If we cannot accurately measure the progression of aging, then how do we establish whether a therapy under development meaningfully impacts aging? Animal studies will always precede human trials, and the necessary years will have been taken to measure changes in life span in short-lived species in the laboratory, but it is obviously out of the question to evaluate the effects on people by the wait-and-see method. A popular science piece here looks at the importance of the search for reliable ways to measure aging:
Don't look to online calculators of "biological age" for an answer. Those focus mainly on risk factors for diseases, and say little about normal aging, the slow, mysterious process that turns children to codgers. In fact, scientists are still hunting for biological markers of age that reliably register how fast the process is unfolding. Seemingly obvious candidates won't do. Wrinkles, for example, often have more to do with sun exposure than aging. Markers like age-related increases in blood pressure are similarly problematic, often confounded by factors unrelated to aging.
But recently researchers have identified some particularly good indicators of time's largely hidden toll on our bodies and how fast it's increasing. Experts on aging generally agree that acceptable biomarkers of aging should foretell the remaining life span of a middle-aged person more accurately than chronological age does. Further, they should offer a consistent picture of biological age. "Do those 50-year-olds with the best retention of immune function also tend to have the least cataracts, good sense of smell, least osteoporosis, lowest blood pressure and best memory?" Proposed biomarkers of aging haven't yet convincingly cleared these hurdles. But some provocatively telling ones have come to light.
Earlier this year [researchers] 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. 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. Collectively these tags spell out "a signature for age that is largely not changed by disease or ethnic background." That means these markers may be less muddied by confounders than other factors tied to aging.