The level of nicotine in womens’ toenails can predict the risk of coronary heart disease, say researchers from the University of California, San Diego.
By analyzing the nicotine levels in the toenails of more than 60,000 women, the researchers found that those who had suffered heart disease had on average twice the levels of nicotine in their toenails than women without heart disease.
“Using toenail nicotine is a novel way to objectively measure exposure to tobacco smoke, and ultimately, to increase our understanding of tobacco-related illnesses,” explained Wael Al-Delaimy, Ph.D., Department of Family and Preventive Medicine, UC San Diego School of Medicine. “It has advantages over using other biomarkers and could become a useful test to identify high-risk individuals in the future. This would be especially helpful in situations where smoking history is not available or is biased.”
Researchers found no difference in age, body mass index, aspirin use, or history of high cholesterol corresponding to the toenail nicotine levels. Women with the highest toenail nicotine levels were physically less active, had a lower body mass index, drank a higher amount of alcohol, and were more likely to have histories of high blood pressure, diabetes, and family history of heart attack than women with lower levels.
Why toenails? The toenails have an advantage over other existing biomarkers of smoking because they grow more slowly. The levels detected in the nails represent nicotine taken up from blood by nails during growth. The slow growth rates of toenails provide a more stable estimate of average exposure, which is most relevant for illnesses related to tobacco smoke, such as heart disease. Using toenail samples in epidemiological studies is also an attractive concept because they’re easy to collect and store for relatively low cost.
The study was conducted by researchers at University of California, San Diego, School of Medicine, in collaboration with colleagues from Harvard University, and published in the April, 2008 issue of the American Journal of Epidemiology.