Childhood Asthma and the Environment

Childhood Asthma Facts

Childhood Asthma and Allergens

Childhood Asthma and Tobacco Smoke

Childhood Asthma and Air Pollution

Links and References

Childhood Asthma Facts

Definition of Asthma
Symptoms of Asthma
Diagnosis of Childhood Asthma
Increasing Asthma Prevalence in Children
Impact of Childhood Asthma
Risk Factors for Asthma
Protective Factors for Asthma

Definition of Asthma

  • Asthma is a chronic disorder of the lungs that involves airway inflammation, increased mucous production and over-reactive smooth muscles in which obstruction of airflow within the small airways is partially or fully reversible.
  • Asthma exacerbations result from an intense hyper-responsiveness of the small airways to multiple triggers that include infection, irritants, allergens, changes in weather conditions, emotions and exercise.
  • It is important to make the distinction between asthma, the chronic condition and asthma exacerbations. Although the symptoms of asthma can wax and wane and may even improve with age and treatment, there is concern that the airway inflammation underlying asthma may never really go away.

Symptoms of Asthma

  • Up to 80% of children with asthma develop symptoms before age 5 years.
  • Asthma symptoms are often under-recognized and under-treated by both parents and healthcare providers.
  • Common symptoms of childhood asthma may include cough, wheeze, breathlessness or chest tightness, frequently associated with colds, sleep or exercise.

Symptoms of Asthma

Source: Atlas of Allergic Diseases 1

  • Triggers of asthma symptoms include allergens, exercise, cold air, emotional stress, viruses, air pollution, foods and food additives, medications and chemical and irritant exposures.

Triggers of Asthma Symptoms

Source: Atlas of Allergic Diseases 1

Frequently multiple factors are involved in the triggering of an asthma exacerbations. 2

Diagnosis of Childhood Asthma

  • Asthma is diagnosed by identification of the presence of a classic pattern of symptoms of recurrent airway hyper-reactivity including cough, wheeze, shortness of breath and chest tightness after the exclusion of any underlying conditions that could masquerade as asthma. 3
  • The National Asthma Education and Prevention Program Expert Panel Report 2: Guidelines for the Diagnosis and Management of Asthma contains clinical guidelines for quality asthma care. 3


Click here to view these guidelines: http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm

  • The American Thoracic Society’s definition of asthma, the presence of four out of five following clinical parameters has shown to be highly sensitive and specific in making the diagnosis of asthma. These parameters include:
    • Wheezing with colds
    • Wheezing apart from colds
    • Difficulty breathing associated with wheeze
    • Wheezing after exertion
    • Persistent cough
  • Physical exam may be remarkable for prolonged exhalation phase, increased effort of breathing, wheezing or diminished lung sounds and in severe cases cyanosis.
  • Due to the variable nature and fluctuating course of asthma, all clinical exam features may be normal.
  • The diagnosis of asthma may be confirmed in children older that age 4 through pulmonary function tests that demonstrate reversible airflow limitation.
  • Chest x-ray may show hyperinflation of the lungs when airway inflammation and reactivity are severe.

Air Trapping with Hyperinflation in an 8 year old Asthmatic

    Source: Atlas of Allergic Diseases 1

Increasing Prevalence of Asthma in Children

  • Asthma is the most common chronic condition of childhood.
    o Approximately 6.3 million children under age 18 in the United States have asthma.
  • Both the incidence of asthma and asthma-related deaths have increased in children worldwide over the past 20 years.
    • Children aged 0 to 4 years had the largest increase in prevalence and had greater health care use, but adolescents have the highest mortality. 4

Asthma Prevalence by Age and Year

Source: Global Initiative for Asthma

Peak asthma prevalence was 7.5% in 1995. In 1997, asthma attack prevalence was reported at 5.4%, but changes in the NHIS design in 1997 preclude comparison to previous estimates. Asthma attack prevalence remained level from 1997 to 2000. 4

Impact of Childhood Asthma

  • Asthma accounts for over 14 Million missed school days per year in the US.
  • Poorly controlled asthma can result in exercise intolerance, disrupted sleep, decreased energy levels, impaired concentration or slowed growth.
  • Whereas many children may outgrow their asthma symptoms, there is increasing concern that the underlying inflammatory process within the airways may never completely resolve.
  • Racial and ethnic disparities remain large for asthma health care utilization and mortality. The asthma burden is born disproportionately by black children. 4

Asthma Mortality by Race and Sex


Source: Global Initiative for Asthma

Risk Factors for Asthma

An individual’s lifetime risk for developing asthma depends upon a complex interaction of hereditary and environmental factors. Risk factors that have been identified include: 5 6

  • Genetic Predisposition
    • Family history of atopy or asthma in a parent key risk factors in the development of asthma. 7
  • Perinatal Factors
    • Prematurity with respiratory distress increases the risk of episodes of wheezing throughout childhood.
  • Allergen Exposures
    • Risk factors for the development of asthma include sensitization and exposure to cockroaches, house dust mites, and the mold, Alternaria. 7
  • Infections
    • Respiratory infections, especially those caused by respiratory syncytial virus, are a significant risk factor for the development of wheezing in childhood. 7
  • Air Pollution
    • Persistent environmental exposure to particulate air pollution from motor vehicles has been suggested to be an important factor contributing to the observed increased prevalence of asthma and allergies. 8, 9 10
  • Tobacco Smoke
    • Tobacco smoke has been associated with enhancement of respiratory allergy to inhaled allergens in addition to being an irritant. 11 12
  • Diet and Obesity
    • Early introduction of solid food before the three months of age is a significant factor increasing probability for developing asthma. 13
    • Evidence suggests elevated body mass index and dietary patterns, especially intake of dietary lipids, contribute to symptoms of asthma. 14

Protective Factors for Asthma

  • Early life exposures have been shown to reduce the likelihood of the development of asthma or allergies. In addition, avoidance of known risk factors may also reduce or delay the development of asthma in susceptible individuals. 15
  • The “Hygiene Hypothesis” suggests that the development of protective immune responses to microbes early in life may reduce the likelihood of the development of allergies and as a result the development of asthma. 16
    • Positive allergy skin tests for most allergens have been found to be more prevalent among children living in urban areas compared with in rural areas. 17
  • Microbial exposures may also explain the protective nature of the following:
    • Older Siblings
    • Daycare Attendance
    • Probiotics
    • Animal Exposures
  • Breastfeeding and Dietary Factors
    • Observational studies have shown a 30%-50% reduction in childhood asthma with exclusive breastfeeding for three months, and similar reductions in children who eat fish regularly and have a high intake of omega-3 fatty acids. 18 19
    • People who have a diet rich in fruit and vegetables have a lower risk of poor respiratory health, and that this may be due to the antioxidant nutrients these foods contain, particularly vitamin C and, to a lesser extent, vitamin E. 20 21
    • Antioxidant vitamins could also play an important role in gene-environment interactions in complex lung diseases such as childhood asthma. 21

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