Asthma: Overview and Risk Factors

Asthma is a chronic respiratory disease in which bronchial obstruction and bronchospasm lead to dyspnea, wheezing, chest tightness, and/or cough. Key to its pathogenesis is inflammation of the airways. Inflammatory cells, including mast cells, eosinophils, T lymphocytes, plasma cells, and basophils, release histamine, various kinins, leukotrienes, prostaglandins, lipid mediators, tumor necrosis factor a (TNF-a), neuropeptides, substance P, and a host of other inflammatory mediators. Other features are smooth muscle hypertrophy, edema, basement membrane thickening, and mucous accumulation in airways.

The inflammatory process is triggered by allergens, which play a central role in approximately 60% of asthma patients. Other triggers include respiratory infections; inhaled irritants (particularly occupational exposures); stress; exercise; cold temperatures; medications such as aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and beta-blockers. Asthma is also caused by agents to which a person has specific sensitivity, such as aspirin and tartrazine, which is a petroleum-derived colorant.¹

The prevalence of asthma in the United States is approximately 5%. Although the disease commonly begins in childhood, up to 40% of patients develop asthma as adults. Among adult patients, 10% to 20% have occupational asthma. An increase in the global prevalence of asthma over the past 30 years has been attributed to climate change, allergen exposure, urbanization, and air pollution, among other factors, but the precise pathogenesis of the observed increase is not clear. Asthma is more prevalent in affluent countries, leading to the question of whether overuse of antibiotics has led to reduced bacterial antigen exposure and a shift of the immune system to a more atopic phenotype. While air pollution is known to exacerbate asthma, it is not clear whether it can cause the disease.^2,3

Risk Factors

In children, asthma occurs more commonly in boys. Among adults, however, the disease is most prevalent in women over 40. Both mortality and morbidity are greater in African Americans, compared with whites. These differences are attributed in part to socioeconomic factors.⁴

Other risk factors include:

• Atopy.
• Family history. About 75% of children with 2 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 cohort, the Nurses' Health Study II, revealed a linear relation between body mass index (BMI) and risk of asthma, with a relative risk of 2.7 for the most obese group.⁵ Another study showed improvement in objective measures of asthma severity and control for those who lost weight.⁶