Forget the candles on your birthday cake; there's a good chance your biological age could be younger — or older — than your chronological age.

Researchers have defined a signature of 150 RNA genes that indicate healthy aging. Using a "healthy age gene score" derived from that data, they are able to calculate whether people are more at risk of age-related disease, such as Alzheimer's and osteoporosis. These researchers say biological age can differ substantially from true age, and it's a better indicator of a person's health.

"We use birth year, or chronological age, to judge everything from insurance premiums to whether you get a medical procedure or not," said lead author James Timmons from King's College London in a statement. "Most people accept that all 60 year olds are not the same, but there has been no reliable test for underlying 'biological age'."

In the new study, published in the journal Genome Biology, researchers analyzed genetic material from healthy 65-year-olds to discover the genes that showed signs of healthy aging.

The researchers then used this healthy age gene score to follow a group of 70-year-old subjects. Their theory tested out. Those with higher scores had better overall health, including two key indicators of longevity, cognitive function and kidney function.

Specifically, they found that people with Alzheimer's disease had lower gene scores.

"This is the first blood test of its kind that has shown that the same set of molecules are regulated in both the blood and the brain regions associated with dementia, and it can help contribute to a dementia diagnosis," said Timmons. "This also provides strong evidence that dementia in humans could be called a type of 'accelerated ageing' or 'failure to activate the healthy ageing program'."

Because early intervention is so critical with Alzheimer's, researchers say this healthy age gene score can be used to help decide which patients are entered into preventive clinical trials long before clinical symptoms appear.

Assuming the study results hold up, having a diagnostic tool to determine Alzheimer's risk would be tremendously useful, said Eric Topol, a cardiologist/geneticist at Scripps Health, in an interview with The San Diego Union-Tribune.

"They took a pretty systematic approach, but it's going to require considerably more work," Topol said. "It's more in the discovery phase and they have to validate it ... What they're hunting for is a worthy hunt; whether they have it, it's still very preliminary."

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.