Pencil erases the human brain. Certain autoimmune diseases, including rheumatoid arthritis, can carry added risks of dementia, according to new research published in the Journal of Epidemiology & Community Health.

When they compared about 7 million English control patients admitted to hospitals for other reasons between 1998 and 2012 with 1.8 million admitted with autoimmune diseases — including 316,043 with rheumatoid arthritis — researchers found the latter were 20 percent likelier to be readmitted for dementia.

“The associations with vascular dementia may be one component of a broader association between autoimmune diseases and vascular damage,” the researchers wrote. “Clinicians should be aware of the possible coexistence of autoimmune disease and dementia in individuals.”

“This is an epidemiology study using the power of big numbers of patients to look at a hypothesis, namely that Alzheimer’s disease may have an autoimmune component, and our bottom line in epidemiological and population terms is that yes, the study supports that hypothesis,” Michael Goldacre, professor emeritus of public health at University of Oxford and study author, told Medscape.

Patients with rheumatoid arthritis had an elevated risk for vascular dementia — which may be caused by brain damage following strokes or injury to the blood vessels that lead to the brain — but not for Alzheimer’s, the study found. The rate ratio for vascular dementia for RA patients was 1.16, whereas it was just 0.89 for Alzheimer’s (AD).

“We might have been tempted to just dismiss the seemingly protective effect — the inverse relationship between RA and AD — were it not for the fact that others have reported on that before, so it’s not an entirely sort of eccentric finding,” Dr. Goldacre told Medscape.

Dr. Goldacre and colleagues speculate that nonsteroidal anti-inflammatory drug (NSAIDs) use may protect against Alzheimer’s. “People with rheumatoid arthritis generally take NSAIDs to manage their condition, so if rheumatoid arthritis is at least partially a proxy for NSAID use, the real association may be between NSAID use and a reduced risk of AD,” they write.

Prior research also shows associations between arthritis and dementia. A 2015 study found that osteoarthritis patients were at higher dementia risk than those without OA; and a 2013 study revealed associations between midlife RA and worse cognitive status two decades later.