Purpose: To assess the overall prevalence of asthma and the association between family history of asthma and the prevalence of asthma among US adults.
Methods: We analyzed National Health and Nutrition Examination Survey data from 1999 to 2004 for 15,008 respondents aged 20 years or older with no history of emphysema. We divided respondents into three familial risk groups (high, moderate, and average) on the basis of the number and closeness of relatives, that they reported as having asthma and then assessed the asthma prevalence in each. We also assessed associations between asthma prevalence and age, sex, race/ethnicity, income, body mass index, smoking status, household smoking exposure, and physical activity.
Results: By our definitions, 2.3% of respondents were at high, 13.0% at moderate, and 84.7% at average familial risk for asthma. The crude prevalence of self-reported lifetime asthma was 11.5% (95% confidence interval [CI]: 10.7-12.3%) among all respondents, and 37.6% (95% CI: 30.4-45.4%), 20.4% (95% CI: 18.2-22.7%), and 9.4% (95% CI: 8.7-10.2%) among those at high, moderate, and average familial risk, respectively. Among all risk factors we looked at, family history had the strongest association with lifetime asthma prevalence, and the association remained significant after adjustments for other risk factors. Compared with average familial risk, the adjusted odds ratios for lifetime asthma were 2.4 (95% CI: 2.0 -2.8) for moderate and 4.8 (95% CI: 3.5-6.7) for high familial risk.
Conclusion: Our findings showed that a family history of asthma is an important risk factor for asthma and that familial risk assessments can help identify people at highest risk for developing asthma. Additional research is needed to assess how health care professionals can use family history information in the early detection and management of asthma.