Katy Perry took to Instagram this week to proudly share that her "biological age" is 33 – that's eight years younger than her actual age, 41.
The Firework singer, who is dating Justin Trudeau (whose biological age is 43, actual age 54, if you wondered), found out her biological age via Function Health, a service that reveals how old you are on the inside via 160 lab tests performed on a blood sample.
© InstagramI had my biological age tested last year, and I'm happy to report my results said I was 31, five years younger than my actual age, 36. Not quite at Katy's level, but not to be sniffed at!
What is biological age?
For the uninitiated, biological age refers to how well your body functions at a cellular and physiological level, rather than the number of years you’ve been alive – also known as your chronological age.
Unlike our actual age, biological age is reversible and something you can work on to improve.
Katy isn't the only celeb who has found out their biological age. Khloe Kardashian tested hers, finding out she was just 28 when she was 40, compared to Kim Kardashian, who was deemed to be 34 when she was 43.
© GettyWhy do we need to know our biological age?
While it can seem like a vanity project - or simply something to boast about if you're a Kardashian - there are serious benefits to knowing our biological age, says longevity expert Dr. Mohammed Enayat.
Biological age can be a great indicator of the impact your lifestyle, environment, genetics, and behaviours have had on key systems in the body, including metabolic health, inflammation, hormonal balance and cellular repair.
© Getty ImagesHe adds that understanding our biological age gives a clear, actionable picture of our health, allowing us to identify any problems and take action. For example, my test revealed my cholesterol was on the higher side of normal, so I adjusted my diet to try to get my age down (I haven't had my follow-up test yet, so can't say if it worked).
Knowing your biological age also provides a measurable benchmark, so you can track whether the changes you're making are improving your health at a cellular level.
How is our biological age tested?
Biological age is normally determined via blood tests. Dr. Enayat's London clinic, Hum2n, tests biological age through a combination of blood biomarker analysis paired with functional health data.
"This typically involves a comprehensive blood panel looking at markers linked to longevity, including inflammation (such as CRP), metabolic health (glucose regulation, insulin sensitivity), lipid profiles, liver function, micronutrient status, and hormonal balance," he says.
"The goal is to build a detailed picture of how your body is functioning beneath the surface, not just identifying disease, but detecting early imbalances that influence the biological ageing process," Dr. Enayat says.
How quickly can we turn our biological age around?
I was lucky that my biological age was lower than my actual age, but what can we do if it's older? Or if we simply want to improve it?
"The really encouraging thing is that biological age is modifiable and can be altered relatively quickly, with the right interventions," says Dr. Enayat. "In many cases, we can see measurable improvements within eight to 12 weeks."
He cautions that sustained reductions in biological age typically occur over several months, depending on the individual and the starting point. "Longevity is not about quick fixes; it’s about consistent improvements," he adds.
How I got my low biological age
There are several factors I attribute my low biological age to, and while I can't speak for Khloe, Kim and Katy, I'd say many of them apply to them, too.
1. Exercise
Dr. Enayat told me that muscle mass is one of the strongest predictors of longevity, and I am committed to strength training, normally doing two sessions per week.
"Resistance training improves insulin sensitivity, supports metabolic health, and reduces mortality risk," Dr. Enayat says of why it contributes to a younger biological age. "Alongside this, improving cardiovascular fitness is critical; even small increases are associated with longevity benefits."
© Getty ImagesI've got this box ticked, too. I ran a half-marathon last year, following a training plan on Runna, plus I spin at least once a week.
2. Sleep and recovery
Sleep is the area of longevity I excel in. My average Oura sleep score is around 92, and I get on average 7 hours and 52 minutes of sleep per night.
I'm always in bed before 10:30, I don't drink coffee after midday (except on special occasions…), and I'm active during the day, to make sure I'm sleepy at bedtime."
© Getty Images"Sleep is where repair happens," Dr. Enayat says of how sleep keeps us young. "Poor sleep accelerates biological ageing by increasing inflammation, impairing glucose metabolism, and disrupting hormonal balance. Deep, consistent sleep supports cellular repair, cognitive function, and longevity pathways. This includes not just duration, but quality."
3. Stress and nervous system regulation
I track my stress on my Oura ring, and I tend to be in the "thriving" category of stress management. I think this is down to the two points above – sleeping well and exercising a lot. I also make plenty of time for things I enjoy, such as spending time outside and seeing friends – it's simple, but it works!
On why stress ages us, Dr. Enayat says: "Chronic stress is one of the most underestimated drivers of accelerated biological ageing. Elevated cortisol over time impacts everything from immune function to fat distribution and cognitive health. Practices that regulate the nervous system, i.e. breathwork, mindfulness, or structured downtime, are critical for long-term health."
Areas I need to work on
I'd love to say I'm perfect in my health and wellness routine, but there are areas that I could work on to become as young as Khloe.
1. Nutrition and metabolic health
"Blood sugar control is important for ageing well," confirms Dr. Enayat. "Diets that minimise glucose spikes and support metabolic flexibility are important, as is prioritising whole foods, protein, healthy fats and fibre. Overconsumption of ultra-processed foods and sugars accelerates inflammation and cellular damage which contribute to ageing."
2. Micronutrients and targeted supplementation
Deficiencies in key nutrients, such as vitamin D, magnesium, omega-3 fatty acids, and B vitamins can accelerate ageing processes. While I take vitamin C and collagen, I'm not dedicated to my supplement routine at present – and getting on top of this could help with my biological age.
"Targeted supplementation, based on testing rather than guesswork, can support mitochondrial function, reduce inflammation, and optimise energy production. This is where a personalised approach is essential," says Dr. Enayat.
