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Flor LS, Anderson JA, Ahmad N, Aravkin A, Carr S, Dai X, Gil GF, Hay SI, Malloy MJ, McLaughlin SA, Mullany EC, Murray CJL, O'Connell EM, Okereke C, Sorensen RJD, Whisnant J, Zheng P, Gakidou E. Health effects associated with exposure to secondhand smoke: a Burden of Proof study. Nat Med 2024; 30:149-167. [PMID: 38195750 PMCID: PMC10803272 DOI: 10.1038/s41591-023-02743-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 11/28/2023] [Indexed: 01/11/2024]
Abstract
Despite a gradual decline in smoking rates over time, exposure to secondhand smoke (SHS) continues to cause harm to nonsmokers, who are disproportionately children and women living in low- and middle-income countries. We comprehensively reviewed the literature published by July 2022 concerning the adverse impacts of SHS exposure on nine health outcomes. Following, we quantified each exposure-response association accounting for various sources of uncertainty and evaluated the strength of the evidence supporting our analyses using the Burden of Proof Risk Function methodology. We found all nine health outcomes to be associated with SHS exposure. We conservatively estimated that SHS increases the risk of ischemic heart disease, stroke, type 2 diabetes and lung cancer by at least around 8%, 5%, 1% and 1%, respectively, with the evidence supporting these harmful associations rated as weak (two stars). The evidence supporting the harmful associations between SHS and otitis media, asthma, lower respiratory infections, breast cancer and chronic obstructive pulmonary disease was weaker (one star). Despite the weak underlying evidence for these associations, our results reinforce the harmful effects of SHS on health and the need to prioritize advancing efforts to reduce active and passive smoking through a combination of public health policies and education initiatives.
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Affiliation(s)
- Luisa S Flor
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA.
- Department of Health Metrics Sciences, School of Medicine, University of Washington, Seattle, WA, USA.
| | - Jason A Anderson
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Noah Ahmad
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Aleksandr Aravkin
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
- Department of Health Metrics Sciences, School of Medicine, University of Washington, Seattle, WA, USA
| | - Sinclair Carr
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Xiaochen Dai
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Gabriela F Gil
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
- Department of Global Health, University of Washington, Seattle, WA, USA
| | - Simon I Hay
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
- Department of Health Metrics Sciences, School of Medicine, University of Washington, Seattle, WA, USA
| | - Matthew J Malloy
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Susan A McLaughlin
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Erin C Mullany
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Christopher J L Murray
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
- Department of Health Metrics Sciences, School of Medicine, University of Washington, Seattle, WA, USA
| | - Erin M O'Connell
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Chukwuma Okereke
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Reed J D Sorensen
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Joanna Whisnant
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
| | - Peng Zheng
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
- Department of Health Metrics Sciences, School of Medicine, University of Washington, Seattle, WA, USA
| | - Emmanuela Gakidou
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
- Department of Health Metrics Sciences, School of Medicine, University of Washington, Seattle, WA, USA
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The Beneficial Effect of Farm Milk Consumption on Asthma, Allergies, and Infections: From Meta-Analysis of Evidence to Clinical Trial. THE JOURNAL OF ALLERGY AND CLINICAL IMMUNOLOGY-IN PRACTICE 2019; 8:878-889.e3. [PMID: 31770653 DOI: 10.1016/j.jaip.2019.11.017] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 11/18/2019] [Accepted: 11/18/2019] [Indexed: 12/23/2022]
Abstract
The low prevalence of asthma and allergies in farm children has partially been ascribed to the consumption of raw cow's milk. A literature search identified 12 publications on 8 pertinent studies. A meta-analysis corroborated the protective effect of raw milk consumption early in life (<1 to 5 years, according to study) on asthma (odds ratio [OR], 0.58; 95% CI, 0.49-0.69), current wheeze (OR, 0.66; 95% CI, 0.55-0.78), hay fever or allergic rhinitis (OR, 0.68; 95% CI, 0.57-0.82), and atopic sensitization (OR, 0.76; 95% CI, 0.62-0.95). The effect particularly on asthma was observed not only in children raised on farms (OR, 0.62; 95% CI, 0.58-0.82) but also in children living in rural areas but not on a farm (OR, 0.60; 95% CI, 0.48-0.74). This demonstrates that the effect of farm milk consumption is independent of other farm exposures and that children not living on a farm can theoretically profit from this effect. Because of the minimal but real risk of life-threatening infections, however, consumption of raw milk and products thereof is strongly discouraged. Raw farm milk and industrially processed milk differ in many instances including removal of cellular components, manipulation of the fat fraction, and various degrees of heating. Preliminary evidence attributes the effect to heat-labile molecules and components residing in the fat fraction. The Milk Against Respiratory Tract Infections and Asthma (MARTHA) trial is currently testing the protective effect of microbiologically safe, minimally processed cow's milk against standard ultra-heat-treated milk in children from 6 months to 3 years with the primary outcome of an asthma diagnosis until age 5 years. If successful, this approach might provide a simple but effective prevention strategy.
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Keijzers G, Sweeny A, Crilly J, Good N, Cameron CM, Mihala G, Scott R, Scuffham PA. Parental-reported allergic disorders and emergency department presentations for allergy in the first five years of life; a longitudinal birth cohort. BMC Pediatr 2018; 18:169. [PMID: 29788917 PMCID: PMC5964731 DOI: 10.1186/s12887-018-1148-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 05/08/2018] [Indexed: 01/16/2023] Open
Abstract
Background To measure rates of parental-report of allergic disorders and ED presentations for allergic disorders in children, and to describe factors associated with either. Methods An existing cohort of 3404 children born between 2006 and 2011 (Environments for Healthy Living) with prospectively collected pre-natal, perinatal and follow-up data were linked to i) nationwide Medicare and pharmaceutical data and ii) Emergency Department (ED) data from four hospitals in Australia. Parental-reported allergy was assessed in those who returned follow-up questionnaires. ED presentation was defined as any presentation for a suite of allergic disorders, excluding asthma. Univariate analysis and multivariate logistic regression were used to descibe risk factors for both parental-reported allergy and ED presentation for an allergic disorder. Results The incidence of parental-reported child allergy at 1, 3 and 5 years of age was 7.8, 7.8 and 12.6%, respectively. Independent predictors of parental-report of allergy in multivariate analysis were parental-report of asthma (OR 2.2, 95% CI 1.4–3.4) or eczema (OR 4.3, 95% CI 3.1–6.1) and age > 6 months at introduction of solids (OR 1.3, 95% CI 1.0–1.7). Factors associated with ED presentations for allergy, which occurred in 3.6% of the cohort, were presence of maternal asthma (OR 2.3 95% CI:1.1, 4.9) and child born in spring (OR 1.7, 95% CI 1.1, 2.7). Conclusions More than 10% of children up to 5 years have a parental-reported allergic disorder, and 3.6% presented to ED. Parental-report of eczema and/or asthma and late introduction of solids were predictors of parental-report of allergy. Spring birth and maternal asthma were predictors for ED presentation for allergy. Electronic supplementary material The online version of this article (10.1186/s12887-018-1148-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Gerben Keijzers
- Department of Emergency Medicine, Gold Coast University Hospital, 1 Hospital Boulevard, Southport, QLD, 4215, Australia. .,School of Medicine, Bond University, Gold Coast, QLD, Australia. .,School of Medicine, Griffith University, Gold Coast, QLD, Australia.
| | - Amy Sweeny
- Department of Emergency Medicine, Gold Coast University Hospital, 1 Hospital Boulevard, Southport, QLD, 4215, Australia
| | - Julia Crilly
- Department of Emergency Medicine, Gold Coast Health, Gold Coast, QLD, Australia.,Menzies Health Institute, Gold Coast, QLD, Australia
| | - Norm Good
- CSIRO Digitial Productivity/ Australian e-Health Research Centre, Royal Women's and Children's Hospital, Brisbane, QLD, Australia
| | - Cate M Cameron
- Jamieson Trauma Institute, Royal Brisbane & Women's Hospital, Metro North Hospital and Health Service, Herston, QLD, Australia.,Menzies Health Institute Queensland, Griffith University, Meadowbrook, QLD, Australia
| | - Gabor Mihala
- Menzies Health Institute Queensland, Griffith University, Nathan, QLD, Australia
| | - Rani Scott
- Menzies Health Institute Queensland, Griffith University, Meadowbrook, QLD, Australia
| | - Paul A Scuffham
- Menzies Health Institute Queensland, Griffith University, Nathan, QLD, Australia
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Orsi L, Magnani C, Petridou ET, Dockerty JD, Metayer C, Milne E, Bailey HD, Dessypris N, Kang AY, Wesseling C, Infante-Rivard C, Wünsch-Filho V, Mora AM, Spector LG, Clavel J. Living on a farm, contact with farm animals and pets, and childhood acute lymphoblastic leukemia: pooled and meta-analyses from the Childhood Leukemia International Consortium. Cancer Med 2018; 7:2665-2681. [PMID: 29663688 PMCID: PMC6010788 DOI: 10.1002/cam4.1466] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 12/27/2017] [Accepted: 02/20/2018] [Indexed: 12/11/2022] Open
Abstract
The associations between childhood acute lymphoblastic leukemia (ALL) and several factors related to early stimulation of the immune system, that is, farm residence and regular contacts with farm animals (livestock, poultry) or pets in early childhood, were investigated using data from 13 case-control studies participating in the Childhood Leukemia International Consortium. The sample included 7847 ALL cases and 11,667 controls aged 1-14 years. In all studies, the data were obtained from case and control parents using standardized questionnaires. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by unconditional logistic regression adjusted for age, sex, study, maternal education, and maternal age. Contact with livestock in the first year of life was inversely associated with ALL (OR = 0.65, 95% CI: 0.50, 0.85). Inverse associations were also observed for contact with dogs (OR = 0.92, 95% CI: 0.86, 0.99) and cats (OR = 0.87, 95% CI: 0.80, 0.94) in the first year of life. There was no evidence of a significant association with farm residence in the first year of life. The findings of these large pooled and meta-analyses add additional evidence to the hypothesis that regular contact with animals in early childhood is inversely associated with childhood ALL occurrence which is consistent with Greaves' delayed infection hypothesis.
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Affiliation(s)
- Laurent Orsi
- INSERM U1153, Epidemiology and Biostatistics Sorbonne Paris Cité Center (CRESS), Epidemiology of Childhood and Adolescent Cancers Team (EPICEA), Paris-Descartes University, Villejuif, France
| | - Corrado Magnani
- Dipartimento di Medicina Traslazionale, Università del Piemonte Orientale, AOUMaggiore della Carità & CPO, Piemonte, Novara, Italy
| | - Eleni T Petridou
- Department of Hygiene, Epidemiology, and Medical Statistics, School of Medicine, University of Athens, Athens, Greece.,Department of Medicine, Clinical Epidemiology Unit, Karolinska Institute, Stockholm, Sweden
| | - John D Dockerty
- Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | - Catherine Metayer
- School of Public Health, University of California, Berkeley, California
| | - Elizabeth Milne
- Telethon Kids Institute, University of Western Australia, Perth, Western Australia, Australia
| | - Helen D Bailey
- INSERM U1153, Epidemiology and Biostatistics Sorbonne Paris Cité Center (CRESS), Epidemiology of Childhood and Adolescent Cancers Team (EPICEA), Paris-Descartes University, Villejuif, France
| | - Nick Dessypris
- Department of Hygiene, Epidemiology, and Medical Statistics, School of Medicine, University of Athens, Athens, Greece
| | - Alice Y Kang
- School of Public Health, University of California, Berkeley, California
| | - Catharina Wesseling
- Unit of Occupational Medicine, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Claire Infante-Rivard
- Department of Epidemiology, Biostatistics, and Occupational Health, Faculty of Medicine, McGill University, Montréal, Quebec, Canada
| | | | - Ana M Mora
- Central American Institute for Studies on Toxic Substances (IRET), Universidad Nacional, Heredia, Costa Rica
| | - Logan G Spector
- Division of Epidemiology and Clinical Research, Department of Pediatrics and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota
| | - Jacqueline Clavel
- INSERM U1153, Epidemiology and Biostatistics Sorbonne Paris Cité Center (CRESS), Epidemiology of Childhood and Adolescent Cancers Team (EPICEA), Paris-Descartes University, Villejuif, France
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Ardura-Garcia C, Garner P, Cooper PJ. Is childhood wheeze and asthma in Latin America associated with poor hygiene and infection? A systematic review. BMJ Open Respir Res 2018. [PMID: 29531744 PMCID: PMC5844372 DOI: 10.1136/bmjresp-2017-000249] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Introduction High asthma prevalence in Latin-American cities is thought to be caused by poor hygiene and infections. This contradicts the widely accepted 'hygiene hypothesis' for asthma aetiology. Methods Systematic review of observational studies evaluating the association between poor hygiene exposures or infections and asthma/wheeze among Latin-American children aged 4-16 years. MEDLINE, EMBASE, LILACS and CINAHL electronic databases were searched following a predefined strategy to 18 December 2017. We quantified outcomes measured and reported, assessed risk of bias and tabulated the results. Results Forty-five studies included: 6 cohort, 30 cross-sectional and 9 case-control studies. 26 cross-sectional studies were school-based surveys (14 of over 3000 children), whereas 5 case-control studies were hospital/health centre-based. Exposures measured and reported varied substantially between studies, and current wheeze was the most common outcome reported. Data showed selective reporting based on statistical significance (P value <0.05): 17/45 studies did not clearly describe the number of exposures measured and 15/45 studies reported on less than 50% of the exposures measured. Most exposures studied did not show an association with wheeze or asthma, except for a generally increased risk associated with acute respiratory infections in early life. Contradictory associations were observed frequently between different studies. Conclusion Selective reporting is common in observational studies exploring the association between environmental exposures and risk of wheeze/asthma. This, together with the use of different study outcomes (wheeze/asthma) associated with possibly distinct causal mechanisms, complicates inferences about the role of poor hygiene exposures and childhood infections in explaining asthma prevalence in Latin-American children.
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Affiliation(s)
| | - Paul Garner
- Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Philip J Cooper
- Facultad de Ciencias Medicas, de la Salud y la Vida, Universidad Internacional del Ecuador, Quito, Ecuador.,Institute of Infection and Immunity, St George's, University of London, London, UK
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Parsons MA, Beach J, Senthilselvan A. Association of living in a farming environment with asthma incidence in Canadian children. J Asthma 2016; 54:239-249. [PMID: 27383380 DOI: 10.1080/02770903.2016.1206564] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
OBJECTIVE The objective of this population-based 14-year follow-up study was to examine the effect of living in a farm environment on asthma incidence in children. METHODS A total of 10,941 children of ages 0 to 11 years who were free of asthma and wheeze at the baseline (1994-1995) in the National Longitudinal Survey of Children and Youth were considered in the study. Children's living environment was classified, based on interviewer's observation, into three categories: non-rural, rural non-farming, and farming. An incidence of asthma was obtained from health-professional diagnosed asthma reported either by the person most knowledgeable for children under 15 years or by the children themselves if they were of ages 16 years and over. RESULTS The 14-year cumulative incidence of asthma among children living in farming environments was 10.18%, which was significantly lower than that observed for children living in rural non-farming (13.12%) and non-rural environments (16.50%). After adjusting for age group, number of older siblings, allergy, parental history of asthma, dwelling in need of repairs and SES index, a dose-response relationship was observed with children living in rural non-farming and farming environments having significantly reduced risk of asthma [hazard ratio (HR): 0.77; 95% confidence interval (CI): (0.60, 1.00); p = 0.047 and HR: 0.56; 95% CI: (0.41,0.77); p < 0.001] in comparison to those living in non-rural environments. CONCLUSION This cohort study provides further evidence that living in a farming environment during childhood is protective of asthma incidence in adolescence and adulthood and this finding provides further support for the hygiene hypothesis.
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Affiliation(s)
- Marc A Parsons
- a School of Public Health, University of Alberta , Edmonton , Alberta , Canada
| | - Jeremy Beach
- b Division of Preventive Medicine, Department of Medicine, University of Alberta , Edmonton , Alberta , Canada
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Apfelbacher C, Frew E, Xiang A, Apfel A, Smith H. Assessment of pet exposure by self-report in epidemiological studies of allergy and asthma: a systematic review. J Asthma 2016; 53:363-73. [PMID: 26539692 DOI: 10.3109/02770903.2015.1099161] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE In epidemiological studies that aim to investigate the relationship between pet exposure and allergy/asthma, pet exposure is often ascertained by means of a questionnaire, but it is unclear which questionnaire items are used. The objective of this study was to systematically review self-reported pet exposure assessment in questionnaires used in epidemiological studies which explore the associations between pets and allergy/asthma. METHODS A systematic literature search was conducted in PubMed and papers were selected according to pre-specified eligibility criteria. The pet exposure questions used were classified within a framework including direct pet contact, indirect pet contact (e.g. through carers or grandparents) and avoidance behaviour. Authors were contacted when the questions used were not reported in detail. RESULTS Ninety-six full text papers were systematically reviewed. All studies assessed direct pet contact, but less than half (45%) explicitly assessed whether pets were allowed indoors. The vast majority of studies assessed both pet exposures during the first year of life and after the first year of life. The minority (13%) assessed whether pet(s) were kept at places regularly visited by the child and pet exposure in utero (15%). Even fewer studies assessed indirect contact to pets (n = 8) and avoidance behaviour (n = 10). CONCLUSIONS In epidemiological studies, the ascertainment of pet exposure through questionnaires appears to vary greatly. This variation might partly explain the inconsistent and contradictory results of the effects of pet exposure on the development of allergy and asthma.
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Affiliation(s)
- Christian Apfelbacher
- a Division of Public Health and Primary Care , Brighton and Sussex Medical School , Brighton , UK and.,b Department of Medical Sociology , Institute of Epidemiology and Preventive Medicine, University of Regensburg , Regensburg , Germany
| | - Edward Frew
- a Division of Public Health and Primary Care , Brighton and Sussex Medical School , Brighton , UK and
| | - Ally Xiang
- a Division of Public Health and Primary Care , Brighton and Sussex Medical School , Brighton , UK and
| | - Alex Apfel
- a Division of Public Health and Primary Care , Brighton and Sussex Medical School , Brighton , UK and
| | - Helen Smith
- a Division of Public Health and Primary Care , Brighton and Sussex Medical School , Brighton , UK and
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Solis Soto MT, Patiño A, Nowak D, Radon K. Prevalence of asthma, rhinitis and eczema symptoms in rural and urban school-aged children from Oropeza Province - Bolivia: a cross-sectional study. BMC Pulm Med 2014; 14:40. [PMID: 24612913 PMCID: PMC3975636 DOI: 10.1186/1471-2466-14-40] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2013] [Accepted: 03/05/2014] [Indexed: 11/16/2022] Open
Abstract
Background Asthma and allergies are world-wide common chronic diseases among children and young people. Little information is available about the prevalence of these diseases in rural areas of Latin America. This study assesses the prevalence of symptoms of asthma and allergies among children in urban and rural areas at Oropeza Province in Bolivia. Methods The Spanish version of the ISAAC standardized questionnaire and the ISAAC video questionnaire were implemented to 2584 children attending the fifth elementary grade in 36 schools in Oropeza province (response 91%). Lifetime, 12 months and severity prevalence were determined for asthma, rhinitis and eczema symptoms. Odds ratios (OR) with 95% confidence intervals (95% CI) were calculated adjusting for age using generalized linear mixed-effects models. Results Median age of children was 11 years, 74.8% attended public schools, and 52.1% were female. While children attending urban schools had lower prevalence of self-reported wheeze in the written questionnaire (adjusted OR 0.6; 95% CI 0.4-1.9), they were more likely than children attending rural schools to report wheeze in the video questionnaire (aOR 2.1; 95% CI 1.0-2.6). They also reported more frequently severe rhinoconjunctivitis (aOR 2.8; 95% CI 1.2-6.6) and severe eczema symptoms (aOR 3.3; 95% CI 1.0-11.0). Conclusion Overall in accordance with the hygiene hypothesis, children living in urban areas of Bolivia seem to have a higher prevalence of symptoms of asthma and allergies compared to children living in the country side. In order to develop primary prevention strategies, environmental factors need to be identified in future studies.
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Affiliation(s)
- María Teresa Solis Soto
- Center for International Health, Ludwig-Maximilians-University, Ziemssenstr, 1, 80336 Munich, Germany.
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Asthma and Microbes: A New Paradigm. THE ROLE OF MICROBES IN COMMON NON-INFECTIOUS DISEASES 2014. [PMCID: PMC7120979 DOI: 10.1007/978-1-4939-1670-2_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Asthma is worldwide at pandemic levels for the past 30 years but is increasing at a greater rate in more affluent societies. It is a heterogeneous disorder caused by interaction between genetic predisposition, atopy, and environmental factors, including allergens, air pollution, and respiratory infections. The pathological aspects and pathophysiological mechanisms are reviewed in this chapter. Allergens or infectious agents may stimulate Th-2 inflammation which causes activation of IL-13, eosinophils, and increase IgE levels, subsequently leading to bronchial smooth muscle hypercontraction. Respiratory viral infections are well-known causes of precipitation of acute asthma exacerbations in 50–60 % of attacks. There is also increasing evidence that bacterial infections, Chlamydia pneumoniae, and Mycoplasma pneumoniae, may contribute to the onset and course of asthma. The two main hypothesis of microbial genesis of asthma that has arisen in the past 20–30 years appears to be incongruous, but are not, are the hygiene hypothesis of asthma, and the virus-related asthma, early onset of viral bronchiolitis in the susceptible hosts being responsible for later development of asthma. The clinical and experimental evidences to support these contentions are reviewed and critiqued.
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Abstract
PURPOSE OF REVIEW It has been hypothesized that increased cleanliness, reduced family size, and subsequent decreased microbial exposure could explain the increases in global asthma prevalence. This review considers the recent evidence for and against the 'hygiene hypothesis'. RECENT FINDINGS Recent evidence does not provide unequivocal support for the hygiene hypothesis: the hygiene hypothesis specifically relates to atopic asthma, but some of the protective effects (e.g. farm exposures) appear to apply to both atopic and nonatopic asthma; asthma prevalence has begun to decline in some western countries, but there is little evidence that they have become less clean; Latin American countries with high infection rates have high asthma prevalence and the hygiene hypothesis relates to early-life exposures, but exposures throughout life may be important. SUMMARY There is a considerable body of evidence which warrants scepticism about the hygiene hypothesis. However, these anomalies contradict the 'narrow' version of it in which microbial pressure early in life protects against atopic asthma by suppressing T-helper 2 immune responses. It is possible that a more general version of the hygiene hypothesis is still valid, but the aetiologic mechanisms involved are currently unclear.
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The farm effect, or: when, what and how a farming environment protects from asthma and allergic disease. Curr Opin Allergy Clin Immunol 2013; 12:461-6. [PMID: 22892709 DOI: 10.1097/aci.0b013e328357a3bc] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
PURPOSE OF REVIEW Multiple studies have shown that the prevalence of asthma and atopy is reduced in children raised on traditional dairy farms. This article discusses the temporal constraints for the protective farm effect, the components of a farming environment that are associated with protection, and novel mechanisms that may underlie protection from asthma and atopy in farming populations. RECENT FINDINGS Protection from asthma and allergy is strongest when exposure occurs in utero or early in life, but the protective effects can persist into adulthood. Just three exposures (contact with cows and straw and consumption of unprocessed cow's milk) account for virtually all the protective farm effect for asthma but not atopy. Whey proteins appear to be critical for the protective effects of farm milk, whereas the high microbial diversity existing in a farm environment is strongly and inversely associated with asthma, but only weakly associated with atopy. Therefore, distinct mechanisms are likely to mediate protection from asthma and atopy. The biological significance of microbial diversity is still unclear, but multiple lines of evidence link the asthma-protective and allergy-protective effects of farming to immune responses and the microbiome. Work in mouse models is revealing novel cellular and molecular mechanisms through which the microbiota may modulate immune responses and allergic inflammation, and thus contribute to the farm effect. The role of the host's genetic makeup, on the contrary, remains poorly understood. SUMMARY The discovery of the central role played by microbial diversity in the asthma-protective and allergy-protective effects of farming warrants metagenomic studies that concertedly and longitudinally investigate the microbiome, the genome, and the immune system of farmers and the farms they live on.
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Abstract
PURPOSE OF REVIEW Several population-based studies have replicated the finding that exposure to a farm environment is protective against the development of atopic diseases. From these studies, novel insights into potential allergy-protective mechanisms were retrieved. This review focuses on consistent and novel findings of immune mechanisms involved in the 'farm effect'. RECENT FINDINGS The most recent studies suggest that the 'farm effect' mediated by microbial exposure may be attributed to both microbial diversity and species specificity. There is convincing evidence that farm milk components and grass arabinogalactan, commonly found in cowshed, may be important. Furthermore, early exposure to a farming environment, in particular in utero, showed stronger effects than exposure later in life, potentially through modulation of the immature immune system by microbes, also involving epigenetic changes. This protective 'farm effect' remains in later adulthood. Regarding gene-environment interactions, polymorphisms in GRM1 interacted with farming in a genome-wide interaction scan for asthma. SUMMARY The novel studies strengthen the role of microbial exposure and farm milk and grass components, especially early in life, in the modulation of the immune system towards a Th1/Treg predominance. This may subsequently lead to a long-lasting lower risk of developing atopic diseases.
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