Conditions where the immune system attacks healthy cells might increase dementia risk.
Dementias are a range of conditions, the most prevalent of which is Alzheimer's. They are characterized by a progressive loss of memory function and other cognitive skills, eventually leading to an inability to perform everyday activities.
Currently, an estimated 47.5 million people are living with dementia, worldwide. Due to increasing lifespans, this figure is predicted to triple by the year 2050.
This steep rise in the number of cases is being referred to by some as a dementia epidemic, and for this reason, there is a great deal of focus on identifying the precise causes.
Certain factors are known to increase the risk of dementia. Advanced age, alcohol use, diabetes, and hypertension (high blood pressure) have all been said to contribute to this risk. However, there is still much to learn about how and why dementia arises.
Autoimmune disease and dementia
Over recent years, another potential risk factor has received some attention: autoimmune diseases.
Autoimmune diseases are conditions in which the body's own immune system attacks healthy cells and tissues. Some evidence has shown that individuals with these types of diseases have an increased risk of developing dementia.
A research team from the University of Oxford in the United Kingdom set out to examine this question in more detail. Utilizing hospital admissions data taken from U.K. hospitals between 1998 and 2012, they investigated whether being admitted to a hospital with one of 25 autoimmune diseases was associated with an increased risk of a dementia admission later in time.
Across the 14-year time sample, there were more than 1.8 million admissions to hospitals because of an autoimmune disorder. This included more than 300,000 people with rheumatoid arthritis (RA) and around 1,000 with Goodpasture's syndrome, a rare condition that attacks the lungs and kidneys.
Increased dementia risk identified
Once the data were analyzed, the researchers found that an initial admission due to an autoimmune condition increased the risk of a later admission due to dementia by 20 percent.
Of the 25 autoimmune conditions analyzed, 18 were shown to be significantly associated with dementia. These include:
- Addison's disease - 48 percent increased risk
- Polyarteritis nodosa - 43 percent increased risk
- Multiple sclerosis - 97 percent increased risk
- Psoriasis - 29 percent increased risk
- Systemic lupus erythematosus - 46 percent increased risk
- Thyrotoxicosis - 31 percent increased risk.
The majority of these associations were still significant 5 or more years after the initial admission for an autoimmune disease. In other words, the dementia was not picked up during the initial hospital examination.
Although the exact dementia diagnosis was not always noted, the risk was 6 percent higher for Alzheimer's and 28 percent higher for vascular dementia.
The researchers believe that the higher risk associated with vascular dementia might be due to associations between autoimmune diseases and risk factors for cardiovascular and cerebrovascular diseases in general.
An interesting exception to these results was RA; in this case, a hospital admission for RA seemed to protect against Alzheimer's disease. The researchers believe that this might be due to the nonsteroidal anti-inflammatory drugs often taken by individuals with RA, such as aspirin and paracetamol. These medications have previously been shown to reduce Alzheimer's risk.
"If our findings are confirmed in other studies, clinicians and epidemiologists will wish to know that some people with some autoimmune diseases have an elevated risk of dementia."
The study is observational and, therefore, cannot prove cause and effect. Furthermore, although the large sample size makes the interaction worthy of further study, as the authors emphasize, the effect size was small. The authors write that their "findings should be considered as indicative rather than definitive."