Asthma in African Americans: What can we do about the higher rates of disease?
ABSTRACTAfrican Americans not only have a higher prevalence of asthma than whites, they also are encumbered with higher rates of asthma-associated morbidity and death. Factors such as genetics, socioeconomic status, health maintenance behaviors, air quality, and obesity likely contribute in combination to these burdens. Further work is needed to better understand these complex risk factors. To remedy these disparities, we need to ensure that patients at higher risk are given proper care and the knowledge to control their asthma.
KEY POINTS
- To better identify those at risk, researchers are looking at genetic markers such as polymorphisms in ADRB2 and CD14.
- Exposure to tobacco smoke and to cockroach allergen contribute to higher rates of asthma prevalence and morbidity.
- African Americans are more likely to receive suboptimal care, in particular to be misdiagnosed with other conditions, to not receive inhaled corticosteroids, and to not receive proper follow-up.
- Better physician-patient communication is one of the keys to improving this problem.
MEDICATION ADHERENCE RATES ARE DISTURBINGLY LOW
Rates of medication adherence for chronic diseases is disturbingly low, and may be even worse for pulmonary diseases.51 Reported rates of adherence to asthma medications among all patients range from 50% to 60%.52,53 Several studies showed that African Americans have a lower rate of adherence than do whites,53–55 even after adjusting for multiple socioeconomic variables.56
Many explanations have been proposed for this discrepancy, and all likely play a role in particular environments. For example, the incidence of crime in the surrounding area was inversely related to medication adherence after adjusting for socioeconomic factors.57 African Americans may have more concern about side effects associated with inhaled corticosteroid use and may be less likely to understand how these drugs work.52,53 A poor provider-patient relationship has also been cited as a barrier to adherence.55,57 Finally, physicians are more likely to underestimate asthma severity in an African American patient than in a white patient.58
Taking the time to ensure that patients truly understand all aspects of their disease and establishing a health care environment that is culturally appropriate may have a significant impact in patients with asthma.
ENVIRONMENTAL EXPOSURES
Air quality contributes to the greater asthma morbidity observed in urban residents, including African Americans. While poor outdoor air quality has not been clearly linked to a higher incidence of asthma, it has been associated with greater asthma morbidity. Poor air quality may affect individuals of all races, but with respect to ambient pollutants such as particulate matter and diesel exhaust, outdoor air quality is worse in urban environments where greater proportions of people of low socioeconomic status reside.59,60
The most extensively studied components of air pollution are ozone, sulfur dioxide, and particulate matter. These pollutants have been associated with a higher rate of emergency department visits,61,62 worse asthma symptoms,63,64 and higher exhaled nitric oxide levels.65
Tobacco smoke
Despite the substantial success of smoking cessation efforts nationwide, exposure to tobacco smoke continues to be common and is a significant risk factor for poor asthma control. Recent data suggest that African Americans and whites have a similar prevalence of smoking,66 but a study found a very high prevalence in low-income African Americans.67
Active smoking has been associated with worse asthma control and a higher risk of death.68 People with asthma who smoke are less likely to improve in their lung function and symptom scores when treated with short courses of oral glucocorticoids compared with both nonsmokers and former smokers.69
Secondhand smoke hurts too. Many children living in low-income urban areas are exposed to secondhand smoke or environmental tobacco smoke.70,71 Passive exposure in children has been associated with worse asthma outcomes, and data suggest such exposure may be a cause of asthma.68,72–74
Environmental tobacco smoke has also been implicated in gene-environment interactions. Patients who are either homozygous or heterozygous for the Arg allele at codon 16 of the ADRB2 gene (discussed above) had significantly lower FEV1 and forced vital capacity (FVC) values when exposed to passive tobacco smoke. This difference was not seen in people who were not exposed.75
Cockroach allergen
The type and condition of a person’s housing also plays a role in asthma-related morbidity and death. Across several socioeconomic levels, it has been suggested that African Americans have poorer-quality housing compared with whites.76 Some of the conditions found in low-quality houses, such as interruptions in heat, plumbing leaks, and the presence of rodents, have been associated with a higher prevalence of asthma in the household.77
Cockroach allergen exposure and sensitization is a major contributor to asthma morbidity in African Americans, particularly those living in poorer urban areas where cockroach allergen may be the most common indoor allergen.8 Living in older housing in urban areas is associated with higher exposure to cockroach allergen, and with subsequent sensitization.78,79 Exposure to high levels of the major cockroach allergen, Bla g 1, in sensitized individuals has been linked to a greater risk of hospitalization and unscheduled medical visits for asthma. This was not found to be the case for other common indoor allergens, such as dust mite and cat dander.8
However, it is not only exposure to high cockroach allergen levels that puts African Americans at risk. African Americans living in low-income urban areas may also be more likely than whites living in low-income urban areas to become sensitized to cockroach allergen.7,80 This suggests a gene-environment interaction that may be unique to African Americans. Moreover, cockroach sensitization may occur early in life.81,82
While successful cockroach avoidance measures and environmental control may be challenging, such measures have been shown to decrease rates of asthma morbidity.83
OBESITY
Obesity has been linked to an ever-growing list of diseases, one of which is asthma. Obesity is not a unique challenge for African Americans, but recent data from the US Centers for Disease Control and Prevention show that African Americans have a 51% higher prevalence of obesity compared with whites.84
Obesity is a risk factor for greater asthma morbidity and is a significant challenge in the African American community. The rise in obesity rates has paralleled the rise in asthma in recent decades. The higher one’s body mass index, the higher one’s risk of asthma.85 This association appears to be stronger in people without concurrent atopic disease.86 Obesity has also been associated with a poorer response to inhaled corticosteroids and a higher risk of asthma exacerbations.87 Interestingly, significant weight loss has been associated with improvements in both asthma control and lung function.88,89
