models adjusting for body mass index at age instead of weight at age, but the results were unchanged. Therefore the associations between farming environment during infancy and lung function at adulthood are unlikely to be explained by obesity In general, there may be gender differences in respiratory responses to different environmental exposures. In a recent meta-analysis a higher risk of asthma was observed among women exposed to organic and inorganic dusts as compared to men. In contrast, exposure to organic dust was associated BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

18 Page of BMJ Open with lower lung function in men compared to women. In the present study, the observed associations were more evident among women, but this difference between genders did not quite reach nominal statistical significance. These gender differences may be due to differences in biology or in exposure patterns, e.g. in Finland, women and girls have traditionally taken care of cattle. As the present study was prospective by nature, we were able to analyse associations between farming environment during infancy and lung function at age without possible recall bias. Because the present study lacked detailed information on farm environment after infancy it was not possibly to conduct detailed assessments of the effect of farm environment at different time-points. However, in the analysis we have been able to take work and home based exposure to cold, dust, solvents and tobacco smoke at the age of account as well as current farming occupation. Furthermore, even in our prospective cohort study, possible healthy worker effect is always a concern. There was no suggestion at healthy worker effect in adulthood, as there was no change in the observed associations after adjustment for current farming occupation at age. However, it is possible that some parents of the present study subjects have avoided working in farm environment due to respiratory problems, which could lead to differences in the genetic predisposition between those living and those not living on a farm in infancy. However, this was less likely in Northern Finland in than it is today. In addition, in the statistical analyses parental history of allergies and asthma were adjusted for. Therefore, we consider health worker effect as an unlikely explanation for the present findings. CONCLUSIONS BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

19 Page of In conclusion, exposure to farming environment during infancy was associated with higher FVC and FEV, but not FEV%, at age. This suggests that farming environment in early life may have a positive impact on lung function in adulthood, but this needs to be confirmed in future studies. Acknowledgements We thank Professor Paula Rantakallio (launch of NFBC and initial data collection) and Mr Markku Koiranen (data management). Contributors Mr. Lampi wrote the manuscript and is the guarantor. He also performed statistically analysis and data interpretation and made substantial contributions to the planning of the manuscript. Mr. Koskela has made substantial contributions to the manuscript, statistically analysis, data interpretation and planning of the manuscript. Mrs. Hartikainen, Mr. Ramasamy, Mr. Couto Alves and Mrs. Järvelin have made substantial contributions to the manuscript and data interpretation. Mr. Pekkanen has made substantial contributions to the manuscript, to the planning of the manuscript, statistically analysis and data interpretation. All authors have critically revised and approved the final version of the manuscript. Funding Financial support was received from the Academy of Finland, Ministry of Health and Social Affair, the University of Oulu and from the University Hospital of Oulu. A.Ramasamy was supported through the European Commission (through project GABRIEL - contract #0 under the Integrated Program LSH ) and the Department of Health, UK. A. Couto Alves acknowledges the European Commission, Framework, grant number. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

20 Page of BMJ Open Competing Interests We declare that we have no conflict of interest. Ethical Approval The University of Oulu Ethics Committee approved the study and the participants gave written informed consent. Data sharing statement Not additional data is available BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

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24 Page of BMJ Open STROBE Statement checklist of items that should be included in reports of observational studies Item No Recommendation Title and abstract (a) Indicate the study s design with a commonly used term in the title or the abstract Introduction (b) Provide in the abstract an informative and balanced summary of what was done and what was found Background/rationale Explain the scientific background and rationale for the investigation being reported Objectives State specific objectives, including any prespecified hypotheses Methods Study design Present key elements of study design early in the paper Setting Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection Participants (a) Cohort study Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up Case-control study Give the eligibility criteria, and the sources and methods of case ascertainment and control selection. Give the rationale for the choice of cases and controls Cross-sectional study Give the eligibility criteria, and the sources and methods of selection of participants (b) Cohort study For matched studies, give matching criteria and number of exposed and unexposed Case-control study For matched studies, give matching criteria and the number of controls per case Variables Clearly define all outcomes, exposures, predictors, potential confounders, and effect Data sources/ measurement modifiers. Give diagnostic criteria, if applicable * For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group Bias Describe any efforts to address potential sources of bias Study size 0 Explain how the study size was arrived at Quantitative variables Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why Statistical methods (a) Describe all statistical methods, including those used to control for confounding Continued on next page (b) Describe any methods used to examine subgroups and interactions (c) Explain how missing data were addressed (d) Cohort study If applicable, explain how loss to follow-up was addressed Case-control study If applicable, explain how matching of cases and controls was addressed Cross-sectional study If applicable, describe analytical methods taking account of sampling strategy (e) Describe any sensitivity analyses BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

25 Page of Results Participants * (a) Report numbers of individuals at each stage of study eg numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analysed (b) Give reasons for non-participation at each stage (c) Consider use of a flow diagram Descriptive data * (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders (b) Indicate number of participants with missing data for each variable of interest (c) Cohort study Summarise follow-up time (eg, average and total amount) Outcome data * Cohort study Report numbers of outcome events or summary measures over time Case-control study Report numbers in each exposure category, or summary measures of exposure Cross-sectional study Report numbers of outcome events or summary measures Main results (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, % confidence interval). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were categorized (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period Other analyses Report other analyses done eg analyses of subgroups and interactions, and sensitivity analyses Discussion Key results Summarise key results with reference to study objectives Limitations Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias Interpretation 0 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence Generalisability Discuss the generalisability (external validity) of the study results Other information Funding Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based *Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies. Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at Annals of Internal Medicine at and Epidemiology at Information on the STROBE Initiative is available at BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

26 Farm environment during infancy and lung function at age Prospective birth cohort study in Finland Journal: BMJ Open Manuscript ID: bmjopen r Article Type: Research Date Submitted by the Author: -May-0 Complete List of Authors: Lampi, Jussi; National Institute for Health and Welfare, Department of Health Protection; University of Eastern Finland, Public Health and Clinical Nutrition Koskela, Heikki; Kuopio University Hospital, Unit for Medicine and Clinical Research, department of respiratory medicine Hartikainen, Anna-Liisa; MRC of Oulu University, Department of Obstetrics and Gynecology of Oulu University Hospital Ramasamy, Adaikalavan; Imperial College London, Respiratory Epidemiology and Public Health; Imperial College London, Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health Couto Alves, Alexessander; Imperial College London, Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health Järvelin, Marjo-Riitta; Imperial College London, Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health; University of Oulu, Institute of Health Sciences Pekkanen, Juha; National Institute for Health and Welfare, Department of Health Protection; University of Eastern Finland, Public Health and Clinical Nutrition <b>primary Subject Heading</b>: Secondary Subject Heading: Epidemiology Keywords: Occupational and environmental medicine EPIDEMIOLOGY, RESPIRATORY MEDICINE (see Thoracic Medicine), OCCUPATIONAL & INDUSTRIAL MEDICINE BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

27 Page of BMJ Open Farm environment during infancy and lung function at age Prospective birth cohort study in Finland Jussi Lampi a,b ; Heikki Koskela c ; Anna-Liisa Hartikainen d ; Adaikalavan Ramasamy e,f,g ; Alexessander Couto Alves f, Marjo-Riitta Järvelin f,h,i,j,k, Juha Pekkanen a,b. a Department of Health Protection, National Institute for Health and Welfare, Kuopio, Finland. b Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland. c Center for Medicine and Clinical Research, Division of Pulmonary Medicine, Kuopio University Hospital, Kuopio, Finland d Department of Obstetrics and Gynecology of Oulu University Hospital,MRC of Oulu University, Oulu, Finland e Respiratory Epidemiology and Public Health, Imperial College London, UK f Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health, Imperial College London, UK g Department of Medical and Molecular Genetics, King s College London, UK h Institute of Health Sciences, University of Oulu, Oulu, Finland j Biocenter Oulu, University of Oulu, Oulu, Finland j Unit of Primary Care, Oulu University Hospital, Oulu, Finland k Department of Children and Young People and Families, National Institute for Health and Welfare, Oulu, Finland Address correspondence to: Jussi Lampi Department of Health Protection BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

28 Page of National Institute for Health and Welfare P.O. Box, FI-00 Kuopio, Finland Telephone: jussi.lampi@thl.fi Keywords: Lung function, farming, longitudinal study Word Count: BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

29 Page of BMJ Open ABSTRACT Objectives: Farming as occupation is considered as a risk factor for asthma and reduced lung function. In contrast, living on a farm during infancy has been reported to be associated with lower risk of asthma in adulthood. However, little is known about the association between farming environment during infancy and lung function in adulthood. We aimed to study prospective longitudinal association between farming environment during infancy and lung function in adulthood. Design: A prospective birth cohort study Setting: Northern Finland Participants: subjects born in were followed up at the age of. Primary outcome measures: Spirometry at the age of. Results: To be born into a farmer family was associated with higher FEV (forced expiratory volume in s) ( ml; % confidence interval (CI) to ml) and FVC (forced vital capacity) (0 ml; % CI to ml) at age. Contact with farm animals during infancy was associated with higher FEV. No associations were seen with FEV /FVC (FEV /FVC ratio). Having dogs in childhood revealed similar associations. There was a suggestive dose-dependent association with number of animal species during childhood and higher FEV and FVC at adulthood, especially among women. Conclusions: Farming environment in early life may have a positive impact on lung function in adulthood. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

30 Page of Abbreviations: CI = confidence interval FEV = forced expiratory volume in s FEV /FVC = FEV/FVC ratio FVC = forced vital capacity Strengths and limitations of the study The prospective nature of the study allowed analysis of longitudinal associations between farming environment during infancy and lung function at age without possible recall bias. The information was comprehensive about the factors in infancy which may affect lung function, including birth weight and pregnancy information. Though work and home based exposure to cold, dust, solvents, tobacco, as well as occupation at the age of was taken into account, detailed post-childhood information about farming exposures lacked. Due to lack of information about physical activity during childhood, its effect on the lung function at age cannot be estimated. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

31 Page of BMJ Open INTRODUCTION Farming environment during infancy, especially contact to the farm animals, is associated with decreased risk of asthma and allergic diseases -. Microbial exposure on a farm during infancy may inhibit the development of the allergic phenotype by influencing the development of the immune system. On the other hand, respiratory diseases such as asthma, allergic rhinitis, organic dust syndrome and extrinsic allergic alveolitis are well known occupational health problems among farmers. In farming environment, especially with farm animals, constant exposure to dusts (organic and inorganic), chemicals (e.g. pesticides and fertilizers), gases, fumes and infectious agents may irritate and induce inflammation in respiratory system,, lead to lung function impairment - and be a risk factor for respiratory diseases, e.g. asthma -. Therefore, living in farm environment during infancy may reduce the risk of asthma and allergic diseases in adulthood, whereas exposure during adulthood may be a risk factor for respiratory diseases. There is a lack of longitudinal studies on the effect of farming environment during infancy and lung function in adulthood. The present prospective birth cohort study, with detailed questionnaire data regarding infancy and childhood environment, offered an excellent opportunity to investigate the effect of farming environment in infancy, especially farm animal contact, on lung function measured by spirometry, at the age of years. BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

32 Page of METHODS The Northern Finland Birth Cohort (NFBC) is a prospective study of 0 live births from the two northernmost provinces of Finland, Oulu and Lapland, and covered % of the children born in that region between January and December,. In, survivors still living in Northern Finland or in the capital city area received a postal questionnaire and invitation to clinical examinations. Detailed description about the number of participants and flow charts of the year follow-up study are shown in study website. The current analyses included those subjects who had complete spirometry data at the age of and were not pregnant. The University of Oulu Ethics Committee approved the study and the participants gave written informed consent. Antenatal and childhood factors Information about farming environment, lifestyle factors, maternal factors and socio-demographic factors in infancy was collected during pregnancy and/or immediately after delivery from the mother. Parental professional farming was defined if subject s mother, father or both were classified as professional farmers. Childhood information about having farm animals (species and counts), place of residence, residential density, maternal education, maternal age, maternal BMI, smoking during pregnancy from the second month, mother s age of menarche and parity number, gestational age at birth, birth weight and height were collected during pregnancy and/or immediately after delivery. Residential density was defined as number of subjects in household divided by number of rooms in household. Data obtained from hospital discharge registry was used to identify subjects with pneumonia before age of. Information about smoking at age was collected with questionnaires sent to participants and parents in 0. Assessment at age years BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.

33 Page of BMJ Open During follow-up at age years, participants underwent a clinical examination, spirometry, skin prick tests, and filled in a health questionnaire. Lung function was assessed by FVC and FEV using a Vitalograph P-model spirometer (Vitalograph Ltd, Buckingham, UK) with a volumetric accuracy of % or 0ml, whichever was greater. The spirometer was calibrated regularly using -litre precision syringe. The spirometric manoeuvre was performed three times but was repeated if the difference between two maximal readings for FEV or FVC was >%. The highest FEV and FVC were used. The subjects in skin prick test with a mean weal reaction mm to one or more of the four allergens tested were considered to be atopic. Subjects with a positive reaction to the negative control or negative reaction to histamine (< mm) were excluded. At -year follow-up, participants also filled in questionnaires which included questions on health and lifestyle factors, ownership of a cat or a dog before the age of (retrospectively) and socio-demographic factors. Doctor-diagnosed asthma ever at the age of was based on self-report Statistical analyses The final analyses included those subjects who had complete spirometry data and were not pregnant. Multivariate linear models were used to analyze associations between farm environment, potential confounders and lung function. We identified a priori the list of potential confounders. At age potential confounders were height, weight, physical activity, education, smoking, exposure to cold, dust, solvents and tobacco smoke at work/or at home, paternal asthma, maternal asthma, paternal allergy and maternal allergy. Potential childhood confounders were height, weight and gestational age at birth, residential density, pneumonia before age of seven and smoking at age. Potential maternal confounders were mother s menarcheal age, parity number, age, education and smoking during pregnancy (after the second month of pregnancy). For the final models, we included all variables (see table ), which were associated with outcome at p<0. level and which changed the estimate for the BMJ Open: first published as 0./bmjopen on July 0. Downloaded from on December 0 by guest. Protected by copyright.