A new way to measure how humans age suggests that Latinos withstand life's wear and tear better than non-Latino Caucasians, and that they may have their Native American ancestors to thank for their longer lives.
Hispanics in the United States live an average of three years longer than whites. The average life expectancy for Hispanics is 82 versus 79 for whites, the U.S. Centers for Disease Control and Prevention says.
A 2013 study in the American Journal of Public Health found that regardless of age, healthy Hispanic adults face a 30% lower risk of early death than other racial groups.
Those findings emerge from an intriguing effort to devise a genetic clock — a standard measure of age more revealing than birthdays, walking speed, wrinkled skin or twinkly eyes. By doing so, researchers hope to glean why some people die young while others live long, to understand what chronic diseases have to do with aging, and to predict and increase patients' life spans. A reliable measure of biological age could also set a standard by which to judge the effectiveness of anti-aging therapies.
Steve Horvath, professor of human genetics at the David Geffen School of Medicine at University of California, Los Angeles, has devised a measure of aging that reflects the activity level of the epigenome, the set of signals that prompts an individual's genes to change their function across the lifespan in response to new demands.
Horvath's epigenetic clock captures a key feature of aging that as we grow older, there are complex but predictable changes in the rate at which our genes are switched on and off by a chemical process called DNA methylation. To arrive at a single measure of a person's biological age and then compute his or her speed of aging, Horvath has proposed to measure epigenetic activity at 353 sites in a person's genome.
Earlier efforts to devise an epigenetic clock suggested that biological age, and the speed of aging, not only differ among populations and from person to person. The tissues in each of us may age at different rates. That may explain, for instance, why some organs and tissues are more vulnerable than others to such age-related diseases as cancer.
The new study, published in the journal Genome Biology, set out to refine and test that clock. To do so, Horvath and his colleagues analyzed 18 sets of DNA samples from blood, saliva and lymphoblastoid samples collected from 5,162 participants in a wide range of studies.
And the finding isn't impacted by lifestyle factors that could affect health and longevity, say the researchers, as they'd accounted for things such as diet, socioeconomic status, and education levels in their research.
One example given by the team describes how, after menopause, the epigenetic clock suggests that Latino women's bodies are actually 2.4 years younger in biological terms than non-Latino women of the same calendar age.
And it is this invisible physical youthfulness that the researchers think helps Latinos fight off chronic diseases comparatively better as they get older at least to a significant extent when compared to non-Latinos.
"We suspect that Latinos' slower ageing rate helps neutralise their higher health risks, particularly those related to obesity and inflammation," says Horvath. "Our findings strongly suggest that genetic or environmental factors linked to ethnicity may influence how quickly a person ages and how long they live."
Those participants included not only black, white and Latino Americans but also Han Chinese, members of the Tsimane Amerindian tribe in South America, and two separate groups of Central Africans, rain-forest-dwelling hunter-gatherers and agrarians living in grasslands and open savannas.
The Tsimane, an indigenous people who forage and cultivate crops in the lowlands of Bolivia, offer an especially good test of the epigenetic clock, constantly bombarded with bacterial, viral and parasitic infections, the Tsimane typically experience high rates of inflammation, which has widely been seen as a marker for aging.
But they rarely show risk factors for heart disease or develop Type 2 diabetes as they age, and obesity, high blood pressure and problematic cholesterol are virtually nonexistent.
The epigenetic clock found that the Tsimane aged even more slowly than Latinos. The biological clock calculated the age of their blood as two years younger than Latinos and four years younger than Caucasians.
But that finding was despite strong evidence that, over age 35, a Tsimane's immune system was close to exhausted and his inflammation levels "make him look like a 90-year-old," said Horvath.
The researchers also found that blood and brain tissue ages faster in men than in women. This result jibes with the fact that women commonly live longer than men.
A biological clock like the one Horvath created would be very useful for researchers once it has been confirmed as accurate, said Steven Austad. He's chair of biology for the University of Alabama at Birmingham and scientific director of the American Federation for Aging Research.
Such a clock could rapidly compress the time it takes to complete clinical trials for drugs with the potential for slowing aging, for example -- allowing what normally would be a five-year or 50-year study to be completed in a matter of months, Austad said.
Unfortunately, aging is a complex process and has resisted previous attempts to quantify it. Researchers looking to confirm this potential biological clock should test it on lab animals, where they can account for other factors that also influence aging.