Lead in Gasoline Tied to Cognitive Impairment

Exposure to moderate levels of lead from gasoline during the 1960s and early 1970s is linked to a 20% increased risk for memory problems later in life, preliminary findings from a large, novel study showed.

Investigators found that older adults living in areas with moderate-to-extremely high historical atmospheric lead levels (HALLs) reported higher rates of memory problems than those living in areas with low lead exposure. These associations remained consistent across two periods and after adjusting for key demographic factors.

“In someone who’s presenting with a memory problem, it’s very important to think broadly about possible causes, and that can include lead exposure,” study investigator Eric Brown, MD, associate scientist and associate chief of geriatric psychiatry, Centre for Addiction and Mental Health, Toronto, Ontario, Canada, told Medscape Medical News.

The findings were presented on July 27 at the Alzheimer’s Association International Conference (AAIC) 2025.

First Study of Its Kind

Previous research has shown lead exposure is toxic to the brain, and high exposure can cause cognitive impairment. A major source of lead exposure in the 1960s and 1970s was atmospheric pollution due to leaded gasoline.

With growing evidence of its health risks, lead was removed from gasoline and completely phased out by the ‘80s and ‘90s. However, research suggests that half the US population — more than 170 million older people — had already been exposed to high lead levels in childhood.

It is important to understand the link between cognitive impairment and past lead exposure, said Brown. “Did this exposure have an impact on rates of dementia, and if it did, is there something we can learn from it?”

As previously reported by Medscape Medical News, a 2024 study linked leaded gas exposure to 151 million excess cases of mental illness over a 75-year period.

Between 1940 and 2015, the data showed that those most exposed to lead — Generation X, who were born between 1966 and 1986 — had the largest increases in mental health issues. Those born between 1966 and 1970 were most affected, aligning with the peak use of leaded gasoline during that time, researchers noted.

However, Brown said his team’s study is the first to look at exposure to atmospheric lead across the US as a risk factor for dementia.

Lead Burden and Memory

The study mapped HALLs using measurements obtained by the US Environmental Protection Agency from 1960 to 1974, a period of high leaded gasoline combustion. Perhaps not surprisingly, the highest rates of exposure were in large urban areas that had more automotive traffic.

Researchers calculated the mean HALL for each Public Use Microdata Area (PUMA) — a geographic unit used by the US Census Bureau to gather statistical and demographic information. The analysis included only PUMAs that contained at least one lead measurement in the period 1960-1974.

The investigators also obtained data on self-reported memory problems from the American Community Survey, an annual demographics survey conducted by the Census Bureau, in two periods: 2012-2017 (n = 368,208) and 2018-2021 (n = 276,476). The samples included respondents aged 65 years or older living in the area where they grew up.

The study compared individuals living in PUMAs with moderate (0.4-0.79 μg/m³), high (0.8-1.19 μg/m³), and extremely high (≥ 1.2 μg/m³) HALLs to those in areas with the lowest exposure (< 0.4 μg/m³). Analyses were adjusted for demographic factors including age, sex, ethnicity, and education.

Compared with those living in PUMAs with the lowest HALL, the odds of memory impairment in 2012-2017 were higher in those in PUMAs with moderate (odds ratio [OR], 1.21; 95% CI, 1.17-1.25), high (OR, 1.21; 95% CI, 1.17-1.25), and extremely high HALL levels (OR, 1.19; 95% CI, 1.13-1.25).

Using 2018-2021 data, investigators found comparable outcomes for older adults living in PUMAs with moderate (OR, 1.17; 95% CI, 1.12-1.21), high (OR, 1.20; 95% CI, 1.16-1.25), and very high HALL (OR, 1.22; 95% CI, 1.15-1.29).

While the total number of people with dementia continues to rise due to an aging population, dementia rates are declining. Brown questioned whether this trend may be due, in part, to lead emission controls implemented decades ago.

It is important to learn the cognitive impact of lead exposure because there are now potential treatment options, said Brown. “If we understand all the risk factors, there could be different ways to stratify people for particular treatments.”

Multiple Sources of Exposure

Although leaded gasoline has been phased out, lead exposure remains a concern due to its presence in paint, plumbing, and water distribution systems — as seen in Flint, Michigan, where drinking water was contaminated with lead about a decade ago.

The risks are particularly acute for vulnerable populations, such as those who are economically and socially disadvantaged and Indigenous hunters, who may be exposed through consumption of wild game contaminated by lead bullets, Brown noted.

He and his research team aim to look further into the dataset to assess different periods and other sources of air pollution and to use other datasets to look at dementia diagnoses rather than self-reported memory problems.

A second study presented at the AAIC suggests that lead exposure in adulthood — not just childhood — may be linked to cognitive decline. Researchers found that older adults living near lead-emitting facilities, such as glass, ready-mixed concrete, or electronics manufacturers, had poorer cognitive performance 2 years later.

The analysis drew on a diverse sample of 2409 participants from two harmonized cohorts: the KHANDLE study and the STAR.

Researchers assessed participants’ proximity to the nearest lead-releasing facility and evaluated cognitive performance — specifically executive function, verbal episodic memory, and semantic memory — 2 years later using the Spanish and English Neuropsychological Assessment Scales.

The average age at cognitive testing was 74 years, with 62% of the sample identifying as women. The cohort was racially and ethnically diverse: 48% identified as Black, 17% as Asian, 14% as Latinx, and 20% as non-Hispanic White.

Living within 5 km of a lead-emitting facility was associated with significantly poorer cognitive outcomes: a 0.15 SD lower episodic memory score (95% CI, -0.24 to -0.06) and a 0.20 SD lower semantic memory score (95% CI, -0.39 to -0.02).

“Our results indicate that lead exposure in adulthood could contribute to worse cognitive performance within a few years,” study investigator Kathryn Conlon, PhD, associate professor of environmental epidemiology, School of Medicine, University of California, Davis, said in a press release.

“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 neighborhoods that have more exposure.”

In 2023, there were 7507 lead-releasing facilities across the US, many of them located in densely populated areas, said Conlon.

A third study presented at the AAIC showed that even low levels of lead exposure can cause permanent changes in brain cells, including increased accumulation of abnormal tau and amyloid beta. These findings suggest a biologic link between lead exposure and Alzheimer’s disease.

Toward Risk Reduction

Commenting for Medscape Medical News, Rebecca M. Edelmayer, PhD, vice president of Scientific Engagement at the Alzheimer’s Association, said this research contributes to the efforts to understand dementia risk across the life course.

“These are the kinds of things that are critical for us to study. Defining what puts people at risk, potentially lead in this case, is the first step, but then evaluating an intervention to reduce someone’s risk across their life course is going to be the next step.”

The aim, she added, is to develop “sustainable and achievable recommendations for risk reduction and potentially even prevention.”

The study had no outside funding, and the investigators disclosed having no relevant financial disclosures.