Telltale toenail nicotine predicts heart problems

NEW YORK (Reuters Health) - Analyzing the nicotine content of toenail clippings can help gauge a woman's heart disease risk, a new analysis of findings from the Nurses' Health Study shows.

Toenail analysis "could become a useful test to identify high-risk individuals in the future, especially in circumstances when smoking history is not available or is subject to bias," Dr. Wael K. Al-Delaimy of the University of California in San Diego and colleagues say in the American Journal of Epidemiology.

Biomarkers of cigarette smoke exposure now used, such as the amount of cotinine (a nicotine breakdown product) in urine or saliva, only reflect exposure within the past few days, the researchers note. Because toenails grow slowly, they add, they may offer a longer-term, more stable estimate of a person's total level of exposure to tobacco smoke.

To investigate, the researchers correlated the nicotine content in toenail clippings collected in 1982 for 62,641 women participating in the Nurses' Health Study to the risk of being diagnosed with heart disease between 1984 and 1998.

The women in the top fifth for toenail nicotine content were thinner, less active, heavier drinkers, and more likely to have high blood pressure or diabetes, as well as a family history of heart attack, compared to those with less nicotine in their toenails, Al-Delaimy and colleagues found.

Also, the 905 women who had been diagnosed with heart disease had twice as much nicotine in their toenails, on average, as similar women without heart disease.

After the researchers adjusted for other risk factors, they found that women in the top fifth for toenail nicotine had nearly four times the risk of heart disease compared to those in the bottom fifth.

The findings suggest that measuring nicotine levels in the toenails "may improve the assessment of exposure and therefore our understanding of tobacco-related illnesses," the researchers conclude.

SOURCE: American Journal of Epidemiology, June 1, 2008.