By Dr Saima Ajaz, Medical Lead, Harley Longevity Club
Feeling well is not the same as being healthy.
One of the biggest misconceptions is that if something is wrong inside the body, we will know about it. Unfortunately, many conditions and risk factors that affect long-term health can develop silently, without pain, obvious symptoms, or any dramatic warning.
High blood pressure and high cholesterol are classic examples. You can feel completely well while these risk factors quietly increase your risk of cardiovascular disease.
Metabolic changes can develop gradually. Blood sugar regulation can become less efficient. Blood pressure can creep upwards. Visceral fat can accumulate around the organs. Muscle mass and physical capacity can begin to decline.
For a considerable period, you may not feel any different.
Disease becomes clinically apparent at a certain point, but physiological changes may occur long before that.
That is where modern preventive medicine has enormous potential.
The goal of preventive medicine is not to convince healthy people that they are ill or to scare them. It is to identify the changes we can act on today, before they become the diseases we have to treat tomorrow.
The Liver
Liver disease is mostly silent and 90% can be prevented.
As a doctor specialising in liver and metabolic health, one of the clearest examples of the importance of prevention is metabolic dysfunction-associated steatotic liver disease, or MASLD, previously commonly called non-alcoholic fatty liver disease.
In its October 2025 update, the British Liver Trust described MASLD as a “silent epidemic” and reported that up to 1 in 5 people may have MASLD; as many as 12% of those may have the more serious inflammatory form, metabolic dysfunction-associated steatohepatitis (MASH) – a more advanced form of MASLD where the excess fat is accompanied by inflammation and liver cell injury, which can lead to fibrosis (scarring), cirrhosis and, in some cases, liver cancer.
The challenge is that liver disease can develop without obvious symptoms. By the time someone becomes aware that something is wrong, significant changes may already have taken place.
MASLD is particularly important because it is not simply a condition of the liver. Fat accumulation in the liver can be a marker of wider metabolic dysfunction and is associated with conditions such as obesity, type 2 diabetes, abnormal blood lipids and cardiovascular disease.
Advances in testing are now helping us identify people at greater risk earlier and distinguish those who are more likely to develop serious liver damage. At the same time, new treatments are being developed to address both the underlying metabolic problems and liver disease itself. This represents an important shift towards identifying risk sooner and intervening before significant damage occurs.
It also challenges another common assumption: that you can tell how healthy someone is simply by looking at them.
Body weight and BMI can be useful measures, but they do not tell us everything about body composition or where fat is being stored. Visceral fat is metabolically different from fat stored elsewhere.
Someone can therefore look relatively slim and still have metabolic risk.
This is why prevention matters. Identifying metabolic changes earlier allows us to address underlying risk factors before they progress to more serious disease.
The Numbers Game
We have become accustomed to thinking in terms of individual numbers.
“My cholesterol is normal.”
“My blood sugar is fine.”
“My blood pressure isn’t high.”
“My weight hasn’t changed.”
These are all useful pieces of information, but health is more complicated than any single measurement.
What interests me clinically is the pattern.
How are your glucose and lipid markers behaving together? What is happening to your blood pressure? How much muscle do you have? Where is your body storing fat? How fit are you? Are there changes over time?
A single snapshot can be reassuring, but a series of measurements can tell us much more about the direction of travel.
This is why I believe the future of preventive healthcare is increasingly about creating a health dashboard, rather than chasing one perfect number.
The value is not simply in collecting more data. It is in putting the right information together, understanding what it means and, importantly, knowing what to do with it.
Fitness
Another area we sometimes overlook is physical fitness.
We tend to think of fitness as something relevant to athletes or people who want to improve their performance. But cardiorespiratory fitness is also an important marker of health.
Measures such as VO₂ max give us an indication of how effectively the body can use oxygen during exercise and provide information about cardiovascular and physical capacity.
Similarly, strength matters.
Research involving millions of participants has found associations between lower handgrip strength and higher risks of mortality and disability, although, these are associations rather than proof that grip strength itself causes longer or shorter life.
Why does this matter?
Because health isn’t simply about what our blood tests say. It is also about what our bodies are capable of doing.
Can we climb stairs without becoming breathless? Can we lift and carry things? Can we maintain muscle as we age? Can we recover from physical exertion?
These are measures of functional reserve — our capacity to cope with the physical demands of life.
And preserving that reserve becomes increasingly important as we get older.
Physiological Reserve
This is the question I would like more people to ask.
Two people can be exactly the same chronological age and have very different levels of cardiovascular fitness, muscle mass, visceral fat, metabolic health and organ function.
Chronological age tells us how many years we have lived. It doesn’t tell us how well our biology is coping with those years.
This is where the emerging science of biological ageing is fascinating. Researchers are exploring biomarkers that may provide information about biological ageing and how our bodies are changing over time.
But we should be careful not to turn biological-age testing into a crystal ball.
No single epigenetic or biological-age test can tell you exactly how long you will live, nor should it be treated as a definitive diagnosis of your health. These are rapidly developing areas of science, and their clinical applications continue to evolve.
What they can potentially offer is another piece of information — one that, when interpreted alongside established clinical measures, may help us understand the bigger picture.
Chronological age is fixed, whereas biological health is heterogeneous and should be understood through multiple dimensions and over time.
That is why I believe biological-age measures are best considered as part of a broader health assessment, rather than as a standalone verdict on how well or how long someone will live.
From Treating Disease to Protecting Health
This represents an important shift in medicine.
Traditional healthcare has necessarily focused on diagnosing and treating disease. That remains essential.
But we now have an opportunity to complement this with a more proactive approach: identifying risk before it becomes disease and maintaining physical and metabolic function for as long as possible.
This is the philosophy behind the increasingly sophisticated approach to longevity medicine, including the work we undertake at the Harley Longevity Club.
The aim isn’t simply to ask, “Are you ill?”
It is to build a more complete picture of an individual’s health, bringing together appropriate biomarkers, body composition, cardiovascular and physical fitness, strength and other relevant measures, and then using that information to identify where intervention may be beneficial.
Feeling Well Should Be the Beginning, Not the End
I don’t want people to become anxious about their health.
I want people to feel empowered by understanding it.
Feeling well is wonderful. But it shouldn’t necessarily be the end of the conversation.
You can feel energetic and still have high blood pressure. You can exercise regularly and still have metabolic risk. You can look slim and still carry excess visceral fat. You can have no symptoms and still have early changes taking place inside your body.
The answer is not to test everything or become obsessed with numbers.
It is to understand that prevention allows us to act earlier.
The more we understand about our health, the more opportunity we may have to protect it.
For me, that is the real promise of preventive and longevity medicine: not simply adding years to life, but helping people preserve their health, function and independence for as long as possible.
