Searching for Meaningful Markers of Aging

David Stipp in The New York Times:

How fast are you aging?

Age…In a 2010 study, Dr. Miller and colleagues analyzed medical records of 4,097 women, collected over two decades beginning when they were in their 60s, to sift out 13 factors that best predicted future mortality from different causes. Oddly, contrast sensitivity — as measured by a test of the eye’s ability to pick out very lightly shaded images on white backgrounds — was among the most predictive of the 377 factors evaluated, as was the number of rapid step-ups on a low platform that the subjects could complete in 10 seconds. Taken together, the 13 factors “characterize the clinical presentation of healthy aging” in older women, the study concluded. More recently, novel technologies that can detect thousands of age-associated molecular changes in cells have come to the fore in the biomarker hunt.

Earlier this year Dr. Zhang and his colleagues in San Diego reported that a kind of molecular aging clock is embedded in our genomes whose speed can be measured via blood testing. The moving parts of the clock consist of chemical tags on DNA molecules that control whether genes are active in cells. The researchers found that the patterns of the tags, called epigenetic markers, predictably change with age. In a study published in January in Molecular Cell, the scientists scrutinized around 485,000 of these tags in blood cells of 656 people aged 19 to 101. Some 70,387 tags were predictive of chronological age, the scientists found. Collectively these tags spell out a “signature for age” that is “largely not changed by disease or ethnic background,” said Ronald Kohanski, an expert on biomarkers of aging at the National Institute on Aging. That means these markers may be less muddied by confounders than other factors tied to aging. Of the markers, 71 most indicative of chronological age were selected to measure the speed at which people are growing old. That was calculated by comparing a subject’s epigenetic tags to the norm for his or her age — a 40-year-old whose pattern closely resembled the typical one for 50-year-olds, for example, would apparently be aging 25 percent faster than normal.

Already the molecular clock has yielded interesting findings. Men appear to age on average 4 percent faster than women, the scientists have found, which may largely explain why women’s life expectancy exceeds men’s by about 6 percent worldwide. And the research has shed intriguing light on cancer: The clock indicated that tumor cells have aged, on average, 40 percent more than normal cells taken from the same patients.

More here.