Age-related differences in asthma outcomes in the United States, 1988-2006

Abstract

Background: Relatively little is known about the effect of age on asthma outcomes in adults, particularly at a national level.

Objective: To investigate age-related differences in asthma outcomes in a nationally representative, longitudinal study.

Methods: We analyzed data from the Third National Health and Nutrition Examination Survey (1988-1994) with linked mortality files through 2006. Adults with physician-diagnosed asthma were identified and were divided into 2 age groups: younger adults (17-54 years of age) and older adults (55 years or older). The outcome measures were both cross-sectional (health care use, comorbidity, and lung function) and longitudinal (all-cause mortality).

Results: There were an estimated 9,566,000 adults with current asthma. Of these, 73% were younger adults and 27% older adults. Compared with younger adults, older adults had more hospitalizations in the past year, more comorbidities, and poorer lung function (eg, lower forced expiratory volume in 1 second) (P < .05 for all). During a median follow-up of 15 years, significant baseline predictors of higher all-cause mortality included older age (≥55 vs <55 years old: adjusted hazard ratio [HR], 6.77; 95% confidence interval [CI], 3.15-14.54), poor health status (fair and poor vs excellent health status: adjusted HR, 10.07; 95% CI, 3.75-27.01), and vitamin D deficiency (vitamin D level <30 vs ≥50 nmol/L: adjusted HR, 2.19; 95% CI, 1.05-4.58), whereas Mexican American ethnicity (adjusted HR, 0.31; 95% CI, 0.14-0.65) was associated with lower mortality. Controlling for age, asthma was not associated with increased all-cause mortality (adjusted HR, 1.28; 95% CI, 0.99-1.65).

Conclusion: Older adults with asthma have a substantial burden of morbidity and increased mortality. The ethnic differences in asthma mortality and the vitamin D-mortality link merit further investigation.