A study of over 22 million people has found that autoimmune diseases now affect around one in 10 individuals and could, in some instances, be driven by environmental factors like smoking and obesity.

Some 19 of the most common autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis and multiple sclerosis, have been shown to affect 13% of women and 7% of men.

The findings, published in The Lancet,  highlight variations in the incidence of some autoimmune diseases across socioeconomic backgrounds, seasons and regions, suggesting that disease variance could be linked to modifiable risk factors such as smoking or obesity.

Autoimmune diseases occur when the body’s immune system is disturbed and attacks normal healthy cells rather than fighting infections. There are more than 80 known autoimmune diseases, and some disorders, such as type 1 diabetes, have increased in prevalence over the past several decades. 

In this new study, scientists working in epidemiology, biostatistics, rheumatology, endocrinology and immunology came together from the UK and Belgium to examine who is most affected by these conditions, how different autoimmune diseases may co-exist and why there has been an overall rise in immune disorders.

Using anonymised electronic health records from Clinical Practice Research Datalink (CPRD) in the UK, the researchers investigated the prevalence of 19 of the most common autoimmune diseases in 22,009,375 individuals between 2000 and 2019.

The findings show that around 10% of the population are affected by autoimmune conditions, higher than previous estimates, ranging between 3-9%. Women were found to have a higher prevalence of disorders than men, with 13% of the female population affected compared to 7% of the male population.

The research also confirmed evidence of socioeconomic, seasonal, and regional disparities among several autoimmune disorders. In some cases, a person with one autoimmune disease was more likely to develop a second than someone without an autoimmune disease. This was particularly visible among rheumatic diseases and endocrine diseases.

The researchers suggest that the variations could be attributable to lifestyle factors such as smoking, obesity or stress rather than genetic differences alone. This phenomenon could not be generalised across all autoimmune diseases, with diseases such as multiple sclerosis having low rates of co-occurrence with other autoimmune disorders, suggesting a distinct pathophysiology.

Professor Geraldine Cambridge, from University College London, said: ‘Our study highlights the considerable burden that autoimmune diseases place upon individuals and the wider population. Disentangling the commonalities and differences within this large and varied set of conditions is a complex task.’

Dr Nathalie Conrad, from the University of Oxford, added: ‘We observed that some autoimmune diseases tended to co-occur with one another more commonly than would be expected by chance or increased surveillance alone. This could mean that some autoimmune diseases share common risk factors, such as genetic predispositions or environmental triggers.’

The researchers highlight a ‘crucial need’ to increase research efforts to understand the causes of these diseases in order to support the development of targeted interventions to reduce the contribution of environmental and social risk factors.

This article first appeared on our sister title Nursing in Practice.