Toenails and Lung Cancer

We’ve known about the causal link between smoking and lung cancer for 55 - 60 years, but there’s a new twist that helps address the risk run by people exposed to second-hand smoke.  It concerns the presence of nicotine in the body as a possible biomarker for lung cancer risk.  The relevant study is posted online in the American Journal of Epidemiology.   

The Health Professionals Follow-Up Study enrolled about 33,700 medical professionals 25 years ago.  Many of them donated toenail clippings, which have been preserved at room temperature.  San Diego researchers decided to see if toenail nicotine levels were associated with lung cancer risk.  There were 210 men with lung cancer in the study; a further 630 were carefully selected as matched controls.

The average toenail nicotine level was 0.95 nanogram/mg in men with lung cancer, compared with 0.25 nanogram/mg in the controls. When the men were classified into 5 groups (or quintiles), according to their toenail nicotine levels, the risk for lung cancer for the highest 20% was 10.5-times greater than that for the lowest 20%.

If the amount of smoking (number of pack-years) was used to adjust the risk levels, the risk in the highest toenail nicotine quintile (20%) was 3.57-times greater than that for the lowest quintile. This means the toenail nicotine was a strong predictor of lung cancer independent of smoking history, suggesting that exposure to smoke, as well as actual smoking, can be responsible for increasing the risk of lung cancer.

This study shows that whether you are a smoker or a non-smoker exposed to second-hand smoke, you are at increased risk of acquiring lung cancer. As one researcher said, “evidence of exposure to smoke can be found throughout the entire body – even the tip of the toes – and this exposure increases the risk of lung cancer”.  That says it all.