By reading a "signature" based on 150 of a person's genes, researchers can determine the individual's biological age, which may be different from his or her chronological age, according to a new study.

Moreover, a person's biological age is a better measure for determining a person's health than is chronological age, these researchers say. In the study, people's biological age was more closely tied to their risk of age-related diseases, such as dementia and osteoporosis, than was their chronological age.

"Most people accept that all 60-year olds are not the same," James Timmons, a professor of precision medicine at King's College in London and the lead author on the study, said in a statement. But a person's chronological age is still used to determine everything from the individual's insurance premiums to whether he or she needs certain medical procedures, he said.

In the new study, published today (Sept. 8) in the journal Genome Biology, the researchers analyzed genetic material from healthy 65-year-olds, looking for genes that indicated the participants were staying healthy as they aged. [Extending Life: 7 Ways to Live Past 100]

The scientists found 150 genes that they used to calculate what they called a person's "healthy age gene score."

To verify that these scores did indeed track with people's health, the researchers tested out their method in a separate group of participants, who were all 70 years old. The scientists found that higher scores were indeed associated with better health, including better cognitive health.

In particular, they found that patients diagnosed with Alzheimer's disease had lower healthy age gene scores.

"This provides strong evidence that dementia in humans could be called a type of 'accelerated aging' or 'failure to activate the healthy aging program,'" Timmons said.

It unclear, however, whether the healthy age gene score could be used to predict whether a person will develop Alzheimer's disease, the researchers wrote in the study.

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That's "the real Holy Grail," said Keith Fargo, director of scientific programs and outreach at the Alzheimer's Association, who was not involved in the study, "a blood test that tells you 10 years in advance if you're going to have Alzheimer's."

Still, the results of the study are valuable, Fargo told Live Science. The researchers were able to look at people who were all the same age, and determine who had healthy cognition and who didn't, he said. That means the test could help determine what genetic differences separate a 70-year old with Alzheimer's and a 70-year old without the disease, he said.

Further researcher into those 150 genes may also give clues about what causes Alzheimer's, Fargo said.

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