Asthma is usually diagnosed in childhood. The risk factors for asthma include:
- a personal or family history of asthma or atopy;
- triggers (see Asthma Pathophysiology);
- premature birth or low birth weight;
- viral respiratory infection in early childhood;
- maternal smoking;
- being male, for asthma in prepubertal children; and
- being female, for persistence of asthma into adulthood.
There is a reduced occurrence of asthma in people who were breast-fed as babies. Current research suggests that the prevalence of childhood asthma has been increasing. According to the Centers for Disease Control and Prevention 's National Health Interview Surveys, some 9% of US children below 18 years of age had asthma in 2001, compared with just 3.6% in 1980. The World Health Organization (WHO) reports that some 8% of the Swiss population suffers from asthma today, compared with just 2% some 25–30 years ago. Although asthma is more common in affluent countries, it is by no means a problem restricted to the affluent; the WHO estimate that there are between 15 and 20 million asthmatics in India. In the U.S., urban residents, Hispanics, and African Americans are affected more than the population as a whole. Globally, asthma is responsible for around 180,000 deaths annually.
On the island Tristan da Cunha , 50% of the population are asthmatics due to heredity transmission of a mutation in the gen CC16.
The incidence of asthma is higher among low-income populations, which in the western world are disproportionately minority, and more likely to live near industrial areas. Additionally, asthma has been strongly associated with the presence of cockroaches in living quarters, which is more likely in such neighbourhoods.
The quality of asthma treatment varies along racial lines, likely because many low-income people cannot afford health insurance and because there is still a correlation between class and race. For example, black Americans are less likely to receive outpatient treatment for asthma despite having a higher prevalence of the disease. They are much more likely to have emergency room visits or hospitalization for asthma, and are three times as likely to die from an asthma attack compared to whites. The prevalence of "severe persistent" asthma is also greater in low-income communities compared with communities with better access to treatment.
Asthma and athletics
Asthma appears to be more prevalent in athletes than in the general population. One survey of participants in the 1996 Summer Olympic Games showed that 15% had been diagnosed with asthma, and that 10% were on asthma medication. These statistics have been questioned on at least two bases. Persons with mild asthma may be more likely to be diagnosed with the condition than others because even subtle symptoms may interfere with their performance and lead to pursuit of a diagnosis. It has also been suggested that some professional athletes who do not suffer from asthma claim to do so in order to obtain special permits to use certain performance-enhancing drugs.
There appears to be a relatively high incidence of asthma in sports such as cycling, mountain biking, and long-distance running , and a relatively lower incidence in weightlifting and diving. It is unclear how much of these disparities are from the effects of training in the sport, and from self-selection of sports that may appear to minimize the triggering of asthma.
In addition, there exists a variant of asthma called exercise-induced asthma that shares many features with allergic asthma. It may occur either independently, or concurrent with the latter. Exercise studies may be helpful in diagnosing and assessing this condition.