But many experts hold that until large, careful studies are done over many years, scientists won't be able to put firm numbers on risk factors for disease or longevity. For starters, there's no consensus yet on how best to measure telomeres or serve up the results. Indeed, two of the companies that have developed tests — Telome Health and Life Length, based in Madrid — will provide different types of results. Life Length says its $700 blood test, which is now available to consumers in the United States, compares your actual and "biologic" ages by measuring the percentage of short telomeres. Telome Health, by contrast, uses your saliva to measure the average length of your telomeres and compare that to others. (Company representatives say they haven't yet set a price for the test.)
Another issue: People are born with varying lengths of telomeres, making it difficult to get a handle on relative shrinkage, says Peter Hornsby, a physiology professor at the Barshop Institute for Longevity and Aging Studies at the University of Texas Health Science Center in San Antonio. "We have no evidence that telomere length is a health predictor — there is always a possibility that this could change in the future but I do not see this happening," he wrote in an email.
Currently, no one knows with any certainty just what constitutes a normal-length telomere at different ages, in different types of people, says Greider. There's simply too much variation within age groups. "If you sent me a telomere sample from a 40-year-old I couldn't tell whether that person was 15 or 70," she says.
And despite the link between telomeres and age-related diseases, only a very small segment of the population has telomeres so short that it's possible to say for certain they have a high risk of a disease, she says. "We have strong data from families with inherited short telomeres showing they are at risk for pulmonary fibrosis and bone marrow failure," she says. But 99 percent of people are not in that group. "Right now we can't tell that 99 percent very much," she says.
Moreover, while science points to a link between short telomeres and disease, it hasn't shown that one causes the other, says Judith Campisi, an expert on aging and a professor at the Buck Institute for Research on Aging in Novato, Calif. She's also concerned that telomere tests could provoke needless anxiety.
Stephen Matlin, Life Length's chief executive officer, says the company's test results include comparisons with people of similar ages and backgrounds, along with information about the test's limitations.
Studies that measure telomeres of large groups of people of various backgrounds and ages will be very important to advancing our understanding of these structures, Greider says. But this work should be done in a scientific setting where the findings are shared and discussed, and where one study builds on another to add to our total knowledge.
Charlotte Huff is a freelance writer in Fort Worth, Texas, who reports on medical issues.
Also of interest: Slow aging and prevent disease.