We are trained, all of us in the health care field, to think in categories. The cardiovascular concern goes one way, the metabolic one another, the mental health one somewhere else again. It is how medicine is organised, how services are commissioned, how our own assessments are structured. But sit with the working age population long enough, as many of us do, and the categories start to look less like separate problems and more like separate windows onto the same room. 

Most chronic disease is the late expression of a single underlying biology. Beneath the type 2 diabetes, the hypertension One biology – many disease, the fatty liver, the early cognitive change, the low mood, the stubborn weight, runs a common process, smouldering chronic inflammation, driven by metabolic dysfunction and deeply entangled with the gut microbiome. The endpoints differ because they surface in different tissues at different times. The process upstream of them is largely shared. 

The mechanisms are increasingly well described. Excess visceral fat behaves less like inert storage and more like an active organ, releasing inflammatory signals into the circulation. Insulin resistance builds quietly, for years, while routine tests still read normal. The gut microbiome, shaped by how we eat and how we live, either calms that inflammation or feeds it. Over a decade or two the same slow fire surfaces as a cardiac problem in one person, a metabolic one in another, a cognitive one in a third. 

Looking earlier, before disease appears 

What follows from this is a shift in when we look, not only in what we look for. If the process begins in the forties, and sometimes earlier, then the assessment that matters most is the one carried out while a person still feels entirely well. By the time a diagnosis arrives we are documenting an outcome that was already decades in the making. The upstream view moves our attention forward in time, into the years when the biology is still quiet, still hidden from the standard test, and still genuinely open to change. It is an uncomfortable reframing, because it asks us to take seriously people who have nothing yet to show for the risk they carry. It is also the only point at which prevention is truly prevention. 

Why this matters for occupational health? 

Why does this matter for occupational health in particular? Because a shared cause is a shared point of intervention. If we treat each diagnosis as a separate event, we are always downstream, managing consequences one at a time, arriving after the damage is done. If we recognise the common biology, we can act once, early, on the process that drives all of it. That is a fundamentally different proposition, and our position in the working age population is what makes it possible. 

It also explains something we all encounter, the employee who collects diagnoses. First the raised blood pressure, then the borderline glucose, then the low mood, then the disturbed sleep, each managed by a different pathway, each treated as its own piece of bad luck. Seen through the upstream lens this is not a run of unrelated misfortune. It is one biology expressing itself, predictably, over time. And it is genuinely modifiable, through what we eat, how we sleep and how we move, when it is caught while it is still upstream. 

None of this replaces the specialist pathways we depend on. The cardiologist, the endocrinologist, the psychiatrist remains essential once disease is established. The upstream view simply asks a question that sits before all of them. What if a good deal of what we currently wait to diagnose could be changed years earlier, at the level of the shared cause, rather than managed separately once it has surfaced? 

For a discipline that meets working age adults before anyone else, that question is not academic. It is the beginning of a different kind of practice, one that looks for the fire rather than cataloguing the smoke, and the reward for finding it early is measured in decades of energy, sharpness and capacity. Next blog I want to ask why the health checks we currently rely on so often miss that fire entirely.