Certain populations live longer than others: Women tend to outlive men and Hispanics have lower mortality rates than other ethnic groups. But the mystery is why. There are many social and health theories that have tried to explain it, but in an attempt to offer a definitive answer to the question, Steve Horvath, a professor of human genetics at the David Geffen School of Medicine at UCLA, went straight to the source: our DNA.
I called up Horvath after he graciously agreed to explain his very complicated study on what he previously termed the "epigenetic clock" like I was four years old. Horvath is German, and over the phone, his thick accent made his recent findings about how genetic markers in our blood and cell tissues can measure our age—and how those markers can differ across sex and ethnicity—sound even more like mad science.
"It was understood that different ethnic and racial groups have different risks of mortality, or that some people have a longer lifespan than others," he told me. "But how do you really measure that aging? Before our study, there were very, very few studies that looked at the aging rate. There was a technical reason for this: There were very few measures of aging."
That's where Horvath's epigenetic clock, a molecular measure of aging, comes in. Horvath found that our DNA, while it doesn't change, can tell us our age through the epigenetic modifications that it undergoes over time. "There's something called DNA methylation, which is a chemical modification of the DNA molecules. That's what we're looking at. As we age, some parts of our DNA gain methylation, and some parts lose methylation. By looking at all of these changes over time, one can actually very accurately measure somebody's age. This is the first study that uses this highly accurate measure of biologic age," Horvath explained. "If you sent me your blood I could tell you your age," he added.
There's no doubt that men are worse off than women.
The study analyzed two blood measures that are markers of age in 6,000 people from various ethnic groups—intrinsic epigenetic age acceleration (IEAA), which can't be influenced by lifestyle factors (like smoking or drinking) and extrinsic epigenetic age acceleration (EEAA)—which were further subdivided by sex. What Horvath found was that Latinos have lower IEAA than other groups, meaning they fundamentally age more slowly. Latina women in the study, for example, were 2.4 years younger than non-Latino women of the same age when measured by the epigenetic clock.
"We can show that Hispanics age more slowly independent of changes in the blood cell," he said. However, Latino men and women are at higher risk for diseases like obesity, chronic liver disease, and diabetes—or, in other words, their EEAA is high. Horvath hypothesizes that the slower aging rate of Hispanics helps neutralize their higher health risks.
The study also found that, on average, women of all ethnicities aged more slowly than men. "There's no doubt that men are worse off than women. That is in every ethnic and racial group. We looked at several tissue groups and blood and their saliva. Being a man is really bad news."
Horvath is planning to further study the molecular mechanism that protects Latinos from aging and causes women to age slower than men.
I asked Horvath if this research could set the stage for aging interventions. I thought about those experiments with mice, where an old mouse gets strapped to a young mouse and becomes more youthful using its blood, and imagined a strange future: Would people be lining up to get Hispanic blood infusions, with Peter Thiel leading the way?
Luckily, Horvath thinks we're pretty far off from that, though he was amused by the thought. "Theoretically that might be possible, but I just don't have any idea," he laughed. "The great hope is that maybe we will find certain drugs that affect the epigenetic aging rate. But we don't have any interventions at this point."