Lead exposure linked to memory problems, even decades later

Historic lead levels from the era of leaded petrol may be contributing to cognitive issues 50 years later, according to research reported at the 2025 Alzheimer’s Association International Conference (AAIC).

Lead was originally added to petrol to increase performance, until researchers determined it posed serious risks to health and the environment. The phase-out of leaded petrol in the US began in 1975, when all new cars sold were required to have catalytic converters, and finally concluded on 1 January 1996.

“When I was a child in 1976, our blood carried 15 times more lead than children’s blood today,” noted Dr Esme Fuller-Thomson, a professor at the University of Toronto and Director of the Institute for Life Course & Aging, who served as senior author on the new study. “An astonishing 88% of us had levels higher than 10 micrograms per decilitre, which are now considered dangerously high.”

The study’s analysis of more than 600,000 adults aged 65 and older found that Americans are about 20% more likely to experience memory problems if they lived in areas with moderate to extremely high historical atmospheric lead levels (HALL) between 1960 and 1974, when leaded petrol use was at its highest. The researchers calculated the average HALL by area and linked it to self-reported memory problems from the American Community Survey from 2012–2017 (368,208 people) and 2018–2021 (276,476 people).

The researchers didn’t analyse the source of the lead, but they believe that the higher the density of automobile traffic, such as in urban areas, the higher the atmospheric lead. Factoring in both time periods, the researchers determined that 17–22% of people living in areas with moderate, high or extremely high atmospheric lead reported memory issues.

“Our study may help us understand the pathways that contribute to some people developing dementia and Alzheimer’s disease,” said lead author Dr Eric Brown, associate scientist and Associate Chief of Geriatric Psychiatry at the Centre for Addiction and Mental Health in Toronto. He suggested that those who have been exposed to atmospheric lead should focus on reducing other risk factors for dementia, including high blood pressure, smoking and social isolation.

Living near lead-polluting sites may affect memory

Another study reported at AAIC found that older adults who live within 5 km of a lead-releasing facility — such as glass, ready-mixed concrete, or computer and electronics manufacturers — are more likely to have memory and thinking problems than those who live further away. This research, which focused on a racially and ethnically diverse group of older adults, reinforces concerns about the long-term cognitive impact of environmental lead exposure, especially in communities already facing health disparities.

Researchers assessed 2379 patients (average age ~74 years) from two studies: the Kaiser Health Aging and Diverse Life Experienced study (KHANDLE, 1638 patients) of a diverse group of Kaiser Permanente insurance plan members who live in northern California, and the Study of Healthy Aging in African Americans (STAR, 741 patients) study of Black adults age 50 and older who live in the San Francisco and Sacramento areas. They evaluated the participants’ proximity to the nearest lead-releasing facility and compared the distance to participants’ Neuropsychological Assessment Scales results at baseline and two years later.

Compared to two years earlier, the KHANDLE participants who lived within 5 km of a lead-releasing facility scored 0.15 times lower on verbal episodic memory tests (recall of personal experiences) and 0.07 times lower on overall cognitive ability compared to those living further away. Every 5 km farther a participant lived from a lead-releasing facility was associated with 5% higher memory scores two years later. Among STAR group participants living within 5 km of a lead-releasing facility, researchers observed a 0.20 times lower score on semantic memory (general knowledge) two years later, compared to those who lived further away.

“Our results indicate that lead exposure in adulthood could contribute to worse cognitive performance within a few years,” said senior author Dr Kathryn Conlon, an associate professor of environmental epidemiology at the University of California, Davis. “Despite tremendous progress on lead abatement, studies have shown there is no safe level of exposure, and half of US children have detectable levels of lead in their blood. Additionally, there are regions and neighbourhoods that have more exposure.”

According to Conlon, there were 7507 lead-releasing facilities in the US in 2023. To reduce exposure, Conlon said people living near lead-producing facilities should keep their homes clean to avoid the accumulation of lead-contaminated dust, remove their shoes when coming inside, and place dust mats inside and outside to avoid tracking lead-contaminated dust indoors.

Lead exposure may set the stage for Alzheimer’s

Even low levels of lead exposure can create permanent changes in brain cells, including increased build-up of abnormal tau and amyloid beta — which are proteins associated with Alzheimer’s — according to a third study reported at AAIC.

Researchers exposed human brain cells to lead concentrations of zero, 15 and 50 parts per billion (ppb), simulating the kind of lead exposure people might experience through contaminated water or air (the US EPA’s action level for lead in drinking water is 15 ppb). The team ran molecular, genetic, biochemical and functional tests on the cells and determined the following:

• The 15 ppb and 50 ppb lead-exposed neurons were more electrically active (suggesting early dysfunction) than those that had no exposure.
• Energy-producing cells were damaged.
• There was an increase in tau and amyloid beta. Even after the lead was removed, the cells remained primed for damage, responding more severely to additional stressors such as tau.
   

“These findings help explain how lead exposure, especially in early life or from occupational and environmental sources, might leave a lasting molecular imprint on the brain, making it more vulnerable to age-related diseases like Alzheimer’s,” said lead author Dr Junkai Xie, a postdoctoral research associate in chemical engineering at Purdue University. “Our results show that lead exposure isn’t just a short-term concern; it may set the stage for cognitive problems decades later.”

Image credit: iStock.com/JDawnInk