The largest increases in autoimmune disorders among 22 million individuals in the United Kingdom are in celiac disease, Sjogren's syndrome, and Graves' disease, according to recent findings.¹

The findings indicated that there is an increasing prevalence and burden of autoimmune diseases. Additionally, this study showed that environmental influences in the conditions’ development and their co-occurrence with other conditions are more apparent.²

These findings were the result of research into the incidence and prevalence of 19 common autoimmune diseases of patients in the UK. This research was also conducted to assess disease trends and demographic factors among patients.

The research was authored by Nathalie Conrad, PhD, from the Department of Public Health and Primary Care at Katolieke Universiteit Leuven in Belgium. Conrad and her team noted that modern estimates of autoimmune disease incidence and trends are generally both scarce and inconsistent.

“We aimed to investigate the incidence and prevalence of 19 of the most common autoimmune diseases in the UK, assess trends over time, and by sex, age, socioeconomic status, season, and region, and we examine rates of co-occurrence among autoimmune diseases,” Conrad and colleagues wrote.

Background and Findings

The investigators made use of linked primary as well as secondary electronic health records drawn from the Clinical Practice Research Datalink (CPRD). This is a cohort that is known to be representative of the population of the UK as far as sex, ethnicity, and age.

The research team used data on both men and women without any age restrictions, and participants were required to have acceptable records, approval for linkage with Hospital Episodes Statistics and Office of National Statistics, and to be registered with their general practice for a minimum of 12 months during the study period.

The team calculated the standardized incidence and prevalence rates of 19 autoimmune disorders between 2000 - 2019, and they employed negative binomial regression models to explore temporal trends and variations based on factors such as sex, socioeconomic status, age, season of onset, and geographical region specifically within England.

In order for them to examine the simultaneous occurrence of autoimmune diseases, the investigators utilized negative binomial regression models to calculate incidence rate ratios (IRRs).

These then allowed the team to compare the incidence rates of coexisting autoimmune diseases among individuals who had already been diagnosed with a primary autoimmune disease, with the incidence rates observed in the general population. They also adjusted these calculations for sex and age to ensure accurate comparisons.

The investigators included a total of 22,009,375, out of which 978,872 were found to have received a new diagnosis of at least a single autoimmune disease between January of 2000, and June of 2019. They noted that the mean age of those diagnosed was shown to be 54.0 years (standard deviation 21.4), with 63.9% being female and 36.1% being male.

During the study period, the investigators reported an increase in age and sex standardized incidence rates of autoimmune diseases.

The largest increases the team observed were in celiac disease, Sjogren's syndrome, and in Graves' disease, with incidence rate ratios being in the range of 2.07 - 2.19. Conversely, pernicious anemia and Hashimoto's thyroiditis had a substantial decrease in incidence.

Overall, the 19 autoimmune disorders examined affected 10.2% of the population during the study period—13.1% of women and 7.4% of men. There was a socioeconomic gradient observed for several diseases, including Graves' disease, pernicious anemia, rheumatoid arthritis, and systemic lupus erythematosus, indicating a higher incidence in regions known to be more deprived.

Seasonal variations were found in the diagnosis of childhood-onset type 1 diabetes (more commonly diagnosed in winter) and vitiligo (more commonly diagnosed in summer). Regional variations were also observed for various autoimmune conditions.

Autoimmune disorders showed significant associations with each other, particularly Sjögren's syndrome, systemic lupus erythematosus, and systemic sclerosis. Those with childhood-onset type 1 diabetes were found to have higher rates of celiac disease, Addison's disease, and thyroid diseases, while multiple sclerosis had a lower rate of co-occurrence with other autoimmune disorders.

These findings on autoimmune conditions and their burden over time strongly indicate that there are environmental factors to consider in disease pathogenesis.

“The inter-relations between autoimmune diseases are commensurate with shared pathogenetic mechanisms or predisposing factors, particularly among connective tissue diseases and among endocrine diseases,” they wrote.

References

1. ^{Conrad N, Misra S, Verbakel JY, et al. Incidence, prevalence, and co-occurrence of autoimmune disorders over time and by age, sex, and socioeconomic status: a population-based cohort study of 22 million individuals in the UK. The Lancet. [Online ahead of print]. Accessed May 16, 2023. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(23)00457-9/fulltext.}
2. ^{Somers EC, Thomas SL, Smeeth L, Hall AJ. Autoimmune diseases co-occurring within individuals and within families: a systematic review. Epidemiology. 2006 Mar;17(2):202-17. doi: 10.1097/01.ede.0000193605.93416.df. PMID: 16477262.}