Decades of tobacco trigger change in lungs, say researchers. 'Once this switch is turned on, it appears to be permanent, which may explain why long-term ex- smokers who have not had a cigarette in 25 years are still at high risk for getting cancer'
The deadly nature of cigarettes was reemphasized with a new study suggesting that people who have smoked for more than 25 years may have caused lung cell damage which cannot be stopped by quitting.
According to researchers from the University of Pittsburgh, long-term smoking appears to trigger a biological switch in the lungs which causes cell growth and this in turn could lead to cancer.
The researchers looked at three groups: non-smokers, those who had smoked for less than 25 years, those who had smoked for longer.
In people who smoked at least 20 a day for 25 years, the doctors found significantly more evidence of a protein called GRP, which spurs lung cells to divide.
They say that 77 per cent of the long-term smokers showed the protein, but it appeared in only 15 per cent of those who had smoked for less than 25 years. The long-term smokers showed the protein even if they had stopped smoking some time ago.
Dr Jill Siegfried, of Pittsburgh University's lung cancer centre, who led the research, said: "Once this switch is turned on, it appears to be permanent, which may explain in part why long-term ex-smokers who have not had a cigarette in over 25 years are still at high risk for getting lung cancer."
She said, however, there was potential good news in the findings, as the protein could help identify patients at high risk of lung cancer who could receive early treatment. In the longer term, if a way could be found of turning off the "switch" it could mean ex-smokers would not get lung cancer.
The anti-smoking group Action on Smoking and Health said the research should not be seen as an excuse for long-term smokers not quitting.
A spokesman said: "Most smokers die from heart disease. Stopping smoking reduces the risk of heart disease almost immediately. It's always worth giving up, whatever your age, but the sooner the better." Dr Jean King, of the Cancer Research Campaign, said smoking caused at 24 separate diseases and there were clear benefits from stopping at any time.
“There are immediate benefits, short-term benefits and long-term benefits from quitting smoking. This is a small scale study and it doesn't change the message that stopping smoking brings clear benefits both for individuals and their families."
Dr. King added: "Within two years of stopping smoking the increased of heart disease is halved. Even if the findings for lung cancer turn out to be true, there are many other unpleasant diseases, like emphysema, which damage the quality of life and which can be prevented by stopping smoking."
A large-scale study published in 1994 found that cigarettes would eventually kill one in two smokers.
M ore than half the 20,000 heart attacks each year in people under 50 e been attributed to cigarettes — with smokers in their 30s and 40s: times more likely to suffer a heart attack than non-smokers. One of the most powerful men m the tobacco industry admitted publicly for the fist time that smoking was lethal and nicotine was an addictive drug.
Geoffrey Bible, chairman and chief executive of Philip Morris, testified in Florida lawsuit that cigarette smoking may have caused 100,000 deaths.