A new study sheds light on why some people stay healthy and sharp into old age while others experience decline much earlier. Researchers from Duke University, Harvard, and the University of Otago in New Zealand have created a program that uses a single brain MRI to forecast how quickly a person ages. This study, published on July 1 in Nature Ageing, could someday assist in identifying people who are at risk for chronic diseases, like dementia, years before symptoms arise. 

"The way we age as we get older is quite distinct from how many times we've travelled around the sun," said Ahmad Hariri, a neurologist at Duke. In other words, biological age (the wear and tear on the body and brain) does not always correspond to the number of years lived. 

The new technology, DunedinPACE Neuroimaging (DunedinPACNI), measures the rate of ageing by analysing brain scan patterns. This measure differs from the typical concept of "ageing clocks", which frequently employ a single blood test or compare multiple age groups at the same point. 

Hariri and his team intended to avoid outcomes that were skewed by generational differences, such as exposure to leaded petrol or smoking prevalence. To do so, scientists examined data from New Zealand's long-running Dunedin Study, which has monitored over 1,000 people born in the early 1970s. They created an indicator of how quickly these volunteers were ageing by tracking changes in health markers such as blood pressure, body weight, and kidney function over decades. 

They then trained the novel brain-scan-based technology on MRI scans of these people aged 45. When tested on various groups from the United States, the United Kingdom, Canada, and Latin America, the tool consistently identified people who aged faster. 

People with faster ageing scores fared poorly on memory and cognitive tests. They demonstrated quicker shrinkage in the hippocampus, a region of the brain responsible for memory. 

In one North American dataset of persons aged 52 to 89, those who aged the fastest were 60% more likely to get dementia. They also had memory issues sooner. 

Beyond brain health, quicker-ageing individuals were 18% more likely to be diagnosed with a chronic condition, such as heart disease or stroke, in the coming years. Alarmingly, they were 40% more likely to die during that time than individuals who aged more slowly. 

The number of individuals over 65 is expected to increase by 2050, accounting for about a quarter of the global population (United Nations, 2022). Dementia cases are increasing in tandem. The World Health Organisation predicts that over 55 million individuals suffer from dementia now, with the figure likely to nearly quadruple by 2050. 

The economic burden is huge. According to a 2020 article in the Alzheimer's & Dementia journal, the global cost of Alzheimer's care will increase from $1.33 trillion in 2020 to more than $9 trillion by 2050. 

Despite extensive research, medicines have yet to halt or reverse Alzheimer's. Hariri suggests that one cause could be that medications are administered too late, when significant brain damage has happened. 

The researchers believe that their technology will be able to identify at-risk individuals earlier, allowing them to intervene before major damage occurs. However, it is not yet suitable for ordinary medical use. More research is needed to establish its efficacy and determine how it may be integrated into healthcare. 

Ethan Whitman, research co-author, stated, "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."