Toenails Tell the Tale of Women, Smoking and Heart Disease
June 12, 2008 - The higher the level of nicotine in the toenails, the higher the risk of coronary heart disease (CAD), no matter the number of cigarettes smoked or level of exposure to second hand smoke, said researchers from University of California, San Diego, School of Medicine, who ran the study in collaboration with colleagues from Harvard University.
Study results were published in the online edition of the American Journal of Epidemiology, April 2008, and also appear in the June print edition.
“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 analyzed toenail clippings from 62,641 women between the ages of 36 and 61 years collected for the Nurse’s Health Study cohort. Between 1984 and 1998, 905 women were diagnosed with heart disease and, on average, those diagnosed with heart disease had double the level of nicotine in their toenails than women without heart disease.
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.
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.
A limitation of this study is the declining exposure of nonsmokers to secondhand smoke and the decline in active smoking nationwide. The measured exposure in 1982 might have misclassified exposure in later years. “If anything, such decline in exposure will underestimate the risk we found between toenail nicotine levels and heart disease,” said Al-Delaimy. “That means the risk is possibly even higher than reported.”
This study was funded by grant 12548 from the Flight Attendants Medical Research Foundation.
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