Secondhand Smoke Hurts the Heart
Even Low Exposures Make Big Impact
Feb. 12, 2007 -- There is new evidence directly linking exposure to
secondhand smoke with an increased risk for heart disease.
Even low-level indirect exposure to cigarette smoke was associated with a
significant rise in heart disease risk in the research conducted by researchers
from the U.K.'s University of Nottingham.
The study is the first to directly measure secondhand smoke exposure through
levels of a nicotine byproduct in the blood. Previous studies have relied on
participants' recall of exposure.
Compared with people in the study with no detectable exposures to nicotine,
those with low- and high exposure levels also had significantly higher levels
of two important markers of heart disease risk.
"These findings suggest that secondhand smoke exposure has a clinically
important effect on susceptibility to heart disease, even at relatively low
levels of exposure, and they highlight the importance of minimizing the
public's exposure to secondhand smoke," researcher Andrea Venn, PhD, tells
A Known Risk Factor
Smoking is a well-established risk factor for cardiovascular disease. Past
research shows that the risk associated with secondhand smoke exposure is about
a third of that seen in active smokers.
In an effort to further clarify this risk, Venn and colleague John Britton,
MD, examined established blood biomarkers of cigarette smoke exposure and heart
disease risk in 7,599 adults who had never smoked. The participants were
enrolled in the Third National Health and Nutrition Examination Survey (NHANES
III), conducted in the United States.
Sixty-eight percent of those evaluated were women, and the median age of the
study participants was 38.
Blood sample analysis included measurements of cotinine, the nicotine
byproduct used to measure nicotine exposure.
The researchers also examined whether nicotine exposure was associated with
markers of increased heart disease risk. They did this by measuring blood
levels of four markers of disease -- C-reactive protein, white blood cell
count, fibrinogen, and homocysteine.
Slightly less than one out of five study participants had no detectable
cotinine in their blood samples, while the rest had low or high levels.
Eighteen percent of those with low blood levels of cotinine and 56% of those
with high cotinine levels reported living with a smoker or being exposed to
tobacco smoke at work.
Having low and high levels of cotinine was associated with a significant
increase in two of the four heart disease markers, fibrinogen and homocysteine
(fibrinogen is a blood clotting factor. Homocysteine is an amino acid and high
levels have been linked to risk for heart, stroke, and blood vessel disease).
The association persisted even after the researchers controlled for other
risk factors, including obesity, diet, physical activity level, and
No significant association was seen between secondhand smoke exposure and
C-reactive protein or white blood cell count.
While the nicotine exposure levels seen in the exposed nonsmokers were far
lower than those reported for active smokers, the apparent impact of secondhand
smoke on heart disease risk was a third to half that associated with active
smoking, Venn noted.
"Our study shows that very low levels of exposure to secondhand smoke
may be associated with appreciable increases in cardiovascular risk," she