Second hand smoke exposure and prevalence of asthma in the US population

Background:

Approximately 25 million people (8.2% of the US population) have asthma, and this rate is climbing. We compared individuals who self-reported never smoking by asthma status to better understand a possible association of second-hand smoke (SHS) exposure with this respiratory illness.

Methods:

Data were obtained from the 1999-2012 NHANES, a nationally representative sample of the US population. Inclusion criteria were participants 20+ years who reported never smoking. We compared participants with self-reported asthma by sociodemographic characteristics, self-reported SHS exposure, and measured cotinine, NNAL, cadmium, and FEV1/FVC ratio. Chi- squared test (categorical variables) and regression models (continuous variables) were performed. Sampling weights were used to account for the complex survey design.

Results:

The prevalence of asthma in never-smokers is 12.1% (n=19,115). Females (63.0%) had significantly more asthma than males (p=0.0005). The burden of asthma was highest in non-Hispanic Whites and non-Hispanic Blacks (p<0.001). More married individuals were asthma-free (63.9%) compared with never married and divorced (p<0.0001). Asthma-free participants were significantly older than those with asthma (45.6 and 43.1 years; p<0.0001). Self-reported SHS exposure was not significantly different between asthma groups (p=0.6073). Cotinine and NNAL were not different between groups (p=0.3639 and p=0.7382) but compared to those with asthma those without had higher cadmium levels (0.336 vs. 0.310; p<0.0001) and higher FEV1/FVC ratio (80.0 vs. 77.8; p<0.0001).

Conclusion:

For the never smoking population, variations are seen in participants with and without asthma by sociodemographics and smoking-related biomarkers but not by self-reported SHS exposure. Understanding these disparities can help to inform healthcare prevention policies.