Five years ago, a critical discovery in the understanding of cellular aging was made by researchers from the University of North Carolina (UNC) at Chapel Hill Lineberger Comprehensive Cancer Center. Through their research, they learned that expression of a key tumor suppressor protein -- p16INK4a - dramatically increases in most mammalian organs with the aging of cells and tissue.

Now, a new study conducted by the same team of researchers has shown that p16INK4a is also present in human blood and is strongly associated with aging and such behaviors as tobacco use and physical inactivity, both of which are known to accelerate the aging process. Moreover, the researchers have been able to develop a simple blood test capable of detecting p16INK4a, which is present in T-lymphocytes. Their research was based upon two key factors: blood taken from 170 healthy human volunteers and a questionnaire that the participants completed, providing information about past and current health status and behaviours. As the scientists discovered, the expression of p16INK4a increased exponentially with age, and that those increased levels were independently associated with tobacco use, physical inactivity and with biomarkers of human frailty.

"This is a major step toward a practical tool to clinically determine a person's actual molecular age, as opposed to just their chronological age," emphasizes UNC Lineberger member Norman Sharpless, M.D., the senior author of the study and associate professor of medicine and genetics at UNC's School of Medicine. "We found a very weak correlation between the biomarker and obesity as measured by body mass index, despite other data suggesting that caloric restriction slows aging. The data suggest the possibility that reduced exercise may actually be worse with regard to molecular age than a higher BMI," says Dr. Sharpless, who expressed surprise about the findings.

"Although we don't know whether this test is a good reflection of cellular age in all types of human tissues, we believe it is a first step toward a better understanding of issues like the suitability of organs for transplantation, how well patients are likely to recover after surgery or the future toxicity of chemotherapy for cancer patients," he adds. Study findings are being published in the journal Aging Cell.