The study, “Relationship between dementia and ankylosing spondylitis: A nationwide, population-based, retrospective longitudinal cohort study,” was published in the journal PLOS One.
Evidence has shown that people diagnosed with AS are at a higher risk of developing degenerative diseases, including cardiovascular or cerebrovascular problems, and mental disorders than the general population.
In fact, several studies have reported an association between AS and depression, anxiety, and sleep disturbances. However, whether AS increases the risk for dementia was not known.
Alzheimer’s disease is the most common cause of dementia, followed by vascular dementia, which is caused by lower blood supply to the brain due to diseased blood vessels.
Researchers in South Korea conducted a nationwide, retrospective analysis using data from the Korean National Health Insurance System database, surveyed from 2010 to 2014, to investigate a possible association between ankylosing spondylitis and dementia.
In total, they evaluated data from 14,193 people diagnosed with AS (71.75% men) and 70,965 age- and sex-matched people without AS who served as controls.
The participants’ demographic and clinical data was analyzed. The proportion of individuals with a low income, living in urban areas, and having additional diseases — such as diabetes, hypertension, and imbalance of fat (lipids) in the blood — were significantly higher in AS patients than in the control group.
The prevalence of overall dementia (1.37%) and Alzheimer’s dementia (0.99%) in the AS group was also significantly higher than in the control group (0.87% and 0.63%, respectively). Vascular dementia did not differ significantly between the two groups, despite AS patients having a higher incidence of cardiovascular problems.
“AS and dementia might be associated with diseases, sharing multiple causative illnesses. According to numerous studies, chronic uncontrolled inflammation has been known to be a mechanism responsible for not only AS but also psychiatric disorders including dementia,” the researchers wrote.
“The morbidity of psychiatric disorder in AS is high, due to symptoms such as chronic pain and functional impairment, and the association with depression and anxiety has already been revealed,” they added. As a result, this psychological status alone could be a direct cause of Alzheimer’s disease.
A third explanation for the observed link between AS and dementia is the fact that AS patients show increased levels of amyloid-beta protein in the blood, a hallmark of Alzheimer’s disease.
“The fourth hypothesis is related to the long-term persistent decline of physical activity in those with AS,” which, in turn, leads to decreased social, physical, and workforce activity. Because physical activity is known to have a significant impact on cognitive ability, “these conditions may lead to chronic psychological distress, which might result in dementia in old age, as a long-term outcome,” according to the researchers.
The team also looked at different risk factors, including age and gender, for dementia among AS patients, finding that those who are male or older than 65 years are associated with an increased risk for developing dementia.
Additionally, fair income (a household income greater than 20% of the median), urban residency, absence of diabetes, and absence of hypertension were also identified as risk factors for dementia in AS patients.
The results of this nationwide study “showed that AS patients have a significantly higher prevalence of overall dementia and Alzheimer’s dementia than the general population,” the researchers wrote.
“Comprehensive patient assessment using our subgroup analysis could help to prevent dementia in patients suffering from AS,” they concluded.