Chronic infection—already known to be associated with heart disease—has been linked to cognitive impairment, according to a recent study by Dr. Mira Katan and colleagues from the department of neurology at Columbia University. The researchers tested 1,625 subjects, with an average age of 69, using the Mini-mental State Examination (MMSE) ; they also tested each member of the group for their infectious burden (IB), that is, their degree of exposure to five common viruses and bacteria. The researchers conclude that “A measure of IB associated with stroke risk and atherosclerosis was independently associated with cognitive performance in this multiethnic cohort. Past infections may contribute to cognitive impairment” ( Neurology , March 26, 2013 ). The link between IB and cognitive impairment was stronger among women, those with lower levels of education, those without health insurance or Medicare, and those who did not exercise. The reasons for the association are less clear, according the Dr. Katan. “Another mechanism might be that these pathogens are neurotoxic, directly affecting the nerves,” she said in March 29 New York Times interview . “We’ve found a common pattern but we cannot prove causality.” Although further study is needed, the results could lead to identifying individuals who are at risk of cognitive impairment—and taking action to lower that risk.