Asthma: Overview and Risk Factors

Asthma is a chronic respiratory disease marked by inflammation and obstruction of the airways, leading to shortness of breath, wheezing, chest tightness, and cough. In severe cases, additional symptoms may include difficulty taking deep breaths and difficulty finishing sentences.

Asthma is usually triggered by allergens. Other triggers include respiratory infections, inhaled irritants (particularly occupational exposures and tobacco), stress, exercise, cold temperatures, and medications (e.g., beta–blockers, aspirin, and nonsteroidal anti–inflammatory drugs such as ibuprofen).

About 5 percent of people in the United States have asthma. Although the disease commonly begins in childhood, up to 40 percent of patients first develop asthma as adults. An increase in the global rate of asthma over the past 30 years has been attributed to climate change, allergen exposures, urbanization, and air pollution, among other factors, but the precise reasons for this increase are not clear.

Asthma is more common in developed countries, leading to the question of whether dietary factors, chemical exposures, or overuse of antibiotics may be the cause. While air pollution is known to cause flare–ups of asthma, it is not clear whether it can cause the disease.

Types of Asthma

• Mild intermittent asthma: Symptoms occur only intermittently. This type is treated on an as–needed basis with inhaled medications, such as albuterol, that widen the airways.
• Mild persistent asthma: Symptoms are mild, but occur on a regular basis. This type is treated by daily use of inhaled steroids, along with albuterol when symptoms occur. Inhaled steroids have been shown to decrease the risk of flare–ups and hospitalizations, and reduce the need for albuterol. Common inhaled steroid medications include budesonide, fluticasone, triamcinalone, and beclomethasone.
• Moderate persistent: Symptoms are harsher and occur on a regular basis. This type is treated with an increased daily dose of inhaled steroids, in addition to other medications (e.g., salmeterol, montelukast, theophylline, and cromolyn) as well as albuterol during flare–ups. Failure to control symptoms with the use of two of the above medications suggests the individual may have severe asthma or perhaps another diagnosis.
• Severe asthma: Severe asthma requires high–dose inhaled steroids or oral steroids, along with other controller medicines. This type of disease is serious, and patients may require frequent hospitalization.

Risk Factors

In children, asthma occurs more commonly in boys. Among adults, however, the disease is most common in women over 40. African–Americans tend to have more severe disease, compared with whites.

Other risk factors include:

• Other allergic diseases (e.g., eczema or food allergy)
  
• Family history: About 75 percent of children with two asthmatic parents also have asthma.
  
• Environmental and occupational factors: These factors include tobacco smoke, animal dander, dust mites, plants, pollen, mold, enzymes, chemicals, and metals.
  
• Obesity: A large study, the Nurses’ Health Study II, revealed that women with the highest body mass index had the greatest risk of asthma. The most obese had nearly three times the risk, compared with individuals of normal weight. Another study showed improvement in asthma severity and control for those who lost weight.