A recent study has shown that men with high levels of nicotine in their toenails are 3.5 times more likely to develop lung cancer than those with lower levels of nicotine, regardless of their smoking history.
Toenail clippings were used because they grow slowly and are relatively stable compared to other things such as salivia and urine. With the toenail clippings, there is less chance for error.
In 1986 a health questionnaire was filled out by men and followed up every 2 years. 33,737 men provided toenail clippings. 210 men developed lung cancer between 1988-2000. Clippings were used to to assess men's tobacco exposure over a year. Whats also interesting is that 10% of men who had the most levels of nicotine in their toenail clippings had never smoked. With this group it was possibly from second hand smoke.
This may provide a valuable tool for us in the future. We may not only be checking toenail clippings for fungus and other nail diseases, but also for nicotine levels.
Original article can be found here