A few months ago, I was infected by coronavirus and my first symptoms were bodily. But as the sore throat and cough receded, I was left feeling gloomy, lethargic and brain-foggy for about a week. An infection of my body had morphed into a short-lived experience of depressive and cognitive symptoms – there was no clear-cut distinction between my physical and mental health.

My story won’t be news to the millions of people worldwide who have experienced more severe or prolonged mental health outcomes of coronavirus infection. It adds nothing to the already weighty evidence for increased post-Covid rates of depression, anxiety or cognitive impairment. It isn’t theoretically surprising, in light of the growing knowledge that inflammation of the body, triggered by autoimmune or infectious disease, can have effects on the brain that look and feel like symptoms of mental illness.

However, this seamless intersection of physical and mental health is almost perfectly misaligned with the mainstream way of dealing with sickness in body and mind as if they are completely independent of each other.

In practice, physical diseases are treated by physicians working for medical services, and mental illnesses are treated by psychiatrists or psychologists working for separately organised mental health services. These professional tribes follow divergent training and career paths: medics often specialise to focus exclusively on one bit of the body, while psychs treat mental illness without much consideration of the embodied brain that the mind depends on.

We live in a falsely divided world, which draws too hard a line – or makes a false distinction – between physical and mental health. The line is not now as severely institutionalised as when “lunatics” were exiled to remote asylums. But the distinction remains deeply entrenched despite being disadvantageous to patients on both sides of the divide.

A 55 year old woman with arthritis, depression and fatigue, and a 25 year old man with schizophrenia, obesity and diabetes, have at least this in common: they will probably both struggle to access joined-up healthcare for body and mind. Psychological symptoms in patients with physical disease are potentially disabling yet routinely under-treated. Physical health problems in patients with major psychiatric disorders contribute to their shockingly reduced life expectancy, about 15 years shorter than people without them.

Why do we stick with such a fractured and ineffective system? I will focus on two arguments for the status quo: one from each side, from the tribes of medics and psychs.

For the medics, the problem is that we just don’t know enough about the biological causes of mental illness for there to be a deep and meaningful integration with the rest of medicine. Psychiatry is lagging behind scientifically more advanced specialities, such as oncology or immunology, and until it catches up in theory it can’t be joined up in practice. To which I would say yes but no: yes, greater detail about biological mechanisms for mental symptoms will be fundamental to the fusion of mind and body medicine in future; but no, that is not a sufficient defence of the status quo, not least because it discounts how much progress has already been made in making biomedical sense of illnesses such as schizophrenia.

When I started as a psychiatrist, about 30 years ago, we knew that schizophrenia tended to run in families; but it is only in the last 5-10 years that the individual genes conferring inherited risk have been identified. We were unsure whether schizophrenia was linked to structural changes in the brain; but MRI scanning studies have established beyond doubt that it is. We were puzzled that the risk of diagnosis was increased among young adults born in the winter months, when viral infections are more common; but now we can begin to see how the mother and child’s immune response to perinatal infection could disrupt the synaptic pruning process which is crucial to development of brain networks throughout childhood and adolescence.

For the psychs, the problem is fear of excessive reductionism: that the personal and social context of mental illness will be neglected in pursuit of an omnipotent molecule or other biological mechanism at the root of it all. That would indeed be a dead end, but it’s not a likely destination.

We have known since Freud that childhood experience can have a powerful effect on adult mental health. There is now massive epidemiological evidence that social stress, broadly speaking, and early life adversity in particular, are robust predictors of both mental illness and physical disease. Only a biomedical zealot in denial would claim this doesn’t matter. But the question remains: how does experience of poverty, neglect, abuse or trauma in the first years of life have such enduring effects on health many decades later?

Freud’s answer was that traumatic memories are buried deep in the unconscious mind. A more up-to-date answer is that social stress can literally “get under the skin” by rewriting the script for activation of the genetic blueprint. Molecular modifications called epigenetic marks cause long-term changes in the brain and behaviour of young rats deprived of maternal affection or exposed to aggression. Similar mechanisms could biologically embed the negative impacts of early-life adversity in humans, exacerbating inflammation and steering brain development on to paths that lead to mental health problems in future.

As things stand, these are plausible theories based on animal experiments rather than established facts in patients. But already they tell us this is not a zero-sum game. Drilling down on the biological mechanisms doesn’t mean that we must abandon or devalue what we know about the social factors that cause mental illness. Anxious anticipation of such a binary choice is itself a symptom of the divided way of thinking that we need to escape.

So, if we could entirely free ourselves from this unjustified class distinction between mental and physical health, what changes might we hope to see in future?

For medics and psychs, there will be more educational and career paths that cut across, rather than entrench, specialisations. Diagnostic labels categorically ordained by the bible of psychiatric diagnosis, the Diagnostic and Statistical Manual of Mental Disorders (DSM), will be reformulated in terms of the interactions between biomedical and social factors that cause mental symptoms. There will be new treatments to tackle the physical causes of mental illness, which are expected to be many and variable between patients, rather than trying to smother symptoms by “one size fits all” treatment regardless of cause. Knowing more about their physical roots, we should be much more successful at predicting and preventing mental health disorders.

For patients, the result will be better physical and mental health outcomes. There will be more integrated specialist physical and mental health services, like the new hospital we are planning in Cambridge for children and young people, so that body and mind can be treated under one roof throughout the first two decades of life. There will be more opportunities for people with relevant lived experience to co-produce research investigating the links between physical and mental health. But the biggest impact of all could be on stigma. The sense of shame or guilt that people feel about being mentally ill is an added load, a meta-symptom, culturally imposed by the false dichotomy between physical and mental health. Without it, the stigma of mental illness should fade away, just as the stigma attached to epilepsy tuberculosis and other historically mysterious disorders has been diminished by an understanding of their physical causes.

Ultimately it is easier to imagine a better future for mental and physical health together than for either alone.

• Edward Bullmore is professor of psychiatry at the University of Cambridge and author of The Inflamed Mind (Short Books Ltd, £9.99). To support The Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.

Further reading

Inventing Ourselves: The Secret Life of the Teenage Brain by Sarah-Jayne Blakemore (Black Swan, £9.99)

The Body Keeps the Score: Mind, Brain and Body in the Transformation of Trauma. by Bessel van der Kolk (Penguin, £12.99)

Illness as Metaphor & Aids and its Metaphors by Susan Sontag (Penguin Classics, £14)