Breathing secondhand smoke appears to increase levels of two markers for heart disease, the protein fibrinogen and homocysteine (an amino acid), British researchers report.

The lead researcher is Andrea Venn, an associate professor at the University of Nottingham's Division of Epidemiology and Public Health.

The Study

For the study, Venn and coauthor Dr. John Britton collected data on 7,599 adults in the third National Health and Nutrition Examination Survey. None of these people had ever smoked.

Study participants had their blood levels of cotinine, an indicator of nicotine, measured. They also had their levels of fibrinogen, homocysteine and C-reactive protein measured, all factors linked to heart disease.

The researchers found that only 18% of the participants had no detectable levels of cotinine. The other participants had either low or high levels of the substance. Eighteen percent of those with low levels of cotinine and 56% of those with high levels said they lived with a smoker or were exposed to tobacco smoke at work.

The researchers also found that the low- and high-cotinine groups had significantly higher levels of fibrinogen and homocysteine, compared with those who had no detectable levels of cotinine. The increased fibrinogen and homocysteine levels were equivalent to about 30% to 45% of levels seen in active smokers. Fibrinogen and homocysteine are markers for heart disease.

"Furthermore, our study showed that these effects were not restricted to people exposed to high levels of secondhand smoke but were also evident in our low-exposure group, the majority of whom reported not living with a smoker and not being exposed at work," Venn said.

Low Levels Of Secondhand Smoke Still Dangerous

The findings suggest that secondhand smoke has a significant effect on susceptibility to cardiovascular disease, even at relatively low levels of exposure, Venn said. "Secondhand smoke is likely to be an important avoidable cause of cardiovascular disease in the population, and it is therefore important that measures are implemented to minimize the public's exposure to secondhand smoke," she said.

"Contrary to what the tobacco companies will tell you, there is overwhelming evidence that even secondhand smoke is harmful," said Dr. Byron Lee, an associate professor of cardiology at the University of California, San Francisco.

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