"The way we age as we get older is quite distinct from how many times we've traveled around the sun," said Ahmad Hariri, professor of psychology and neuroscience at Duke University.

Now, scientists at Duke, Harvard and the University of Otago in New Zealand have developed a freely available tool that can tell how fast someone is aging, and while they're still reasonably healthy -- by looking at a snapshot of their brain.

From a single MRI brain scan, the tool can estimate your risk in midlife for chronic diseases that typically emerge decades later. That information could help motivate lifestyle and dietary changes that improve health.

In older people, the tool can predict whether someone will develop dementia or other age-related diseases years before symptoms appear, when they might have a better shot at slowing the course of disease.

"What's really cool about this is that we've captured how fast people are aging using data collected in midlife," Hariri said. "And it's helping us predict diagnosis of dementia among people who are much older."

The results were published July 1 in the journal Nature Aging.

Finding ways to slow age-related decline is key to helping people live healthier, longer lives. But first "we need to figure out how we can monitor aging in an accurate way," Hariri said.

Several algorithms have been developed to measure how well a person is aging. But most of these "aging clocks" rely on data collected from people of different ages at a single point in time, rather than following the same individuals as they grow older, Hariri said.

"Things that look like faster aging may simply be because of differences in exposure" to things such as leaded gasoline or cigarette smoke that are specific to their generation, Hariri said.

The challenge, he added, is to come up with a measure of how fast the process is unfolding that isn't confounded by environmental or historical factors unrelated to aging.

To do that, the researchers drew on data gathered from some 1,037 people who have been studied since birth as part of the Dunedin Study, named after the New Zealand city where they were born between 1972 and 1973.

Every few years, Dunedin Study researchers looked for changes in the participants' blood pressure, body mass index, glucose and cholesterol levels, lung and kidney function and other measures -- even gum recession and tooth decay.

They used the overall pattern of change across these health markers over nearly 20 years to generate a score for how fast each person was aging.

The new tool, named DunedinPACNI, was trained to estimate this rate of aging score using only information from a single brain MRI scan that was collected from 860 Dunedin Study participants when they were 45 years old.

Next the researchers used it to analyze brain scans in other datasets from people in the U.K., the U.S., Canada and Latin America.

Faster aging and higher dementia risk

Across data sets, they found that people who were aging faster by this measure performed worse on cognitive tests and showed faster shrinkage in the hippocampus, a brain region crucial for memory.

More soberingly, they were also more likely to experience cognitive decline in later years.

In one analysis, the researchers examined brain scans from 624 individuals ranging in age from 52 to 89 from a North American study of risk for Alzheimer's disease.

Those who the tool deemed to be aging the fastest when they joined the study were 60% more likely to develop dementia in the years that followed. They also started to have memory and thinking problems sooner than those who were aging slower.

When the team first saw the results, "our jaws just dropped to the floor," Hariri said.

Links between body and brain

The researchers also found that people whose DunedinPACNI scores indicated they were aging faster were more likely to suffer declining health overall, not just in their brain function.

People with faster aging scores were more frail and more likely to experience age-related health problems such as heart attacks, lung disease or strokes.

The fastest agers were 18% more likely to be diagnosed with a chronic disease within the next several years compared with people with average aging rates.

Even more alarming, they were also 40% more likely to die within that timeframe than those who were aging more slowly, the researchers found.

"The link between aging of the brain and body are pretty compelling," Hariri said.

The correlations between aging speed and dementia were just as strong in other demographic and socioeconomic groups than the ones the model was trained on, including a sample of people from Latin America, as well as United Kingdom participants who were low-income or non-White.

"It seems to be capturing something that is reflected in all brains," Hariri said.

The work is important because people worldwide are living longer. In the coming decades, the number of people over age 65 is expected to double, reaching nearly one fourth of the world's population by 2050.

"But because we live longer lives, more people are unfortunately going to experience chronic age-related diseases, including dementia," Hariri said.

Dementia's economic burden is already huge. Research suggests that the global cost of Alzheimer's care, for example, will grow from $1.33 trillion in 2020 to $9.12 trillion in 2050 -- comparable or greater than the costs of diseases like lung disease or diabetes that affect more people.

Effective treatments for Alzheimer's have proven elusive. Most approved drugs can help manage symptoms but fail to stop or reverse the disease.

One possible explanation for why drugs haven't worked so far is they were started too late, when the Alzheimer's proteins that build up in and around nerve cells have already done too much damage.

"Drugs can't resurrect a dying brain," Hariri said.

But in the future, the new tool could make it possible to identify people who may be on the way to Alzheimer's sooner, and evaluate interventions to stop it -- before brain damage becomes extensive, and without waiting decades for follow-up.

In addition to predicting our risk of dementia over time, the new clock will also help scientists better understand why people with certain risk factors, such as poor sleep or mental health conditions, age differently, said first author Ethan Whitman, who is working toward a Ph.D. in clinical psychology with Hariri and study co-authors Terrie Moffitt and Avshalom Caspi, also professors of psychology and neuroscience at Duke.

More research is needed to advance DunedinPACNI from a research tool to something that has practical applications in healthcare, Whitman added.

But in the meantime, the team hopes the tool will help researchers with access to brain MRI data measure aging rates in ways that aging clocks based on other biomarkers, such as blood tests, can't.

"We really think of it as hopefully being a key new tool in forecasting and predicting risk for diseases, especially Alzheimer's and related dementias, and also perhaps gaining a better foothold on progression of disease," Hariri said.

The authors have filed a patent application for the work. This research was supported by the U.S. National Institute on Aging (R01AG049789, R01AG032282, R01AG073207), the UK Medical Research Council (MR/X021149/1), and the New Zealand Health Research Council (Program Grant 16-604).

PFAS have been linked with a range of health issues including decreased fertility, developmental delays in children, and a higher risk of certain cancers and cardiovascular diseases.

Scientists at the University of Cambridge have identified a family of bacterial species, found naturally in the human gut, that absorb various PFAS molecules from their surroundings. When nine of these bacterial species were introduced into the guts of mice to 'humanise' the mouse microbiome, the bacteria rapidly accumulated PFAS eaten by the mice -- which were then excreted in faeces.

The researchers also found that as the mice were exposed to increasing levels of PFAS, the microbes worked harder, consistently removing the same percentage of the toxic chemicals. Within minutes of exposure, the bacterial species tested soaked up between 25% and 74% of the PFAS.

The results are the first evidence that our gut microbiome could play a helpful role in removing toxic PFAS chemicals from our body -- although this has not yet been directly tested in humans.

The researchers plan to use their discovery to create probiotic dietary supplements that boost the levels of these helpful microbes in our gut, to protect against the toxic effects of PFAS.

The results are published today in the journal Nature Microbiology.

PFAS (Perfluoroalkyl and Polyfluoroalkyl Substances) can't be avoided in our modern world. These man-made chemicals are in many everyday items including waterproof clothing, non-stick pans, lipsticks and food packaging, used for their resistance to heat, water, oil and grease. But because they take thousands of years to break down, they are accumulating in large quantities in the environment - and in our bodies.

Dr Kiran Patil, in the University of Cambridge's MRC Toxicology Unit and senior author of the report, said: "Given the scale of the problem of PFAS 'forever chemicals', particularly their effects on human health, it's concerning that so little is being done about removing these from our bodies."

"We found that certain species of human gut bacteria have a remarkably high capacity to soak up PFAS from their environment at a range of concentrations, and store these in clumps inside their cells. Due to aggregation of PFAS in these clumps, the bacteria themselves seem protected from the toxic effects."

Dr Indra Roux, a researcher at the University of Cambridge's MRC Toxicology Unit and a co-author of the study said: "The reality is that PFAS are already in the environment and in our bodies, and we need to try and mitigate their impact on our health now. We haven't found a way to destroy PFAS, but our findings open the possibility of developing ways to get them out of our bodies where they do the most harm."

There is increasing concern about the environmental and health impacts of PFAS, and in April 2025 the UK launched a parliamentary inquiry into their risks and regulation.

There are over 4,700 PFAS chemicals in widespread use. Some get cleared out of the body in our urine in a matter of days, but others with a longer molecular structure can hang around in the body for years.

Dr Anna Lindell, a researcher at the University of Cambridge's MRC Toxicology Unit and first author of the study said: "We're all being exposed to PFAS through our water and food - these chemicals are so widespread that they're in all of us.

"PFAS were once considered safe, but it's now clear that they're not. It's taken a long time for PFAS to become noticed because at low levels they're not acutely toxic. But they're like a slow poison."

Lindell and Patil have co-founded a startup, Cambiotics, with serial entrepreneur Peter Holme Jensen to develop probiotics that remove PFAS from the body, and they are investigating various ways of turbo-charging the microbes' performance. Cambiotics is supported by Cambridge Enterprise, the innovation arm of the University of Cambridge, which helps researchers translate their work into globally-leading economic and social impact.

While we wait for new probiotics to become available, the researchers say the best things we can do to help protect ourselves against PFAS are to avoid PFAS-coated cooking pans, and use a good water filter.