When I was still practising, autoimmune diseases were rare and exotic. There has been a remarkable change. Now they affect one in 10 people. Why should this be?

Well, for starters, the findings of a study highlight seasonal, regional and socioeconomic differences for several autoimmune disorders, providing new clues as to what factors may be involved in causing these conditions. What’s an autoimmune disease? It occurs when a trigger causes the immune system to mistakenly attack normal healthy cells in the body.

There are more than 80 known autoimmune diseases, including rheumatoid arthritis, type 1 diabetes and multiple sclerosis. The exact causes of autoimmune diseases remain largely unknown, including the role genetics play and how much is down to environmental factors.

To answer these questions, a consortium of researchers from UCL, the University of Glasgow, Imperial College London, Cardiff University, the University of Leicester, Oxford University and KU Leuven came together. The group included experts in epidemiology, biostatistics, ­rheumatology, endocrinology and immunology.

The study used anonymous data from 22 million Britons to investigate 19 of the most common autoimmune diseases by examining whether numbers of autoimmune diseases are rising, who is most affected, and how different autoimmune diseases may co-exist with each other.

They found these 19 autoimmune diseases affect around 10% of the population and in more women (13%) than men (7%). The research uncovered socio-economic, seasonal and regional disparities for several autoimmune disorders, suggesting they’re unlikely to be caused by genetic differences alone. This may point to other, ­potentially modifiable, risk factors such as smoking, obesity and stress.

In some cases a person with one autoimmune disease is more likely to develop a second, compared to someone without one. Dr Nathalie Conrad of Oxford University said: “We observed that some autoimmune diseases tended to co-occur more commonly than would be expected by chance or increased surveillance alone.

“This could mean some autoimmune diseases share common risk factors, like genetic predispositions or ­environmental triggers. This was particularly visible among rheumatic and endocrine diseases. But this phenomenon was not generalised across all autoimmune diseases. Multiple sclerosis, for example, stood out as having low rates of co-occurrence with other auto-immune diseases, suggesting a distinct pathophysiology.”

These findings reveal novel patterns that will inform the design of further research into possible causes. Professor Geraldine Cambridge of UCL commented that disentangling the similarities and differences within this large and varied set of conditions is a complex task but in the end could lead to targeted interventions.