New blood test tells how long you have to live: Does it work?

(CBS) How long will you live?

That question may no longer be an idle one, as scientists say they've come up with a simple blood test that reveals your "biological age," permitting a reasonable estimate of just how soon you're likely to encounter the grim reaper.

The over-the-counter test is scheduled to go on sale in Britain later this year, the Independent reported. It purportedly works by measuring the length of one's telomeres. Those are the cap-like molecular structures on the tips of the chromosomes that scientists say are closely linked to one's biological age - and the shorter they are, scientists believe, the nearer one is to death.

"We know that people who are born with shorter telomeres than normal also have a shorter lifespan," the test's developer, Maria Blasco of the Spanish National Cancer Research Center in Madrid, told the paper. "We know that shorter telomeres can cause a shorter lifespan."

The $700 test should tell biological age to "within a decade," Dr. Jerry Shay, professor of cell biology at University of Texas Southwestern Medical Center in Dallas and a consultant to Life Length (the company that plans to offer the test), told CBS News in an email. He said the test - which is available now to Americans who want to send a blood sample to Spain - would likely be of great interest to cosmetic and pharmaceutical companies looking to develop new products as well as to ordinary people.

"If you are under a lot of stress and your telomeres are shorter compared to your age bracket, there is evidence that behavior modification may be able to reverse some of this loss," Dr. Shay wrote." It is similar to a cholesterol or blood pressure test where similar behavioral modifications can reduce these risk factors." And, he said, scientists are looking for substances that might slow or even reverse the shortening of telomeres - possibly opening the door to antiaging therapies.

But not everyone is as sanguine as Dr. Shay. In addition to concerns about how people will react to finding out how "old" they are, some scientists worry that telomere testing will be hijacked by companies peddling unproven age-reversing therapies. There's also the possibility that insurance companies would use the information to raise rates for customers deemed to be older than the calendar suggests.

Some experts are dubious of the whole idea of telomere testing.

"We cannot tell how old a person is by looking at their telomeres," Carol Greider, a geneticist who studies telomeres at Johns Hopkins University School of Medicine in Baltimore, told msnbc.com. The bottom line, she told the Boston Herald, is that "the science isn't there yet."