If you’ve never heard of intrinsic capacity, you’re not alone, but it’s becoming the preferred way to measure and assess human ageing, reports The New York Times.
Its goal is a single metric that could capture every aspect of your health – how strong you are, how clear your vision is, how sharply you think –a holistic measure of what someone’s body and mind are capable of.
“It’s not really a sexy term, but it makes sense from a scientific perspective,” said Dr John Beard, a professor of productive ageing at the Columbia University Mailman School of Public Health who helped to develop the concept.
“‘Intrinsic’ means all of those attributes that you can attribute to the individual from the skin in,” he said. “And ‘capacity’ is looking at their functioning.”
You can’t ask your doctor to test your intrinsic capacity just yet, but experts hope that physicians will eventually use it with older patients to track their health and well-being, and potentially with younger patients, too.
More immediately, longevity scientists think it may be the key to demonstrating whether a medication or lifestyle change aimed at slowing ageing actually works.
How does the metric work?
Intrinsic capacity was formally defined in 2015 by the World Health Organisation as part of its healthy ageing initiative, which in part aims to move doctors and scientists away from focusing on disease and toward maximising and maintaining older adults’ functional abilities.
Experts derive someone’s intrinsic capacity score from their performance on five “subdomains”: cognition, locomotion (strength and mobility), sensory capacity (vision and hearing), psychological well-being and vitality (overall energy levels and resilience to physical stressors).
Many of the tests that assess these subdomains are already used to evaluate older adults’ health, such as grip strength and walking speed.
Researchers have shown that intrinsic capacity correlates with older adults’ risk of disability and mortality. But experts say the real clinical value will come from following a person’s intrinsic capacity over time.
That could enable doctors to identify any signs of decline early on and take steps to stop or slow the trajectory.
“Even when people are quite robust and they don’t have any diseases, we can still detect changes in capacity,” Beard said. “And that allows you to start thinking about, well, OK, what’s making people’s capacity different, and how can we intervene much earlier to try to prevent the later life declines?”
For now, many of the tests that assess elements of intrinsic capacity, like those to detect cognitive impairment, are useful only in older adults, since almost all younger, healthier people get a perfect or near-perfect score. But scientists are exploring whether other measures with more variability at every age could be used to assess intrinsic capacity in younger people, too.
How is the metric currently being used?
Intrinsic capacity is being studied in clinical trials, including a real-world experiment under way in France. In the study, older adults regularly fill out a questionnaire to assess their intrinsic capacity and receive personalised recommendations based on their score.
If a person’s score starts to decline, they are quickly referred to their doctor or a trained geriatric nurse for follow-up testing and treatment.
The research is still preliminary and scientists don’t yet know whether intervening early, informed by the intrinsic capacity score, will help someone to live longer.
“We expect it will,” said David Furman, a professor at the Buck Institute for Research on Ageing who has collaborated with the researchers leading the study, “but we don’t have the data yet.” (A similar study of intrinsic capacity, the first in the United States, has just begun in New Mexico.)
Intrinsic capacity is also the focus of a new research programme funded by ARPA-H (the Advanced Research Projects Agency for Health), part of the US Department of Health and Human Services. The programme’s ultimate goal is to pave the way for drugs that extend health span to be approved by the FDA.
There aren’t yet any approved longevity drugs for a couple of reasons. For one, it’s very difficult for researchers to determine whether a drug increases lifespan because that would require a clinical trial running for several decades, which is prohibitively expensive.
Scientists have been looking for proxies of ageing they can use instead, and they think intrinsic capacity might be the one.
Another hurdle is that the FDA doesn’t consider ageing to be a disease, so it doesn’t evaluate drugs for their ability to alter the ageing process.
Andrew Brack, who is leading the ARPA-H programme, thinks intrinsic capacity could be a way around this. This idea isn’t unprecedented: after a long debate over whether to designate old age as a disease, in 2022 the WHO instead added “ageing associated decline in intrinsic capacity” to the 11th edition of the International Classification of Diseases list. (Most countries, including the United States, still use the older ICD-10.)
Through the ARPA-H project, scientists are trying to demonstrate two main things: first, that someone’s intrinsic capacity corresponds to how they feel or function, or how long they live; and second, that it’s possible to improve a person’s intrinsic capacity with lifestyle interventions like exercise, or with existing drugs that have been proposed to have a longevity benefit, like GLP-1s.
If successful, intrinsic capacity could become a metric used to evaluate drugs that target ageing, which could ultimately open the door for the first FDA-approved longevity medication.
“We have to be clear, we don’t know if this will work,” Brack said. But, he added, “we’re scientists; we have to do the experiment”.
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