(September 2025) People age at very different rates. Some stay sharp, active and healthy well into their later years, while others face health problems much earlier.

Even though research on ageing has come a long way, there are still big gaps. Many studies have focused on “biological clocks” in the body or brain, which try to represent how quickly people are ageing inside. But few have looked at what the researchers here call a biobehavioural clock – a measure that combines both health and lifestyle factors.

One area that has been especially overlooked is the political dimension. The state of democracy and strength of institutions are increasingly recognised as critical determinants of health, yet their role in ageing has hardly been explored.

Dr Hernan Hernandez, Dr Hernando Santamaria-Garcia and Dr Agustin Ibanez of the Latin American Brain Health Institute in Chile, together with colleagues from the Global Brain Health Institute at Trinity College Dublin, analysed data from over 160,000 adults aged 51 to 90 across Latin America, Europe, Asia, and Egypt. Their goal was to estimate each participant’s “biobehavioural age” (how old their body and mind seemed) based on health and lifestyle, rather than just counting birthdays. Calculating the gap between biobehavioural age and chronological age allowed them to see which populations were ageing faster or slower, and what country-level conditions might explain the differences.

What actually makes us age?

Ageing can speed up or slow down depending on a mix of personal and external factors. At the individual level, things like education, cardiometabolic conditions, disabilities, smoking, lack of exercise and heavy drinking all play an important role.

Country-level conditions can also strongly shape ageing. These include the physical environment (e.g. pollution), the social environment (e.g. structural inequalities), and even the political environment (such as political instability and weakening democracy). The study refers to all these factors as part of the “exposome” - everything an individual is exposed to over a lifetime.

A huge sample size from 40 countries across 4 continents

Published in Nature Medicine, the study drew on data from 40 countries (7 in Latin America, 27 in Europe, 4 in Asia and 2 in Africa). To do this they compared European data from SHARE with that of its sister studies around the world. All participants were part of large, nationally representative health and ageing surveys collected through face-to-face interviews using strict sampling methods.

Two ways of looking at ageing

The study had two main parts:

• A snapshot study (cross-sectional) to compare ageing across countries at one point in time.
• A follow-up study (longitudinal) tracking people over several years to see what predicts healthier aging.

Turning health and environmental data into an ageing score

The researchers scoured previous research to identify factors linked to accelerating and decelerating ageing, and that could be compared across countries. The study didn’t just look at individual health habits—it also examined the exposome, such as income inequality, gender equality, political freedoms, and air quality.

They used machine learning – a type of artificial intelligence – to predict each person’s age based on these health and lifestyle factors. Comparing this to their real age gave a biobehavioural age gap:

• If predicted age was higher, it meant accelerated ageing.
• If it was lower, it meant slower ageing.

Table: Individual-level factors in ageing

Where you live affects how quickly you age

Results showed big differences between regions. Europeans generally aged more healthily, while participants in Egypt and South Africa aged faster. Latin America and Asia fell in between. Even within Europe, eastern and southern countries showed more accelerated ageing than western ones.

Across the globe, lower income was strongly linked to faster ageing. Countries with higher inequality, more political restrictions and poorer air quality aged considerably faster – even after running extra tests to make sure outliers or overlapping factors weren’t skewing the results.

Education was one of the top factors that protected against faster ageing.

The link between political instability and ageing

Political conditions shape everything from healthcare access and social safety nets to stress levels. For example, political polarisation and lack of trust in government can make people less likely to seek healthcare and follow public health advice.

Institutional instability, like sudden policy changes or underfunded health systems, create uncertainty and deepen health inequalities.

Chronic exposure to this instability can also create chronic strain in an individual, damaging the heart, brain and other systems, speeding up ageing.

The researchers stress that this isn’t about blaming countries but about highlighting structural vulnerabilities to support policies that protect people’s health everywhere.

Your biobehavioural age today predicts health four years later

For people followed over time, the study asked: does your biobehavioural age today predict your health years later? The answer was yes. People with slower ageing scores tended to keep their memory, independence, and well-being for longer. Those ageing faster were more likely to decline over the four years they were followed.

Learning from people who defy their years

Ageing is not set in stone. It’s shaped by health habits, education and social conditions – all of which are changeable. By spotting who is ageing faster, we can intervene earlier, not just to extend life, but to extend healthy life.

Intriguingly, the model estimated some participants to be biologically younger than their chronological age. Looking at the things these individuals have in common could reveal new ways to help others avoid premature ageing.

Study by Hernandez, H., Santamaria-Garcia, H., Moguilner, S. et al. The exposome of healthy and accelerated aging across 40 countries. Nat Med (2025).

URL: https://doi.org/10.1038/s41591-025-03808-2

Picture: © Adobe Stock / Jesse B/peopleimages.com