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    How Old Are You Inside? Blood Test May Tell

    Researchers Report Development of a Blood Test to Check People's 'Molecular Age'

    Molecular Age Results continued...

    Exercise was linked to lower levels of p16. It's not yet clear if exercise lowers p16 levels, or if people who exercise have low p16 levels for some other reason. Perhaps those people have diet habits that keep their p16 level low, Sharpless says.

    "I really wouldn't want to make the mistake that has been made recurrently in epidemiologic association studies that try and place some causal relationship between the two, other than just note that there's a strong relationship that's reproducible," he says.

    BMI (body mass index) wasn't related to p16 after the researchers took age into account. That finding surprised Sharpless.

    "I would have thought that people who were thinner would have lower p16 for their age. That wasn't true," Sharpless says. "One could infer from that that body mass is not a great predictor of fitness ... it just turned out to be a bad marker of molecular age for us."

    Test's Uses

    Sharpless sees several possible uses for the p16 blood test.

    For instance, he says the test could be used as a way to determine which patients are eligible for certain medical treatments that have age limits. "There are some really healthy 70 year olds out there who are very fit and can have fairly aggressive therapies, and then there are some people who are two decades younger who are not so fit, who are sort of prematurely old," Sharpless says.

    He also sees the p16 test as a tool for researchers to explore whether anti-aging candidates -- such as resveratrol or green tea -- really delay aging.

    "I jog and try and drink green tea or red wine," Sharpless says. "But wouldn't you like to know, if you're doing that stuff for decades at a time, that it's working? Wouldn't you like some solid evidence that these sorts of wellness behaviors are really doing what you're intending them to do?"

    Sharpless worries about how the test might be used by health insurance companies or employers.

    "I think we have to be careful about how you would apply such a marker," he says. "This is an issue we're going to have to face in the future as a society."

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