UCLA geneticist Steve Horvath led a team of 65 scientists in seven countries to record age-related changes to human DNA, calculate biological age and estimate a person's lifespan. A higher biological age—regardless of chronological age—consistently predicted an earlier death.

The findings are published in the journal Aging.

Drawing on 13 sets of data, including the landmark Framingham Heart Study and Women's Health Initiative, a consortium of 25 institutions analyzed the DNA in blood samples collected from more than 13,000 people in the United States and Europe.

Applying a variety of molecular methods, including an epigenetic clock developed by Horvath in 2013, the scientists measured the aging rates of each individual. The clock calculates the aging of blood and other tissues by tracking methylation, a natural process that chemically alters DNA over time. By comparing chronological age to the blood's biological age, the scientists used the clock to predict each person's life expectancy.

"We were stunned to see that the epigenetic clock was able to predict the lifespans of Caucasians, Hispanics and African-Americans," said first author. "This rang true even after adjusting for traditional risk factors like age, gender, smoking, body-mass index, disease history and blood cell counts."

The group's findings, however, don't bode well for everyone.

"We discovered that 5 percent of the population ages at a faster biological rate, resulting in a shorter life expectancy," author said. "Accelerated aging increases these adults' risk of death by 50 percent at any age."

For example, two 60-year-old men, Peter and Joe, both smoke to deal with high stress. Peter's epigenetic aging rate ranks in the top 5 percent, while Joe's aging rate is average. The likelihood of Peter dying within the next 10 years is 75 percent compared to 60 percent for Joe.

The preliminary finding may explain why some individuals die young – even when they follow a nutritious diet, exercise regularly, drink in moderation and don't smoke. "While a healthful lifestyle may help extend life expectancy, our innate aging process prevents us from cheating death forever," author emphasized. "Yet risk factors like smoking, diabetes and high blood pressure still predict mortality more strongly than one's epigenetic aging rate."

The precise role of epigenetic changes in aging and death, however, remains unknown, said coauthor.

"Do the epigenetic changes associated with chronological aging directly cause death in older people?" said the co-author. "Perhaps they merely enhance the development of certain diseases—or cripple one's ability to resist the progression of disease after it has taken root. Future research is needed to address these questions."

Larger studies focused only on cases with well-documented causes of death will help scientists tease out the relationship between epigenetic age and specific diseases, he added.

The University of California has applied for a provisional patent on the epigenetic clock.