Asthma risk is up to six times higher for those with a strong family history, says a new study.
"Our findings showed that a family history of asthma is an important risk factor for asthma, and that familial risk assessments for asthma can help identify people at highest risk for developing asthma," said lead author Tiebin Liu, M.S.P.H., and colleagues of The U.S. Centers for Disease Control and Prevention.
For the study, the researchers analyzed 1999 to 2004 data on 1,500 adults (20 or older) from the National Health and Nutrition Examination Survey (NHANES) study.
Based on the number and closeness of relatives with asthma, participants were classified as being at high, moderate, or average risk of asthma.
About two percent of people were at high risk and thirteen percent at moderate risk; the remaining 85 percent were at average risk
Asthma prevalence increased from 9.4 percent for people at average risk, to 20.4 percent for those at moderate risk, to 37.6 percent for those at high risk. Asthma risk was 2.5 times higher in the moderate-risk group and 5.8 times higher in the high-risk group.
After adjustment for other factors, risk was 2.4 times higher in the moderate-risk group and 4.8 times higher in the high-risk group, compared to people at average risk.
Other asthma risk factors included African American race, low income, obesity, smoking or living with a smoker, and physical inactivity.
Asthma occurred at younger ages in people with a family history. Average age at onset decreased from 22 years in the average-risk group, to 19 years in the medium-risk group, to 17 years in the high-risk group.
The new study suggests that asthma risk is at least two times higher in people with a moderate family history (for example, one parent or sibling with asthma), and up to six times higher for those with a strong family history (for example, both parents affected).
The researchers have called for more research into the role of family history in diagnosing asthma, and whether this information can help to reduce the disease's harmful effects.
The study has been reported in the May issue of Genetics in Medicine.