An internal "clock" attached to a person's DNA may be a better predictor of age-related memory decline than their actual, chronological age, a new study suggests.
As people age, they tend to gradually lose the ability to process information and retain memories. How quickly and to what extent this happens differs between individuals, meaning that simply looking at a person's chronological age is not enough to predict these changes.
An alternative way to measure aging is to look at chemical tags that latch onto DNA and alter how genes are expressed, without changing the underlying genetic code. Called "epigenetic aging," the addition of these chemical tags happens over time and can be influenced by a person's behavior and environment, differing depending on their stress and diet, for example.
In the new study, published Monday (Oct. 30) in the Journals of Gerontology: Series A, scientists measured the epigenetic "clocks" of 142 adults who were aged between 25 and 65 years old, before asking them to complete daily memory tests on their phones. The authors found that the volunteers' epigenetic ages better reflected how they differed from each other in their cognitive performance than their chronological ages did. The epigenetic ages also captured how each person's performance varied over a short period of time.
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"The study is the first of its kind, to our knowledge, that has examined how these epigenetic aging clocks predict in daily life how well people remember and how quickly they perform mental tasks," senior study author Stacey Scott, an associate professor of psychology at Stony Brook University in New York, told Live Science in an email.
"Previous studies have found this pattern when testing people in the laboratory, but this hasn't been done in everyday life," she said.
To determine the volunteers' epigenetic ages, the researchers looked across their genomes for patterns of DNA methylation — a type of epigenetic modification where molecules called methyl groups stick to DNA. Individuals' epigenetic ages were deemed to be "older" or "younger" depending on methylation levels at key spots in the genome that are known to vary with age.
The researchers then asked the volunteers to complete daily tests that assessed working memory, meaning their ability to temporarily retain small bits of information and use it to complete tasks, as well as their processing speed, or how long it took them to react to and complete the next round of the test.
On average, the volunteers completed around 60 tasks in the two-week study period.
"Because we had people complete these 'brain games' assessments many times," the team was able to examine not only the participants' typical performance but also find out how consistent they were in their scores, Scott said.
On average, the authors found that people whose epigenetic age was judged as older than their chronological age performed worse in both the processing speed and working memory tasks than those whose epigenetic age matched or was younger than their true age. (Perhaps unsurprisingly, chronologically younger people also performed better in the tasks than older volunteers.)
The performance of those with relatively old epigenetic ages was also less consistent between tasks compared with the other volunteers, suggesting that epigenetic age could be a better predictor of memory function than chronological age.
Further research will be needed to assess how epigenetic age relates to longer term changes in cognitive performance, as well as determine which parts of the aging process these chemical markers reflect, the authors wrote in the paper. Going forward, they'd also like to investigate other measures of cognitive ability and types of epigenetic modifications beyond methyl groups.
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