Researchers have found that a person's biological age is separate and distinct to his or her chronological age.
The findings, published in Genome Biology, could help improve management of age-related disease by identifying people most at risk of diseases affected by age, as well as improve the way anti-ageing treatments are evaluated.
The seven-year collaborative study at King's College London, Karolinska Institutet in Sweden and Duke University in the USA, used a process called RNA-profiling to measure and compare gene expression in thousands of human tissue samples.
Rather than looking for genes associated with disease or extreme longevity, the UK Medical Research Council (MRC)-funded researchers discovered that the 'activation' of 150 genes in the blood, brain and muscle tissue were a hallmark of good health at 65 years of age.
The researchers were then able to create a reproducible formula for 'healthy ageing', and use this to tell how well a person is ageing when compared to others born the same year.
The researchers found an extensive range in 'biological age' scores of people born at the same time indicating that a person's biological age is separate and distinct to his or her chronological age.
Importantly, a low score was found to correlate with cognitive decline, implying that the molecular test could translate into a simple blood test to predict those most at risk of Alzheimer's disease or other dementias and suitable for taking part in prevention trials.
A person's score was not, however, found to correlate with common lifestyle-associated conditions, such as heart disease and diabetes, and is therefore likely to represent a unique rate of ageing largely independent of a person's lifestyle choices.
The researchers say their findings provide the first practical and accurate test for the rate at which individual bodies are ageing. If this is the case, it could lead to numerous insights in research because 'age' is a critical factor in almost every area of medicine.
At the same time, the molecular test could enable more suitable donor matching for older organ transplants and could also provide a more efficient way of determining if an animal model of ageing is suitable to evaluate the effectiveness of anti-ageing treatments.
However, the study does not provide insight into how to improve a person's score and thus alter their 'biological age'.
While a low score could be considered as 'accelerated ageing', an important aspect of the work suggests that ageing does not now need to be defined only by the appearance of disease.
Lead author of the study, Professor James Timmons at the Division of Genetics and Molecular Medicine at King's College London, says, "Given the biological complexity of the ageing process, until now there has been no reliable way to measure how well a person is ageing compared with their peers. Physical capacity such as strength or onset of disease is often used to assess 'healthy ageing' in the elderly but in contrast, we can now measure ageing before symptoms of decline or illness occur.
"We now need to find out more about why these vast differences in ageing occur, with the hope that the test could be used to reduce the risk of developing diseases associated with age."
Dr Neha Issar-Brown, programme manager for population health sciences at the MRC adds, "Whilst it is natural for our bodies and brains to slow down as we age, premature ageing and the more severe loss of physical and cognitive function can have devastating consequences for the individual and their families, as well as impact more widely upon society and the economy.
'This new test holds great potential as with further research, it may help improve the development and evaluation of treatments that prolong good health in older age.'
This research was funded by the Medical Research Council, the Innovative Medicines Initiative (EU/EFPIA), the Wallenberg Foundation and the National Institutes of Health.