Doctors had believed that the increased risk of heart disease and lung cancer returned to zero after about 10 years, but the new research casts doubt on this. It found the effects on arteries may be cumulative and that even passive smoking may cause permanent damage.
American researchers who studied almost 11,000 middle-aged adults found that atherosclerosis - thickening of the arteries - was 50 per cent worse in smokers than in non-smokers, as expected. However, it was also 25 per cent worse in past smokers than in people who had never smoked, suggesting a persistent effect of smoking.
The arteries were thickest in those who had smoked most for longest and their thickness was less strongly linked with whether they were current or past smokers. The scientists used ultrasound to measure by how much the walls of the carotid artery thickened over a three-year period.
The study - conducted by researchers at Wake Forest University, North Carolina, and published in the Journal of the American Medical Association - also found a "surprisingly large" correlation between passive smoking and atherosclerosis. In those exposed to other people's smoke for at least one hour a week thickening of the arteries was 20 per cent worse than in those who breathed clean air.
The British Heart Foundation said smokers should not use the findings as an excuse not to give up. A spokesman said: "There are physical changes that occur when you give up that makes stopping smoking a very important issue for preventing heart disease and arteriosclerosis. Nobody has ever said arteries heal themselves up when you stop smoking. What this research says is that they carry on thickening, but the process does slow down."
- Jeremy Laurance
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