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What’s My Age Again? Our Organs Have Different Biological “Clocks”

What’s My Age Again? Our Organs Have Different Biological “Clocks”

What’s My Age Again? Our Organs Have Different Biological “Clocks”

What’s My Age Again? Our Organs Have Different Biological “Clocks”

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Age, scientists have found, may be more than just a number. Instead, it is at least nine different numbers. Scientists have identified that different organs or body systems age at different rates according to unique biological “clocks”.

Is age only skin deep?

Scientists, alongside septuagenarian ultramarathon runners and anyone following Cher on Twitter, have long suspected that our chronological age is a misleading metric. The idea of calculating “biological age”, a value that would more accurately reflect our health and lifespan, has been around since the 1960s.

But to calculate biological age, biological measurements are needed. Previous studies have flexed the muscles of modern biomedical science to generate estimates based on chemical alterations to our DNA or our bodies’ complement of RNA and proteins. But recent developments in multiomics research, where analyses of different domains of biology are combined for a more in-depth examination, have created space for a far deeper dive into our biological age.

In a new paper published in Cell Reports, researchers based primarily in Shenzhen in south-eastern China have revealed in unprecedented detail the complexity that underlies the aging process.

The team, including senior author Xun Xu of Shenzhen’s Beijing Genomics Institute (BGI) and China National GeneBank (CNGB), recruited over 4,000 volunteers between the (chronological) ages of 20 and 45. These volunteers were poked and prodded extensively, yielding data on 403 different features, including components related to overall fitness, skin features, gut microbiome measurements and 74 different measures of their metabolome.

“Most human aging studies have been conducted on older populations and in cohorts with a high incidence of chronic diseases. Because the aging process in young healthy adults is largely unknown and some studies have suggested that age-related changes could be detected in people as young as their 20s, we decided to focus on this age range,” says co-corresponding author Brian Kennedy of the National University of Singapore.

The team then divided this huge data bank into nine categories and calculated "clocks" for each one:

  • Cardiovascular
  • Renal
  • Liver
  • Sex hormones
  • Facial skin
  • Metabolism/nutrition
  • Immunological
  • Physical fitness
  • Gut microbiome

Some clocks tick in sync

Many features, like body fat, varied extensively by sex, so the data was divided into male and female groups. The researchers then plotted these different biological age measurements against the volunteers' chronological age, revealing that while variation in an individual’s cardiovascular age was largely explainable by the age on their birth certificate, the same could not be said for liver age or renal age, which varied hugely even among people with the same chronological age.

The team then looked at how their different measurements associated with each other, which revealed that while most clocks ticked together, some pairs of clocks were more tightly linked than others. The team even showed a weak negative association between the rate at which the renal system and the microbiota age, something that the researchers suggested may be due to a more diverse microbiome forcing the kidneys to work harder.

The uses of biological age

The team then went on to show the practical use of their multiple clocks. The values could be used to show which component is driving an accelerated aging process in certain individuals – people who are overweight may put extra strain on different body systems, but for some that strain may fall on the liver, whereas it might impact others’ nutrition metabolism systems.

They also reviewed separate data, taken from the United States National Health and Nutrition Examination Survey (NHANES), to determine whether age ratings for the cardiovascular, liver and renal systems could predict mortality. The team showed that a combined rating of all three systems could predict mortality better than any single measurement, such as total cholesterol.

Finally, the team looked at whether biological age measurements could predict longevity, by taking data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) cohort. This dataset featured over 2,000 middle-aged people and another 2,000 centenarians. Could the dataset predict whether an individual was centenarian or not? While the index for skin aging produced, unsurprisingly, very strongly significant results, other metrics, say the authors in the paper, produced no “exceptional predictions.” This is likely due, they write, to the significant impacts of the environment on our bodies, which are harder to predict from purely biological data.

Nonetheless, the results show the unique ways in which time touches each of us and provides what the authors hope could be practical information for future healthcare. “Our study used approaches that can help improve our understanding of aging and – more importantly – could be used some day in real healthcare practice,” says Xu. “We used biomarkers that could be identified from blood and stool samples plus some measurements from a routine body checkup.”

Reference: Nie, C, Li, Y, Li R et al. Distinct biological ages of organs and systems identified from a multi-omics study. Cell Reports. 2022; 38, 110459. doi: 10.1016/j.celrep.2022.110459

Meet the Author
Ruairi J Mackenzie
Ruairi J Mackenzie
Senior Science Writer