Why do Hispanic people live longer than other races in the United States? It is a question that experts have been trying to answer for years.

There have been many theories. Perhaps only those who were especially strong and healthy were prepared to emigrate to the United States? Then there's the hypothesis that sick first generation immigrants might have a tendency to return home when seriously ill, thereby disappearing from official US figures.

Now, however, it has been shown that the real answer is much simpler: Latinos just age more slowly.

Taking an age

According to the Centers for Disease Control and Prevention, Latinos in the United States live an average of three years longer than Caucasians, with a life expectancy of 82 versus 79.

At any age, healthy Latino adults face a 30% lower risk of death than other racial groups, according to a 2013 study in the American Journal of Public Health.

US Life expectancy

Image: US Centers for Disease Control and Prevention

"Latinos live longer than Caucasians, despite experiencing higher rates of diabetes and other diseases. Scientists refer to this as the 'Hispanic paradox,'" says Steve Horvath, a professor of human genetics at the David Geffen School of Medicine at UCLA and co-author of the new research on the phenomenon.

“Our study helps explain this by demonstrating that Latinos age more slowly at the molecular level."

The UCLA team used several biomarkers, including an "epigenetic clock", to track a shift in the genome that's linked to aging. Epigenetics is the study of changes to the DNA molecule that influence which genes are active, but don't alter the DNA sequence.

DNA changes

Horvath and his colleagues analysed 18 sets of data on DNA samples from nearly 6,000 people.

The participants represented seven ethnicities: two African groups, African-Americans, Caucasians, East Asians, Latinos and an indigenous people called the Tsimane, who are genetically related to Latinos and live in Bolivia.

When the scientists examined the DNA from blood, which reveals the health of a person's immune system, they were struck by differences linked to ethnicity.

In particular, the scientists noticed that the blood of Latinos and the Tsimane aged more slowly than that of other groups.

"We suspect that Latinos' slower aging rate helps neutralize their higher health risks, particularly those related to obesity and inflammation," said Horvath, who is also a professor of biostatistics at the UCLA Fielding School of Public Health.

The findings, published in Genome Biology, may one day help scientists understand how to slow the aging process for everyone.