So how fast are you ageing?
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 ageing, 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 ageing. Markers such as age-related increases in blood pressure are similarly problematic, often confounded by factors unrelated to ageing.
But recently researchers have identified some particularly good indicators of time's largely hidden toll on our bodies and how fast it's increasing. Developing an easy way to measure biological age will have a wide array of applications in prediction and prevention of age-related diseases, drug discovery and forensics', says Dr Kang Zhang, founding director of the Institute for Genomic Medicine at the University of California.
The quest for truly revealing biomarkers of ageing could tell us a lot about our current and future health. Tracking these indices before and after starting a new diet or exercise program, for instance, might show whether it is actually pushing off your decline and fall. Ageing-rate tests could help scientists evaluate possible anti-ageing compounds in humans without prohibitively long studies.
Experts on ageing generally agree that acceptable biomarkers should predict 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, Dr Richard Miller, a gerontologist at the University of Michigan says. ''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?'' he says.
Proposed biomarkers of ageing haven't yet convincingly cleared these hurdles, he says. But some provocatively telling ones have come to light.
In a 2010 study, Miller and colleagues analysed medical records of 4097 women, collected over 20 years 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 ''characterise the clinical presentation of healthy ageing'' 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.
This year Zhang and his colleagues in San Diego reported that a kind of molecular ageing 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 scrutinised about 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,'' Ronald Kohanski, an expert on biomarkers of ageing at the National Institute on Ageing says. That means these markers may be less muddied by confounders than other factors tied to ageing.
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 ageing 25 per cent faster than normal.
Already the molecular clock has yielded interesting findings. Men appear to age on average 4 per cent faster than women, the scientists have found, which may largely explain why women's life expectancy exceeds men's by about 6 per cent worldwide. And the research has shed intriguing light on cancer: the clock indicated that tumour cells have aged, on average, 40 per cent more than normal cells taken from the same patients.
''We're still far from having a diagnostic for biological ageing,'' Trey Ideker, the chief of genetics at UCSD and a co-author of the study with Zhang says.
But this ''opens the door to an exciting new approach'' to the problem, he says.
If this continuing research pans out, ageing-rate tests may someday be standard in annual physicals, and tracking the results over time would offer unprecedented insights on health risks.
New York Times