Exposure to a toxic metal as far back as childhood could raise the risk of developing dementia later in life, a first-of-its-kind study suggests.

Researchers in Canada studied more than 600,000 older US adults who were exposed as children to high levels of lead, a toxic metal linked to autism, infertility and cancer.

They found people who grew up in the 1960s and 70s – when the use of lead in gasoline and paint was commonplace and unregulated – were 20 percent more likely to have memory issues later in life.

These memory issues could develop into mild cognitive decline, a precursor to several forms of dementia, including Alzheimer’s disease – the most common form which affects nearly 7 million Americans.

Additionally, nearly nine in 10 Americans growing up at the time had ‘dangerously high’ levels of lead in their blood, suggesting damning long-term consequences for older Americans.

The research, unveiled at the world’s largest dementia conference this week in Toronto, suggests the exposure is likely tied to leaded gasoline, which took nearly two decades to be phased out of cars sold in the US.

However, the metal still lurks in older houses, meaning younger generations could face the same dementia risk.

Additional US-based studies revealed at the conference found even small levels of lead exposure could lead to more amyloid and tau plaques – which cause Alzheimer’s disease – forming in the brain.

Lead exposure dating to childhood could increase the risk of memory issues

Dr Maria C Carrillo, chief science officer and medical affairs lead of the Alzheimer’s Association, who was not involved in the studies, said: ‘Research suggests half the US population – more than 170 million people – were exposed to high lead levels in early childhood. 

‘This research sheds more light on the toxicity of lead related to brain health in older adults today.’

The results come as nearly 9 million adults in the US are living with some sort of dementia.

The first study, from researchers at the University of Toronto, looked at approximately 600,000 US adults sourced from the American Community Survey.

The participants, all over the age of 65, were exposed to historically atmospheric levels of lead (HALL) between 1960 and 1974.

The researchers did not analyze the source of the lead but believe that a higher density of automobile traffic, such as in urban areas, was the main contributor.

The team determined that 17 to 22 percent of people living in areas with moderate, high or extremely high atmospheric lead reported memory issues.

This translated to a 20 percent increased risk of memory problems compared to those without high lead exposure.

Dr Eric Brown, lead study author and associate chief of geriatric psychiatry at the Centre for Addiction and Mental Health, Toronto, said: ‘Our study may help us understand the pathways that contribute to some people developing dementia and Alzheimer’s disease.’

When lead enters the body, it travels through the bloodstream and spreads to vital organs, including the brain. Once there, it infiltrates cells responsible for nutrients like calcium and iron, causing permanent damage. 

There is no safe level of lead, according to the CDC. 

For decades, lead was added to paint, pipes and even some children’s toys. 

The researchers noted it was also used in gasoline to improve performance, and the process to phase it out did not start until 1975. It took roughly 20 years to fully remove lead from gasoline.

Dr Esme Fuller-Thomson, senior study author and professor at the University of Toronto, said: ‘When I was a child in 1976, our blood carried 15 times more lead than children’s blood today.

‘An astonishing 88 percent of us had levels higher than 10 micrograms per deciliter, which are now considered dangerously high.’ 

The researchers warned while atmospheric lead levels have decreased, the metal can still be found in older homes without updated paint or pipes. 

In fact, roughly 38 million homes throughout the country (one in four) were built prior to lead paint bans and may still contain the paint on windowsills, doorframes, stairs, railings, porches and fences.

The EPA also estimates there are still about 9 million lead pipes in use across the US. 

Dr Brown urged those who have been exposed to atmospheric lead to focus on reducing other risk factors for dementia, including high blood pressure, smoking and social isolation.

The researchers tied high lead exposure to gasoline used in the 1960s and ’70s

An additional study presented this week at the Alzheimer’s Association International Conference found that older adults who live within three miles of a lead-releasing facility were more likely to have memory and thinking issues than those who lived further away.

These facilities include those that manufacture glass, mixed concrete or computers and other electronics. 

The team, from the University of California, Davis, assessed 2,379 older patients who had an average age of 74. All lived in California and were taken from two studies. 

Compared to two years earlier, participants who lived three miles from a lead-releasing facility scored lower on verbal episodic memory tests – recalling personal experiences – and overall cognition than those who lived further away. 

And every three miles farther a participant lived from one of these facilities, their memory scores improved an additional five percent. 

Dr Kathryn Conlon, senior study author and associate professor of environmental epidemiology at UC Davis, said: ‘Our results indicate that lead exposure in adulthood could contribute to worse cognitive performance within a few years.

‘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.’

Dr Conlon also found there were 7,507 lead-releasing facilities in the US in 2023. 

To reduce exposure, she said people living nearby 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 contaminated dust indoors. 

The above map shows populations served by drinking water with the highest levels of lead

A third study from Purdue University exposed human brain cells to lead in zero, 15 and 50 parts per billion, simulating the kind of lead exposure people might experience through contaminated water or air. The EPA’s action level for lead in drinking water is 15 parts per billion.

The researchers found neurons were more electrically active than those with no exposure, suggesting early signs of cognitive dysfunction. 

There was also an increase in amyloid and tau proteins. 

Dr Junkai Xie, lead study author and post-doctoral research associate in chemical engineering at Purdue University, said: ‘Our results show that lead exposure isn’t just a short-term concern; it may set the stage for cognitive problems decades later.’