Infections may do more than run you down, make you feel miserable and cause absences from work or school: A new study finds that having a long track record of infections may bite into your mental reserves as well.

Scientists have long suspected that infections wreak havoc not just on the body but on the mind as well, and it doesn’t seem to matter whether the infections are viral or bacterial, or what part of the body they affect. Having a medical history that includes more than the usual infections puts a patient at higher risk of stroke and vascular disease. And poorer vascular health has been linked to Alzheimer’s disease and other dementia risk.


But a new study, published Monday in the journal Neurology, takes the reasonable next step of linking infections directly to poorer cognitive function and does so in a large, multiethnic population that was stroke-free at the outset of the study.

When it comes to infections, the blood carries a scorecard of those that have come and gone through the years. After the immune system has gone a round or two with pathogens such as of Chlamydia or Mycoplasma pneumoniae, Helicobacter pylori, cytomegalovirus or herpes simplex virus type 1, it develops antibodies that attest to the struggle. Researchers used those telltale signs of past infections to assign each subject an infectious burden index.


From a group of 3,298 New York City residents 40 years of age or older, researchers from Columbia University and from University of Miami’s Miller School of Medicine gathered and had blood samples analyzed. The group’s average age was 69 years old and 58% were Latino. The same subjects were given a 30-point mini-mental status exam, a standard screening used by neurologists to detect cognitive problems in patients. The researchers repeated the cognitive screen yearly for several years.

African American and Latino subjects in general had higher infectious burden indices than did white non-Latino participants, and those with less than a high school education, who did not consume alcohol and had no heart disease also had evidence of having had more infections.


On average, the higher a subject’s infectious disease burden was, the lower his or her score was on the mini-mental exam. The effect was particularly marked for women and for those who were physically inactive. The more active a subject with a long history of infections was, the higher his or her mental function appeared to be, leading the authors to suggest that for those who have suffered a lot of past infections, regular exercise might be key to countering their ill effects on cognition.

The authors surmised that inflammation is the common factor that links infection history and poorer mental performance. When the immune system gears up for a fight, it send an army of inflammatory agents out across the body, as well as into the brain. Those agents take their toll on the linings of veins and arteries and have long been suspected of wreaking particular havoc in the brain.


On the plus side, researchers found that over the years they tracked their subjects, those with higher disease burdens and lower mental performance didn’t experience further mental decline any faster or steeper than did those who had gotten fewer infections.