Measuring nicotine levels in clippings found men with the highest readings were more than three times more likely to get cancer than those with the lowest.
　　Because toenails grow so slowly – at 1cm a year – they provide vital information on long-term exposure to cigarette smoke.
　　The findings, by experts at the University of San Diego in California, could pave the way for doctors to screen for lung tumours.
　　Toenails not only identify which smokers are most at risk but also which non-smokers, says the study in the American Journal of Epidemiology.
　　This means it provides clues to the damaging effects of passive smoking.
　　The researchers took clipping samples from 850 men and followed them for more than 12 years to see who developed lung cancer.
　　They estimated that those with the highest nicotine levels were three-and-a-half times more likely to suffer cancer 12 years later than those with the lowest.{
　　Lung cancer kills just under 30,000 people a year in England and Wales and smoking causes around 90 per cent of cases.
　　It's estimated that people who smoke more than 20 cigarettes a day are 20 times more likely to get it than non-smokers.
　　Figures released earlier this week showed rates have more than doubled for women over 60 since the mid-1970s.
　　The disease now strikes 190 in every 100,000 women, up from 88 per 100,000 nearly 30 years ago.
　　Experts blame the fact that smoking peaked in women during that period. However, disease rates among men have fallen because smoking was already declining in popularity by the 1970s.
　　Toenails grow around one centimetre a year so can give vital clues on long-term exposure to cigarette smoke
　　Toenail samples were taken from each volunteer at the beginning of the experiment in 1987 and analysed for nicotine levels.
　　The men were then followed for up to 12 years to see which ones developed lung cancer.
　　The results showed the lung cancer victims had average nicotine levels 12 years earlier of around 0.95 nanogrammes per milligramme.
　　But those free of cancer had just 0.25ng per milligramme.
　　Scientists estimated that those with the highest nicotine levels were three-and-a-half times more likely to suffer cancer than those with the lowest.
　　In a report on their findings, researchers said the toenail test showed the hidden risks for non-smokers.
　　More than ten per cent of men with the highest levels of toenail nicotine were never smokers.
　　The study shows toenail nicotine levels provide a biomarker that can predict the risk of lung cancer independent of reported smoking history.

责编:蒲公英