Secondhand smoke exposure and serum cotinine levels among current smokers in the USA.
BACKGROUND
Secondhand smoke (SHS) likely provides additional exposure to nicotine and toxins for smokers, but has been understudied. Our objective was to determine whether SHS exposure among smokers yields detectable differences in cotinine levels compared with unexposed smokers at the population level.


METHODS
Using the US National Health and Nutrition Examination Survey (NHANES) for the years 1999-2012, we compared serum cotinine levels of 4547 current adult cigarette smokers stratified by self-reported SHS exposure sources (home and/or work) and smoking intensity. A weighted multivariable linear regression model determined the association between SHS exposure and cotinine levels among smokers.


RESULTS
Smokers with SHS exposure at home (43.8%) had higher cotinine levels (β=0.483, p≤0.001) compared with those with no SHS exposure at home after controlling for the number of cigarettes smoked per day and number of days smoked in the previous 5 days, survey year, age, gender and education. Smokers with SHS exposure at work (20.0%) did not have significantly higher cotinine levels after adjustment. The adjusted geometric mean cotinine levels of light smokers (1-9 cigarettes per day) with no SHS exposure, exposure at work only, home only, and both home and work were 52.0, 62.7, 67.2, 74.4 ng/mL, respectively, compared with 219.4, 220.9, 255.2, 250.5 ng/mL among moderate/heavy smokers (≥10 cigarettes per day).


CONCLUSIONS
Smokers living in residences where others smoke inside the home had significantly higher cotinine levels than smokers reporting no SHS exposure, regardless of individual smoking intensity. Future research should target the role that SHS exposure may have in nicotine dependence, cessation outcomes and other health impacts among smokers.
Master of Public Health Program, Idaho State University-Meridian Campus, Meridian, Idaho, USA.
Ryan P
RP
Lindsay
Department of Psychiatry, University of California, San Francisco, San Francisco, California, USA.
Janice Y
JY
Tsoh
Institute for Health & Aging, University of California, San Francisco, San Francisco, California, USA.
Hai-Yen
HY
Sung
Institute for Health & Aging, University of California, San Francisco, San Francisco, California, USA.
Wendy
W
Max
D000328:Adult; D015415:Biomarkers / Q000097:blood; D003367:Cotinine / Q000097:blood*; D005260:Female; D006798:Housing; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects; D016014:Linear Models; D008297:Male; D015999:Multivariate Analysis; D009749:Nutrition Surveys; D016273:Occupational Exposure / Q000009:adverse effects; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000097:blood* / Q000208:ethnology; D013997:Time Factors; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*; D014481:United States / Q000453:epidemiology; D017132:Workplace; D055815:Young Adult
D015415:Biomarkers; D014028:Tobacco Smoke Pollution; D003367:Cotinine
Cotinine; Secondhand smoke; Smoking topography; Surveillance and monitoring