I’M WELL, thank you. Or at least I think I am. I have no major illness to speak of, I am of average weight and a recent knee scan showed my joints are sufficiently well oiled. My blood pressure is spot on and I exercise fairly regularly – at least, some of the time. Then again, I have a cough I can’t shake. I don’t feel physically strong. And since I am turning 40, I should really get a mammogram, given my family history of breast cancer.
So, am I healthy? With my “big birthday” looming, I have increasingly found myself wondering about that – about what it is to be healthy and how we can best measure whether we are or not. I had assumed there would be some well-established way to find out. But when I began to investigate, I soon discovered that it is a surprisingly hard question to answer.
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That is partly because we now know that many of the metrics we rely on, such as body mass index (BMI), are flawed. But it is also the result of fresh insights into the microbiome and the immune system, among other things. These are giving rise to a whole new raft of tests promising a better gauge of health – from those that probe your gut bacteria or your metabolites to those that provide you with an “immune grade”. So, which of these new tests, if any, should I be turning to for the ultimate health check?
What does it mean to be healthy?
Your common-sense definition of what it means to be healthy probably roughly aligns with what the dictionary says – namely, that health is “the condition of the body and the degree to which it is free from illness”, to borrow from the Cambridge Dictionary.
The World Health Organization (WHO) is a little stricter. It defines health as . Although this definition was adopted by 61 countries in 1946, it has since been criticised. The requirement for “complete” well-being means most of us would qualify as unhealthy most of the time. Another obvious problem is that you can feel perfectly healthy while having a chronic illness or life-limiting condition.
Without a definition of what health is that everyone can agree on, it is no wonder that coming up with an adequate test for it is challenging. “Sometimes, the simplest of questions are the hardest to answer,” says epidemiologist at the WHO.
Blood pressure and BMI
Ask your doctor and, assuming you don’t have any major complaints, they would probably start by taking your blood pressure and checking your BMI, a measure of weight that takes your height into account. But, on closer inspection, each has its problems.
In most high-income countries, a . Anyone with a BMI of 25 or over is considered overweight; beyond 30 they are classed as obese. But while it is uncontroversial that obesity is linked to conditions such as cardiovascular disease, stroke and type 2 diabetes, it is unclear where the cut-off should be for being classed as overweight.
Questions first arose in 2005, when a study showed that than those whose BMI was in the supposedly healthy range. Further doubts came in July from a large study of US adults showing that a over the study period compared with a BMI value in the supposedly healthier category of 22.5 to 24.9.
Blood pressure, meanwhile, is limited in the sense that it can only really tell you about a handful of conditions. With that said, it is still a good starting point, says Harris. “It can tell a doctor whether you have signs of cardiac disease or are anaemic, which a lot of people are.” She adds that regular, age-appropriate screening tests are also important for catching hidden conditions, such as cervical cancer.
So it isn’t as though the tests we have are useless. But as we have discovered more about the immense complexity of the human body, it has become increasingly clear that they can’t fully capture our deepening understanding of what it really means to be healthy.
Your microbiome
To get to grips with that, I spoke to , a geneticist at King’s College London who has dedicated much of his career to tracking people’s microbiomes – the myriad microbes that live in and on our bodies that have a huge impact on us, from our ability to digest food to our immune health, heart health and mood. Unsurprisingly, Spector’s first suggestion centres on just that. “If you want to know how healthy you are, the first thing you should do is test your microbiome,” he says. “Your microbiome reflects the health of most of the systems of the body. It’s a catch-all.”
The problem, until recently, was that we had no strong evidence of what a healthy gut microbiome looks like. The best advice was to aim for a good diversity of gut bacteria. In October, though, having analysed more than 100,000 microbiomes, Spector and his team announced that they had , the balance of which appears to be a good indicator of health. “If you’re looking for a holistic test of different aspects of health, then that’s the one to go for,” says Spector, who helped to develop Zoe, an app that offers these tests. When I do my own microbiome test, I get a score of 66 out of 100, which puts me in the “good” category, meaning I have a relatively healthy ratio of good to bad bacteria.
at the University of Nottingham, UK, thinks it is fair to say that there is a strong association between the microbiome and a number of chronic and acute conditions. It is also true that your gut bacteria can change dramatically in response to an infection, diet or chronic illness, she says, sometimes within days, so testing it can reflect your current health status.
Even so, microbiome testing does have its limitations, not least because “a specific microbiome composition isn’t good for everything for every person”, says Valdes. It is generally accepted that it is beneficial to have butyrate-producing bacteria, for instance, on the basis that they are involved in brain health, glucose tolerance and wound healing – and even prevent the proliferation of some cancer cells. If you have ulcers, however, butyrate can hinder their healing.
Spector’s second recommendation is to test your “metabolome”. This shows the breakdown products from metabolic processes, the chemical reactions in your body’s cells. The reason it makes for a good measure of health is that certain combinations of metabolites can be used as a marker of your current condition and future disease risk. Several companies offer such tests, which start at around £65.
Earlier this year, a group of international researchers combined metabolite data with blood fat data from more than 118,000 participants of UK Biobank – the world’s largest repository of metabolic biomarkers linked to health records – to create . The authors say that, although the striking similarity of some patterns of biomarkers across various diseases may pose problems for detecting specific conditions, metabolites are ideal for informing someone about their overall health.
Spector’s final recommendation is a test of biological age, in which you gauge how various aspects of your body are ageing compared with your chronological age. This pleases me because, five years ago, I got my “glycan age” tested. Glycans are complex carbohydrates that attach to other molecules in the body. Just how they glom onto an antibody called immunoglobulin G changes as we get older, which means they can be used to predict how fast your body is ageing relative to your years. My glycan age was 13 years younger than my actual age, which is good news because people who have high insulin levels, high cholesterol and other markers of ill health, also have an older glycan age.
All of which sounds satisfyingly scientific. But one of the things I really want to know is why my partner never seems to get sick when I am always coming down with something. Is his ability to sidestep a cold a sign that he is generally healthier than me?
Immune resilience
I was surprised to find that this isn’t the kind of question a lot of scientists seek to address. “They are more focused on treating disease than maintaining health,” says at the University of Texas Health Science Center at San Antonio. But he and his team have been attempting to better understand health, and what they have found suggests it partly comes down to immune resilience, or how well your immune system can deal with daily challenges.
By studying the blood cells of more than 40,000 people, Ahuja and his colleagues found that the balance between two types of immune cells called T-cells correlates with how you respond to physiological challenges, such as viruses or cancer. Those who responded best had a high level of a kind of T-cell called CD4, associated with resilience, and a low level of one called CD8, associated with inflammation, which is a vital process for eliminating pathogens but also underlies many diseases. They also looked at two sets of genes related to immune resilience and inflammation.
The researchers graded participants based on these metrics: grade 1 had the highest immune resilience, whereas grade 4 had the lowest. They found those with grade 1 were more likely to avoid symptoms from flu, more likely to resist being infected with HIV, had longer periods of time between recurrent skin cancers, were more likely to survive sepsis and covid-19, and had longer lifespans in general.
Women were more likely to have a better grade than men and, generally, everyone’s immune grades tended to worsen as they aged, or as they were exposed to infections or other illnesses. Intriguingly, however, there were some people in this cohort who maintained an excellent immune grade even into their 90s. “It might be a better reflection of health than age, when it comes to things like how you’ll react to covid-19,” says Ahuja. “We saw many older people who were grade 1 and immunologically healthier than a younger person who’s a grade 4.”
You can discover your immune grade with a simple blood test. If your T-cell ratio comes back worse than expected, it might be time to invest in a bit more exercise. Ahuja and his team gave a small group of people a 24-week exercise regime, taking their immune grade at various points throughout the study. In work that is yet to be published, they found that everyone’s immune grade improved by the end of the study. Then came the big reveal: after taking a two-week break from the regime, the whole group’s immune grade went back to baseline. “Evolutionarily, we weren’t designed to sit on our asses,” says Ahuja.
It is a tough pill to swallow, given my fickle relationship with exercise. I am beginning to think that I don’t want to take any more health tests. It is all starting to feel quite stressful, which brings us to mental health.
Harris says there are plenty of good tests online that assess your happiness, sleep, anxiety levels and such, screening you for everything from attention deficit hyperactivity disorder to depression, addiction and eating disorders. These are a good starting point, she says. If you are worried about your mental health, a single test isn’t going to cut it and you should see a doctor. But one way to take stock may be found closer to home: “Just ask the person who knows you best. We’ve found they are often the best person to tell you whether you seem [mentally] healthy or not,” says Harris.
Perhaps searching for a single comprehensive test is where I am going wrong. In their own quest for the hallmarks of health, at the University of Oviedo, Spain, and at the European Research Institute for Integrated Cellular Pathology in Paris came to the conclusion that such hallmarks aren’t confined to a particular molecule or even a whole system, but should be conceived as a series of “dynamic features that maintain the precarious equilibrium preceding disease”. In other words, health is homeostasis: the ability to rapidly correct things when they venture off-piste.
The pair’s includes things like your ability to heal after an injury, the speed at which you are able to correct your blood sugar after a dessert and the integrity of the physical barriers that help maintain your brain and body. Disruption of any of these derails our health, they say.
Their list of homeostatic processes is lengthy and impossible to test in full. But the research suggests we are on the right track with some of the aforementioned criteria – your immune resilience, for one. It also demonstrates the importance of skin health and other easy-to-test aspects of your physiology (see “Five quick ways to judge your health”, below).
Clearly, there is no all-encompassing test of health. But taken together, a handful of these new measures can offer a much clearer picture of what it means to be healthy and where a given person is at that moment. As for me, I can at least approach my 40th birthday feeling that I am in pretty good shape. I don’t have “complete well-being”, by any means, but I am happy and – as far as some of the most advanced tests can tell – reasonably healthy.
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FIVE QUICK WAYS TO JUDGE YOUR HEALTH
LOOK IN THE MIRROR
Your skin is an integral barrier that protects your body from a number of insults. Some researchers now suspect that wrinkles aren't only a result of ageing, but a cause of it too. As skin degrades, it produces zombie-like cells that spew out chemicals that flow around the body doing damage. So, if your skin is less youthful than that of others your age, it might be telling you something.
GET A GRIP
Several studies have determined that grip strength is a more powerful predictor of dying from cardiovascular disease than blood pressure, and that . Noticing a decrease in grip strength might be a red flag.
COUNT YOUR COLDS
In January, , an immunologist at the University of Sussex, UK, told żěè¶ĚĘÓƵ that the average person should expect to have one or two mild illnesses a year. If you get sick more than this, and if your illnesses last longer than other people's, it might be a sign that you aren't as healthy as you could be.
THINK ABOUT YESTERDAY
Think about how you feel today compared with last month. "Have you gone up or down a dress size? Has your sleeping pattern become better or worse?" says Margaret Harris at the World Health Organization. Comparing your current self to your past self offers a good insight into whether you are healthy – albeit using yourself as the benchmark.
ASK YOURSELF HOW YOU FEEL
Self-rated health scores correlate with many blood markers of health. But even when you control for these, people who subjectively "feel" better tend to live longer. Even among people with terminal cancer, those who rate their health as excellent . Research is ongoing to understand the nature of subjective health experience and what this tells us about our underlying health.
Helen Thomson is head of features at żěè¶ĚĘÓƵ
