Why do some people lead a perfectly healthy lifestyle yet still die young? A new international study suggests that the answer lies in our DNA. UCLA geneticist Steve Horvath led a team of 65 scientists in seven countries to record age–related changes to human DNA, calculate the biological age of blood 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. “Our research reveals valuable clues into what causes human aging, marking a first step toward developing targeted methods to slow the process,” said Horvath, the principal investigator and a professor of human genetics and biostatistics at the David Geffen School of Medicine at UCLA and Fielding School of Public Health. 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. 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.