Risk Factors

Asthma affects about 5 million American children between the ages of 5 and 14. Asthma has dramatically increased worldwide over the last few decades, in both developed and developing countries. From 1980 to 1994, asthma increased 160% in children younger than 4 years old and has risen dramatically in other countries as well. There is a wide variation in asthma incidence, however, ranging from over 50% among children in the Caroline Islands to virtually 0% in Papua New Guinea. The reasons for this wide variation are not yet known.

Gender

Among younger children, asthma develops twice as frequently in boys as in girls, but after puberty it may be more common in girls.

Socioeconomic Factors

Urban Life. Urban life is strongly associated with a higher risk. Although poverty plays a significant role, urban life, in fact, has been associated with a higher risk for asthma in any income group and among both children and adults. In some urban areas, as many as 25% of children have asthma or show signs of wheezing. In fact, it may be greatly underdiagnosed in city children. A 1999 Chicago study reported almost a third of children in inner-city kindergartens had asthma symptoms without a diagnosis of the disorder; 10% had actually been diagnosed with asthma, mainly because their symptoms were severe.

Ethnicity. Since 1980, asthma rates have risen the most dramatically among African American children, and they have significantly higher rates of asthma than Caucasian children. Hispanic children are also at higher risk. Both groups of minority children are more likely to have fatal asthma than Caucasian children.

Some studies indicate that the difference in risk exists simply because African Americans and other minority groups are more likely to live in urban areas. Poverty and lack of access to health care also play a role. However, Caucasian children who live in cities also face a high risk for asthma, and rural African-American children do not.

Urban life and socioeconomic factors, however, may not fully explain the ethnic disparity. For example, a 2000 study found that African-American children may have significantly higher levels of IgE than Caucasian children, suggesting a genetic susceptibility. (IgE are immune factors that play a critical role in asthma.)

Issues Surrounding Birth

Low Birth Weight. Infants of low birth weight are at higher risk for lung problems and asthma.

Winter Birth. One study suggests that children born in the winter are at greater risk for asthmatic allergies to cockroaches than children born at other times of the year.

Vitamin D. A 2006 study suggested a link between vitamin D intake during pregnancy and development of early childhood asthma. Pregnant women who had a higher intake of vitamin D were less likely to give birth to children who developed asthma.

Breast Feeding. Most studies on breastfeeding report some protection against wheezing and asthma in the first year of life. It should be noted that breastfeeding has many other benefits for the child as well. The American Academy of Pediatrics recommends exclusively breastfeeding for the child's first 6 months of life.

Complications of Pregnancy. According to a 2000 study, complications of pregnancy, specifically those involving the mother's uterus (such as post-birth hemorrhage, pre-term contractions, insufficient placenta, and restricted growth of the uterus), are associated with an increased risk of childhood asthma. Another study also reported that delivery procedures such as Cesarean section, the use of vacuum extraction or forceps also raised the risk of childhood asthma.

Obesity

In both adults and children, the incidence of obesity and asthma has been increasing 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 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. [See In-Depth Report #53: Weight control and diet.].

Other Risk Factors

Damp Homes. Studies from different parts of the world reported that children who live in damp homes have a much higher risk for asthma.

Parental Migraines and Childhood Asthma. Some studies have reported a link between childhood asthma and parental migraines, with one small study suggesting that children are about five times more likely to develop asthma if their parents have a history of migraines.

Mental Health. Research indicates that poor mental health of parents and children are significant predictors of more severe symptoms in childhood asthma. A 2000 study suggested that high stress levels can predict the onset and severity of asthma in children genetically at risk for asthma.