Researchers striving to understand the origins of dementia are building the case against a possible culprit: lead exposure early in life. A study spanning 23 years has now revealed that monkeys who drank a lead-rich formula as infants later developed tangles of a key brain protein, called tau, linked to Alzheimer’s disease. Though neuroscientists say more work is needed to confirm the connection, the research suggests that people exposed to lead as children—as many in America used to be before it was eliminated from paint, car emissions, water, and soil—could have an increased risk of the common, late-onset form of Alzheimer’s disease.

Even in small doses, lead can wreak havoc on the heart, intestines, kidneys, and nervous system. Children are especially prone to its pernicious effects, as it curbs brain development. Many studies have linked early lead exposure with lower IQs. Researchers estimate that one in 38 children in the United States still have harmful levels of the metal in their systems, but evidence linking this exposure to dementia later in life has been tenuous.