Exposure to second-hand smoke at work, home or elsewhere results in a disproportionate rise in markers that increase the risk of cardiovascular disease, University of Nottingham researchers have found.
A new study published in Circulation, a journal of the American Heart Association, measured the level of cotinine in participants' blood, rather than relying on participants' self-reporting of exposure to second-hand smoke. Cotinine is the major metabolite of nicotine that indicates levels of nicotine intake.
Since nicotine is highly specific for tobacco smoke, blood serum cotinine levels track exposure to tobacco smoke and its toxic components.
Dr Andrea Venn, lead author of the study and associate professor in the Division of Epidemiology and Public Health at The University of Nottingham, said: “Our study provides further evidence to suggest low level exposure to second-hand smoke has a clinically important effect on susceptibility to cardiovascular disease.
“This is the first epidemiological study to relate the levels of these markers to an objective measure of second-hand smoke exposure, rather than self-reported exposure, which can be biased.”
Dr Venn and co-author Professor John Britton checked to see if people exposed to second-hand smoke had increased levels of fibrinogen, homocysteine and C-reactive protein — all markers of cardiovascular disease. Researchers examined data from the third National Health and Nutrition Examination Survey (NHANES III, 1988–94), which included 7,599 adults who had never smoked.
Sixty-eight percent of the participants were women, with participants' median age being 38. Eighteen percent of participants had no detectable levels of cotinine; the rest were classified as having either low or high cotinine. Eighteen percent of participants with low levels of cotinine and 56 percent of subjects with high levels of cotinine reported living with a smoker at home or being exposed to tobacco smoke at work, the primary places for long-term exposure.
Researchers found the low- and high-cotinine groups had significantly higher levels of fibrinogen and homocysteine than the ‘no detectable' group, with fibrinogen levels estimated at 9–10 milligrams per decilitre higher and homocysteine levels at 0.8 micromoles per litre higher.
Dr Venn said: “The increased levels of fibrinogen and homocysteine seen in relation to second-hand smoke exposure were equivalent to about 30 per cent to 45 per cent of those seen for active smoking.”
The researchers also investigated elevated C-reactive protein, another inflammatory marker, and white blood cell count in participants with elevated cotinine levels. They found no significant association.
The effect levels seen for fibrinogen and homocysteine were about twice as high when measuring cotinine levels compared to previous studies based on self-reported exposure.