New blood tests show that poor populations in urban areas of the United States are actually aging faster at the cellular level than others, thanks to chronic stress connected to income and identity, according to a new study by scientists.

Conducted on a small group of black, white and Mexican adults in three Detroit neighborhoods, the tests were an attempt by scientists to learn what contributed to early aging-related diseases and excessive mortality rates in the urban poor.

The study of racial, ethnic and socioeconomic health inequality involved collaboration between social researchers and cellular biologists at Stanford University. It was based on blood test samples from 239 people, ages 25-64, with a community survey of residents in three Detroit neighborhoods. The blood tests were used to measure telomere length (TL), an indicator of stress-mediated biological aging.

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Previous studies have argued that racial, ethnic and socioeconomic health inequality affect a person's mortality, but many of the studies were based on social research. The Stanford study marks the first collaboration between science and social research that measures telomeres – the caps on chromosomes that protect them from deteriorating.

The telomeres shorten with cell division and over time, as a person ages, they shorten to mark cellular death. Several large studies have argued that telomere length can be affected by stressful life experiences and contribute to early aging, leading to higher risk of infectious and chronic disease like cancer, diabetes and heart disease. Other studies find no significant association between TL and mortality.

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What the Stanford study found was that "the poverty rates for the study participants [in Detroit] were more than double the national rate for blacks and Mexicans and six times the national rate for whites." In Detroit, poverty rates are roughly comparable for whites, blacks and Mexicans at 55.6 percent, 50 percent and 52.3 percent, respectively. They found poor whites had the shortest TL compared to nonpoor whites, and that poor and lower middle class blacks had equivalent TL. But poor Mexicans had longer telomeres than Mexicans with higher incomes.

To account for the different results, the study's author reasoned that poor whites had the shortest TL readings because of an association between short TL and having less than a high school education. Researchers also considered the mass exodus of whites and jobs from Detroit, which led to a growing black population and a white population that then became a minority.

With the city experiencing an overall reduction in taxation, shrinking benefits from labor union membership and public pensions, the effects of urban austerity has taken a significant toll, particularly on whites.

"Lacking the financial resources, social networks, and identity affirmation of the past, remaining Detroit whites may have less to protect them from the health effects of poverty, stigma," said Dr. Arline Geronimus, visiting scholar at the Stanford Center for Advanced Study and lead author of the report.

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"If they're immigrants, then they come with a different cultural background and upbringing that didn't stress that as Mexicans they were somehow 'other' or 'lesser' than other Americans," Dr. Geronimus told The Huffington Post.

"They come with a set of support systems and with a cultural orientation that doesn't undermine their sense of self-worth,” she added. “They then often live in these ethnic enclaves, many of them don't speak anything other than Spanish, and so they're not interacting with Americans who view them as 'other' or who treat them badly. It's not that they're immune to that treatment but they're not as sensitive to it and they also just don't experience it as often."

Geronimus said there are "effects of living in high-poverty, racially segregated neighborhoods -- the life experiences people have, the physical exposures, a whole range of things -- that are just not good for your health."