Living with an autoimmune disease may almost double the risk of mental health conditions including depression, anxiety and bipolar disorder, a study suggests.
The link may be explained by the chronic exposure to systemic inflammation that the autoimmune disease causes, researchers at the University of Edinburgh said.
A growing body of evidence suggests that inflammation is linked to mental ill health, but many of the published studies have relied on small sample sizes, limiting their statistical power.
To overcome this, researchers drew on data from 1.5 million people in the Our Future Health programme from across the UK. Participants completed a questionnaire that asked for personal, social, demographic, health and lifestyle information.
Health information included lifetime diagnoses for disorders including autoimmune and psychiatric conditions. Six autoimmune conditions were included in the study: rheumatoid arthritis, Graves’ disease (thyroid hormone disorder), inflammatory bowel disease, lupus, multiple sclerosis and psoriasis.
The mental health conditions the researchers were interested in were self-reported diagnoses of affective disorders, defined as depression, bipolar or anxiety disorder.
In total, 37,808 people reported autoimmune conditions and 1,525,347 did not. The lifetime prevalence of any diagnosed affective disorder was significantly higher among those with an autoimmune disorder than it was among the general population: 29% against 18%.
Similar associations emerged for depression and anxiety: 25.5% compared with just over 15% for depression, and just over 21% compared with 12.5% for anxiety. The prevalence of current depression and anxiety was also higher among people with autoimmune conditions.
While the prevalence of bipolar disorder was much lower, it was still significantly higher among those with autoimmune disorders than among the general population: just under 1% compared with 0.5%.
The prevalence of affective disorders was also significantly and consistently higher among women with autoimmune disorders than it was among men with the same physical health conditions: 32% compared with 21%.
The reasons for this are unclear. But the researchers, whose findings were published in the BMJ Mental Health journal, said theories suggest that sex hormones, chromosomal factors, and differences in circulating antibodies may partly explain the differences.
Overall, the risk for mental health conditions was nearly double in people with autoimmune conditions – between 87% and 97% higher. It remained high even after adjusting for potentially influential factors, including age, household income and parental psychiatric history.
The study was limited by a lack of available information on the time or duration of illness, making it impossible to determine whether autoimmune conditions preceded, co-occurred with or followed affective disorders.
No direct measurements of inflammation were made either, making it impossible to establish the presence, nature, timing or severity of inflammation.
The researchers concluded: “Although the observational design of this study does not allow for direct inference of causal mechanisms, this analysis of a large national dataset suggests that chronic exposure to systemic inflammation may be linked to a greater risk for affective disorder.
“Future studies should seek to determine whether putative biological, psychological, and social factors – for example, chronic pain, fatigue, sleep or circadian disruptions and social isolation – may represent potentially modifiable mechanisms linking autoimmune conditions and affective disorders.”
They added that it could be worth regularly screening people diagnosed with autoimmune diseases for mental health conditions, especially women, to provide them with tailored support early on.