Discussing your toenails may not be an intriguing conversation starter, but as it turns out, they say a lot about your current health status. Recently, a study conducted by researchers at UC San Diego and Harvard found that toenails harbor nicotine levels that could indicate your lung cancer and heart disease risk, even if you aren’t a smoker.
Let’s say you’re sitting in a club or restaurant next to friends who are smoking. The smoke being exhaled or exiting the end of a lit cigarette and circulating in the room contains scores of chemicals that get stored as biomarkers in your nails, hair and skin. Even though you aren’t a smoker yourself, as you breathe in the smoke-filled air you are passively smoking. This is also known as secondhand smoke.
Wael K. Al-Delaimy, MD, PhD, chief of the global health division at UC San Diego, a member of the Cancer Center, and co-investigator of this study was looking for a way to measure passive smoke exposure. At first he was measuring nicotine exposure in hair when he learned his Harvard co-author had a very large collection of toenail clippings.
Since hair and toenails are formed from the same kind of tissue, Al-Delaimy decided to take advantage of the collection for this study. According to Al-Delaimy, there are clear advantages to studying toenails.
"They can be stored at room temperature for years and because they grow slowly—only about 1 centimeter every nine to 12 months— toenails give a true nicotine exposure during the past year.”
While the current study analyzed toenail clippings of men--210 with lung cancer and 630 without lung cancer for a comparison--Al-Delaimy has also shown that toenail nicotine levels accurately predict the risk of heart disease in women. In a previous study, women with the highest nail nicotine levels were shown to have a 42 percent higher risk of heart disease compared to those women with the lowest level.
Heart disease is the leading cause of death in the United States for men and women of all ages; Lung cancer is the leading cause of cancer-related death in the United States for men and women, according to the Centers for Disease Control.
The toenail clippings were gathered as part of the 1987 Health Professionals Follow-up study where most of the 33,737 participants donated samples. The current findings are published early online in the March 2011 edition of the American Journal of Epidemiology.
For this study, 20 percent of the toenails containing the highest amounts of nicotine identified men with the highest risk of lung cancer. These men were 10.5 times more likely to have lung cancer than the 20 percent of men with the lowest nicotine levels.
The researchers went further to compare men at similar levels of cigarette use. Among smokers, those with the most nicotine in their toenails were more than 3.5 times more likely to get lung cancer than those with the least toenail nicotine.
"We knew tobacco was harmful, but we are now learning it is even more harmful than we had previously measured," Al-Delaimy said. "We are getting a better estimate of the true risk of tobacco's lung effects and this could be applied to other disease outcomes such as coronary heart disease, too."
The researchers showed that toenail nicotine levels are closely linked to smoking status six years prior to collection of clipping samples.
“While toenails are unlikely to form the basis of a screening test, these results show that chemicals in tobacco smoke can affect many other parts of the body beyond the mouth and lungs,” said Ed Yong, Cancer Research UK’s head of health evidence and information in an email statement. “Tobacco can cause cancers in many organs such as the kidney, pancreas, liver, stomach, bladder and cervix.”
Lynette Summerill is an award-winning writer who lives in Scottsdale, Arizona. In addition to writing about cancer-related issues for EmpowHER, she pens Nonsmoking Nation, a blog following global tobacco news and events.