Risk Factors

According to a major national 2001 survey, American adults have a 10% lifetime risk for developing asthma. As of 2002, an estimated 20 million adults had the disorder. Between 1980 - 1996 the prevalence of asthma increased by nearly 74%, but it may be stabilizing. Other respiratory diseases, sinusitis, and ear infections are also on the rise, suggesting that airborne or environmental factors may be at work that affects all of these conditions, including asthma.

Gender

Before puberty, asthma occurs more often in males, but after adolescence, it appears to be more common in females. In adults with similar cases of actual airway obstruction, women are likely to report more severe symptoms than men are. In addition, women may be at much greater risk of death from asthma than men.

Obesity

In both adults and children, the incidence of obesity and asthma has been increasing in parallel over recent years. Studies report a strong association between the two conditions. Some experts suggest that excess weight pressing on the lungs may trigger the hyperreactive response in the airways typical of asthma. Others believe that asthma leads to obesity by inhibiting physical activity, although several studies have found no difference in activity levels between people with or without asthma. Some studies suggest that many obese people may be misdiagnosed as having asthma when in fact they are simply short of breath, possibly because of the increased effort required for breathing.

In any case, there is evidence that losing weight can relieve asthma symptoms. Some evidence also suggests that people who are overweight (body mass index greater than 25) have more difficulty getting their asthma under control. Weight loss in anyone who is obese and has asthma or shortness of breath reduces airway obstruction and improves lung function.

Smoking

In one study of elderly people with severe adult-onset asthma, smoking was the most significant risk factor for developing this condition. Smoking, in any case, contributes to decline in lung function in everyone.

Population Differences

Urban Life and Poverty. African Americans have higher rates of asthma than Caucasians or other ethnic groups. They are also more likely to die of the disease. Ethnicity and genetics, however, are less likely to play a role in these differences than socioeconomic differences, such as having less access to optimal health care. Poverty is a consistent risk factor in most studies. Both the elderly and the urban poor have the highest risk for severe asthma and death. Urban life, in fact, has been associated with a higher risk for asthma in all income groups and among both children and adults. Twin studies also suggest that people who have lower educational levels (as well as those who exercise less) are at higher risk for adult-onset asthma, further suggesting a link to lower economic status.

Geographical Differences. Asthma rates vary widely among different populations regardless of socioeconomic or other factors. For example, asthma and hospitalization rates are dramatically higher in New York Puerto Ricans than in Hispanic Americans who live in Los Angeles or the Southwest. Among the U.S. states, rates are lowest in Louisiana and highest in Maine.

There are significant differences among nations. In a 2001 study of 22 nations, the countries with the highest asthma rates were Britain, Ireland, Australia, New Zealand, and the U.S. (According to another study, asthma rates are also significantly higher in Canadian adults than they are in comparable European groups.) Low rates were reported in Iceland, Norway, Spain, Germany, Italy, Algeria, India, and Eastern European nations. The reasons for these variations are still unknown.

Review Date: 12/21/2006
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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