Most drug tests use saliva or urine, but researchers from the University of California-San Diego Medical Center and Harvard School of Public Health found that examining men’s toenail clippings was the most reliable way to figure out how much nicotine they had in their body — and their risk of developing lung cancer.
Why toenails? Because they grow slowly and accumulate a more stable level of nicotine than urine or saliva.
The current study found that men who had high levels of nicotine in their toenails had 3.57 times the risk of developing lung cancer of men who had low levels of nicotine in their clippings — regardless of how much or how often they smoked. In fact, researchers found, more than 10% of the men with the highest levels of nicotine in their nails never smoked cigarettes at all.
The toenail test may be more effective than using questionnaires about smoking history, according to the researchers, as MSNBC reported:
Studies that only ask people how much they smoke might misjudge the amount of nicotine people actually inhale — either because people fudge a little when they answer, or because some may smoke fewer cigarettes than others but inhale more deeply, taking in more tobacco carcinogens.
The researchers used data on male smokers between, aged 40 to 75, who gave samples of toenail clippings for nicotine analysis in 1987 as part of the Health Professionals Follow-up Study, involving 33,737 total participants. The researchers split the samples into two groups of smokers: 210 samples from men who developed lung cancer over a 12-year period and 630 from men who never got the disease. After adjusting for smoking behavior, the researchers found that the men in the highest quintile of nicotine content in toenail clippings were 3.57 times more likely to have developed lung cancer than men in the lowest quintile.
“[T]he toenail nicotine biomarker was found to be a strong predictor of lung cancer independent of smoking history, suggesting that the adverse effects of cigarette smoke may be underestimated in studies based on smoking history only,” wrote researchers, Dr. Wael K. Al-Delaimy and Dr. Walter C. Willett.
The same team has previously used nicotine levels in toenail clippings to gauge women’s risk of heart disease.