Measuring longevity: Making the case for functional age

Zest CEO on why functional age may provide a better measure for consumer longevity interventions than biological age.

The concept of biological age is a hot topic in longevity these days. In principle, the idea makes perfect sense – a better, more scientific way to quantify the extent to which someone has aged, rather than the number of years they have been alive (their chronological age).

Measuring biological age has become a useful tool in the field of aging and longevity research, where scientists seek to assess the effectiveness of potential lifespan-extending interventions. But today, the idea of biological age is increasingly being marketed to consumers, with a host of tests available to those interested in knowing if their longevity regimens are having any effect.

Longevity.Technology: There are many different approaches to measuring biological age, from epigenetic patterns and microbiome data to blood-based biomarkers, but could there be a better way to measure changes to our healthspan? Rather than focus on biological age, consumer longevity startup Zest is preparing to launch a new AI-powered platform that is focused on measuring changes to what it calls “functional age” in order to evaluate your progress. Ahead of the company’s launch, we caught up with Zest founder and CEO Dr Julia Cooney to learn more about functional age and how it differs from biological age. 

A Cambridge-educated medical doctor and scientist, Cooney was inspired to start Zest when she noticed the trend towards biological age calculations being used more as a consumer tool than a scientific research tool.

Measuring longevity: Making the case for functional age
Dr Julia Cooney (left) with Zest colleagues

“Things like epigenetic clocks, for example, were started to fulfil a clear need, which is to have some kind of proxy measure for age that we can use in longevity research,” she says. “Because we obviously can’t run a trial for 50 years to see how an intervention affects lifespan, we need to have a proxy measure for age. And that led to DNA methylation and biological clocks, which is all well and good, but in recent years, they’re being used more and more in the consumer space.”

Growing consumer interest in biological age

First and foremost, says Cooney, the fact that the general population is becoming interested in something like biological age is clearly a good thing.

“I think people taking an interest in their health and in their longevity is actually fantastic, but I don’t think that these tools were designed for that purpose. And I don’t think they’re very well suited for that purpose.”

Expanding further, Cooney uses the increasing popularity of DNA methylation clocks as an example. 

“It actually takes quite a long time for changes that you implement in your lifestyle to be reflected in those biological clocks,” she says. “Research suggests that you can start implementing a daily exercise protocol, for example, and it can take up to two years to see any kind of changes in your epigenetic clock.”

This, says Cooney, can be demotivating for people seeking signs that their actions to improve healthspan and longevity are having an effect.

“Let’s say somebody does a DNA methylation test, which tells them they’re not doing so well, so they commit to a whole year of eating well and exercising,” she explains. “As a result, they feel they are sleeping better, their moods better, they’re lifting heavier in the gym, they’re running further – they’re feeling great! And then they redo the test, and nothing’s changed. That’s pretty demoralising – they are feeling better than they were a year ago, and the test isn’t showing that.”

Reflecting lived experience is key

Another issue that Cooney has with biological age clocks is that there isn’t enough research that correlates biological age with a person’s lived experience.

“We know that these epigenetic clocks are highly accurate at correlating to chronological age, but they’re not good at reflecting functional abilities, particularly in younger people,” she says. “There have been many studies showing that a lower epigenetic age is not linked to any improvements in functional measures such as cardiorespiratory fitness, walking speed and muscle strength. So your epigenetic age doesn’t capture how young you actually feel, and may not reflect your body’s physical and cognitive abilities.”

“There’s a lot of data that suggests that people who feel younger, live longer, and we felt it was important to reflect this correlation in a calculation. That’s the gap we identified in the current biological clock landscape.”

Introducing functional age

To address this gap, Zest set about developing a calculation that would change as new interventions are implemented – a calculation that Cooney calls functional age.

“As you reduce your functional age, as you improve your physical functionality, we want a clock that could reflect that,” says Cooney. “And we also wanted a clock that reflects your lived experience, so that people who are bounding out of bed in the morning and feeling great can then look at their clock and see something that actually reflects how they feel.”

The concept of functional age is already well-understood in the aged care field, but Zest is aiming to make it relevant for a much younger demographic.

“I’ve worked in aged care and a lot of the measures are super interesting, but they’re just not relevant for younger population,” says Cooney. “We’ve got a lot of government funded research into measuring frailty, but measuring physical functionality in the younger population isn’t something that’s ever needed to be investigated or funded as part of a research project.”

Zest’s calculation aims to allow people of all ages and abilities to assess their functional capabilities and track any changes within it.

“It’s a huge gap that we’re trying to fill – partly extrapolating from what has been done very successfully in elderly people,” says Cooney. “But we’ve also had to devise new tests that are more applicable to a younger population.”

Measuring longevity: Making the case for functional age

Tracking multiple longevity biomarkers

At the core of Zest’s algorithm lie digital, functional and blood biomarkers that Cooney says are “practical, holistic, functional and reflective of lived experience.”

“The blood biomarkers that we’ve selected are ones that have been shown time and time again to be very well correlated to healthspan and lifespan,” she says. These include well-established blood panel markers like HDL, LDL, albumin, CRP for inflammation, glucose and HbA1c for glucose metabolism, and hormones like estrogen, testosterone, SHBG, and DHEAS.

The digital biomarkers collected as part of Zest’s functional age calculation include things like VO2max, heart rate variability and sleep quality.

“We know something like VO2 max is well correlated to healthspan and lifespan, and also gives insight into things like your lung and cardiovascular function,” says Cooney.

The third and final pillar of Zest’s approach is about measuring functional biomarkers, which includes cognitive testing, mood assessments, and grip strength.

Zest’s AI algorithm then compares all the measurements to age-matched reference values and factors in your chronological age to give an estimate of functional age, which, says Cooney, “is reflective of your physical and cognitive performance in your day-to-day life.”

“This means that as you begin to optimize your lifestyle and feel healthier and stronger, the improvement will be reflected in your functional age. We believe this positive feedback for lifestyle interventions will help people stay motivated and track progress on a shorter-term basis, improving adherence to longevity routines.”

Zest is currently in beta testing and will be launching its app later this summer – watch this space!

Photograph: kjpargeter/Freepik