'Unknown exposure to second-hand smoke may up mortality risk'

Known and unknown exposure to second-hand smoke may lead to an increased risk of mortality in non-smokers, a new study has warned.
The results provide a more accurate way to gauge second-hand smoke exposure than questionnaires, and present a strong case for more stringent limits on smoking and increased preventive screenings for those more likely to have been exposed to second-hand smoke, researchers said.
Researchers from the Icahn School of Medicine at Mount Sinai in the US used serum cotinine, a metabolite of nicotine, as a biological marker of exposure to second-hand smoke and linked National Health and Nutrition Examination Survey data to overall and cause-specific mortality in 20,175 non-smokers.

After adjustment for sex, education, race/ethnicity, body mass index and smoking habits, their analysis showed a significant increase in years of life lost (YLL) across cotinine concentrations.
In the adjusted analysis, the lowest quartile of cotinine concentration - below the detectable level - was associated with 5.6 YLL while the highest quartile was linked to 7.5 YLL.
"A crucial finding of this study is that non-smokers are exposed to second-hand smoke without even realising it," said Raja Flores, Professor at the Icahn School of Medicine at Mount Sinai.

"Questionnaires show that responders do not know they were exposed to smoke, but cotinine blood levels are more accurate in determining their exposure and subsequent risk of lung cancer and other smoking-related disease," said Flores.

Further analysis among non-smokers who reported no exposure to second-hand smoke and had cotinine levels below race-specific cutoffs found that the association between exposure and mortality remained similar to observations in subjects who reported exposure.
Specifically, increases in serum cotinine were statistically significantly associated with lung cancer, all cancers, and heart disease, researchers said.
"Using cotinine level to measure exposure to second-hand smoke has important public health implications, because increasing the scope of smoke-free environments would likely decrease cotinine levels in the general population and ultimately death," said Emanuela Taioli, Director of the Institute for Translation Epidemiology at Mount Sinai.

The study was published in the journal Carcinogenesis.