Environmental Causes of Asthma in Children

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Environmental Causes of Asthma in Children
A Debate of Causes vs. Triggers
Emily Cohn, Jahan Mohiuddin
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What is Asthma?

• Chronic disease that inflames and narrows the
  airways
• Symptoms include wheezing, chest tightness,
  shortness of breath, and coughing
• Inflammation makes airways hypersensitive and
  reactive
• When airways react, the muscles constrict,
  narrowing the airway
• Increased mucous production

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Pathophysiology of Asthma

• A chronic condition in which the airways
  periodically constrict, inflame, and secrete
  excessive amounts of mucus.
• 2 types allergic and non-allergic.
• Most common chronic childhood disorder in
  developed countries.

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Allergic Asthma

• Triggered by inhaling allergens such as dust
  mites, pet dander, pollens, mold, etc.
• IgE antibodies produced by B cells activate mast
  cells
• Mast cells initiate inflammatory response with
  release of histamine and other granules.
• One of the effects of histamine is an increase in
  blood vessel permeability, leading to edema
  (swelling).

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Non-Allergic Asthma

• Very similar symptoms as allergic asthma but
  non-allergic asthma is characterized by the
  absence of an immune response.
• Caused by factors such as anxiety, stress,
  exercise, cold air, dry air, hyperventilation,
  smoke viruses or other irritants

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Why Is Asthma Important?

• According to Fisk (2000), asthma, allergic
  rhinitis, and other associated airway allergic
  diseases cost 23 billion in terms of health care
  and indirect costs including lost work and lost
  school days.

• Landrigan et al. (2002) estimated the total
  annual costs from US childrens asthma caused by
  environmental exposures at 2.3 billion.
• Between 1980 and 1994 the prevalence of asthma in
  the US increased 75.

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Asthma PrevalenceUnited States, 1980-2004
Lifetime
Current
12-Month
Attack
Source National Health Interview Survey
National Center for Health Statistics
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Asthma Prevalence by SexUnited States, 1980-2004
Lifetime

• Female
• Male

Current
12-Month
Attack
Source National Health Interview Survey
National Center for Health Statistics
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Child and Adult Asthma PrevalenceUnited States,
1980-2004

• Child
• Adult

Lifetime
Current
12-Month
Attack
Source National Health Interview Survey
National Center for Health Statistics
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Adult and Child Asthma PrevalenceUnited States,
1997-2004
Child Lifetime Adult Lifetime
Child Current Adult Current
Child Attack Adult Attack
Source National Health Interview Survey
National Center for Health Statistics
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12-Month Asthma Prevalence by RaceUnited
States, 1980-1996
Black
White
Source National Health Interview Survey
National Center for Health Statistics
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Asthma Prevalence by Race/EthnicityUnited
States, 1997-2004
Lifetime

• Black NH
• White NH
• Hispanic

Current
Attack
Source National Health Interview Survey
National Center for Health Statistics
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Current Asthma Prevalence by MSA Size United
States, 2001
MSA size
Source National Health Interview Survey
National Center for Health Statistics
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Current Asthma Prevalence by Poverty Status
United States, 2004
Poverty
Source National Health Interview Survey
National Center for Health Statistics
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Why is asthma incidence higher now?

• Hygiene Hypothesis
• Emphasis on hygiene and sanitation has changed
  living conditions and reduced infections
• Different environmental exposure
• Increased risk for atopy and asthma

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Causes and Triggers

• Causes
• Genetic
• At least 25 genes associated with asthma1
• Environmental Factors
• Only indoor agents are involved.
• Environmental tobacco smoke2
• Poor air quality2
• Mold
• Dust mites
• Gene-environment interactions

• Triggers
• Allergens
• Airborne irritants
• Respiratory infections
• Exercise
• Weather
• Strong emotions
• Some medications
• Ex aspirin

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Environmental Agents Causes or Just Triggers?
Can environmental factors cause the development
of asthma?
Or do environmental factors only trigger
asthmatic attacks?
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What the literature has to say

• Jaakkola et al. (2005) found that children living
  in homes with mold odor had a gt100 increased
  risk of developing asthma in the following 6
  years.
• Strachan (1988), Dales et al. (1991), Brunekreef
  (1992), and other studies had supporting
  findings.
• According to Etzel (2003) and Strachan (2000),
  environmental tobacco smoke and indoor dust mites
  strongly increase the likelihood of asthma
  development.

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Gold (2000)
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Indoor Exposure Asthma Development Asthma Exacerbations
House dust mite Increased Increased
Environmental Tobacco Smoke Probably increased Increased
Cockroach Maybe Increased Increased
Cat Maybe Increased Increased
Dog Maybe Increased Probably Increased
Etzel RA (2003)
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• The Institute of Medicine has concluded that
  sensitization
• to house dust mites is an important risk factor
  for asthma development Etzel (2003)
• These data strongly suggest that dust mite
  exposure is a risk factor for the development of
  symptomatic asthma in children Gold (2000)

House Dust Mites
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Environmental Tobacco Smoke

• Prenatal maternal smoking is correlated with
  reduced infant airway size, among many other
  things. Gold (2000)
• The influence of ETS on the development of asthma
  among children less than 6 years old is much
  greater than that among school-age children.
  Gold (2000)

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Non-Environmental Causes

• Viral or sinus infections and antibiotic use
• - early antibiotic use that prevents
  differentiation toward TH1 (Delfino 2002)
• -RSV infection in infants is asthma risk factor
  (Sigurs 2000)
• Diet
• Obesity
• Genetics

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Diet and Asthma

• Westernization of societies caused change in
  diet
• Between 1961-1985, the British diet decreased
• Fresh fruit consumption by 26
• Green vegetables by 51
• reduced antioxidants causes increased
  susceptibility to oxidant attack and airway
  inflammation
• Seaton 1993

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Obesity and Asthma

• Reduced residual capacity, increased airway
  responsiveness
• In children, might affect lung growth leading to
  reduced pulmonary function
• Increased airway contractility through chronic,
  low-grade inflammation
• Alteration of serum concentrations of hormones
  which could affect airway function
• Shore 2005

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Genetic Factors of Asthma

• No simple Mendelian pattern of inheritance
• Exhibits polygenic inheritance and genetic
  heterogeneity
• six loci have been implicated
• -chromosomes 6p21,5q, 11q13, 13q, and 12q
• Sandford 2000

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Evidence of Genetic Basis in Causation of Asthma

• in families with asthma in successive
  generations, genetic factors alone explained as
  much as 87 of the development of asthma in
  offspring (Holloway, 1999)
• Harris et al. twin study
• -RR for identical twins was 17.9
• -RR for fraternal twins was 2.3

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Factors which suggest genetic components in
causation of asthma

• Prevalence of asthma in the US differs between
• - males and females
• -racial groups

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Outdoor air pollution and asthma

• Lang and Polansky study in Philadelphia between
  1969-1991
• - concentrations of all major air pollutants
  declined
• -asthma morality rates increased
• American six cities study found no association
  between exposure to PM, NO2, SO2 and prevalence
  of asthma
• Leipzig and Munich study
• Seaton 1993

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Non-environmental Triggers

• Gastroesophageal reflux (AAAAI)
• Exercise
• Smoking
• Stress

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Discussion Questions

• What do you think is the primary cause of asthma?
  
• If there is an environmental component to asthma,
  what kinds of public health implications are
  there?
• What types of public health measures need to be
  created/ enforced to reduce the burden of asthma
  and other chronic diseases?
• Why does correlation not equal causation?
• Why do people so often make the mistake of
  equating the two?
• How does this fact make it difficult to prove
  that environmental factors can cause the
  development of asthma?
• What are your thoughts on the hygiene hypothesis?

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References

• Ober C,Hoffjan S (2006). "Asthma genetics 2006
  the long and winding road to gene discovery".
  Genes Immun 7 (2) 95100.
• Gold DR,Wright R (2005). "Population disparities
  in asthma". Annu Rev Public Health 26 89113.
• Fisk, WJ. 2000. Estimates of potential nationwide
  productivity and health benefits from better
  indoor environments an update. In Indoor Air
  Quality Handbook (Spengler J, Samet JM, McCarthy
  JF, eds). New YorkMcGraw Hill, 4.14.36.
• Landrigan, PJ Schecter, CB Lipton, JM Fahs,
  MC Schwartz, J. Environmental pollutants and
  disease in American children estimates of
  morbidity, mortality, and costs for lead
  poisoning, asthma, cancer and developmental
  disabilities. Environ Health Perspect.
  2002110721728.
• Jaakkola, JJK Hwang, BF Jaakkola, N. Home
  dampness and molds, parental atopy, and asthma in
  childhood a six-year population-based cohort
  study. Environ Health Perspect. 2005113357361.

• Etzel RA. How environmental exposures influence
  the development and exacerbation of asthma.
  Pediatrics. 2003. 112(1 Pt 2)233-9.
• Strachan DP. Damp housing and childhood asthma
  validation of reporting of symptoms. BMJ 1988
• 297 1223-6
• Dales RE, Burnett R, Zwanenburg H. Adverse
  health effects among adults exposed to home
  dampness
• and molds. Am Rev Respir Dis 1991 143 505-9
• Brunekreef B. Associations between questionnaire
  reports of home dampness and childhood
• respiratory symptoms. Set Total Environ 1992
  127 79-89
• Strachan DP. The role of environmental factors
  in asthma. Br Med Bull. 2000. 56(4)865-82.
• Gold DR. Environmental tobacco smoke, indoor
  allergens, and childhood asthma. Environ Health
  Perspect. 2000 Aug108 Suppl 4643-51.
• Brim SSN. Asthma prevalence among US children in
  underrepresented minority populations American
  Indian/Alaska native, chinese, filipino, and
  asian indian. Pediatrics (Evanston).
  2008122(1)e217-22.

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References cont

• Delfino RJ. Epidemiologic evidence for asthma and
  exposure to air toxics Linkages between
  occupational, indoor, and community air pollution
  research. Environmental health perspectives.Supple
  ments. 2002110(suppl 4)573.
• HARRIS JR. No evidence for effects of family
  environment on asthma A retrospective study of
  norwegian twins. American journal of respiratory
  and critical care medicine. 1997156(1)43.
• HOLLOWAY JW. The genetic basis of atopic asthma.
  Clinical and experimental allergy.
  199929(8)1023.
• SANDFORD AJ. The genetics of asthma. the
  important questions. American journal of
  respiratory and critical care medicine.
  2000161(3)202.
• Seaton A. Increase in asthma A more toxic
  environment or a more susceptible population?
  Thorax. 199449(2)171.
• Shore SA, Fredberg JJ. Obesity, smooth muscle,
  and airway hyperresponsiveness. Journal of
  Allergy and Clinical Immunology,. 2005
  5115(5)925-7.
• SIGURS N. Respiratory syncytial virus
  bronchiolitis in infancy is an important risk
  factor for asthma and allergy at age 7. American
  journal of respiratory and critical care
  medicine. 2000161(5)1501.