Exposure to heavy metal cadmium may double risk

• Cadmium, a toxic heavy metal found in polluted air, cigarette smoke, and food, was found to have a higher impact on cognitive ability in white people, a new studysuggests.
• In a study of more than 2,000 people, white participants with higher concentrations of cadmium in their urine had a doubled risk of cognitive impairment compared with those in the group with lower concentrations of cadmium.
• There was no such association for Black participants.
• The study only suggests an association of cadmium with reduced cognitive function in white people, not a direct causal relationship.

The highly toxic heavy metal cadmium, which finds its way into the body through cigarette smoking, breathing polluted air and food, was found to have a higher impact on cognitive ability in white people, a new study published in Neurologysuggests.

The study examined the urine of 2,172 people — more than half of which were female and nearly 40% of which were Black — with an average of 10 years for follow-up and found a “significant positive association” of cadmium in the urine of white participants with cognitive issues. Each year, the participants underwent thinking and memory tests, and over the 10-year average period, 195 people developed cognitive impairment.

Researchers found no association between cadmium levels and cognitive impairment in the overall study cohort. But white participants with higher concentrations of cadmium in their urine had a doubled risk of cognitive impairment compared with those in the group with lower concentrations of cadmium. There was no such association for Black participants.

Cadmium is a known carcinogen and can contribute to the development of dementia. It is released into the environment through industrial and agricultural activities. Its effect on the brain and central nervous system are widespread, with cadmium being able to disrupt calcium levels in the brain as well as activate signal pathways associated with inflammation and neural cell death.

The racial discrepancy in the odds of cognitive decline, according to the study authors, may be explained by the discrepancies in use of tobacco.

Black and white participants had similar levels of cadmium overall, but white people in the study had “substantially higher median smoking pack-years compared with Black participants,” the authors write. (In a pack year, a person smokes at least an average of one pack of cigarettes per day for a year.) They suggest that smoking provided the most exposure to cadmium for white participants.

Even in small amounts, cadmium is toxic for humans. It can penetrate the blood-brain barrier and stay in the brain, and it can accumulate over one’s lifetime.

David Merrill, MD, PhD, board certified geriatric psychiatrist at Providence Saint John’s Health Center in Santa Monica, CA, and Singleton Endowed Chair in Integrative Brain Health, who was not involved in the study, told Medical News Today that cadmium’s properties make it particularly insidious.

“Cadmium has a long half-life so can accumulate in the brain over a period of time and gradually cause problems with cognitive function,” Merrill said.

“Cadmium causes oxidative stress and interferes with key metabolic pathways. This leads to neuronal damage and even cell death. There can be reduced neurogenesis as well.”
— David Merrill, MD, PhD

MNT also spoke with Melanie Murphy Richter, MS, RDN, a registered dietitian nutritionist and the director of communications for the nutrition company Prolon, who was not involved in the study.

She told MNT that cadmium primarily enters the food supply through soil, and that socioeconomic factors play a role in what populations are exposed to higher levels of cadmium: exposure tends to be higher in industrialized regions or areas with heavy mining, smelting, or agricultural practices with cadmium-containing fertilizers.

Countries with high levels of air pollution and unregulated industrial emissions can have higher cadmium levels in the environment.

“In the U.S., exposure is often higher in industrialized areas or regions with a history of heavy metal contamination, such as parts of the Midwest (due to historical mining activities) or areas near industrial plants. Socioeconomic factors also play a role—people in lower-income areas, which may have higher pollution levels, might face greater exposure. Additionally, smoking rates vary by region and demographic, which can increase exposure in specific communities,” Richter said.

“Industrial processes, mining activities, and the use of phosphate fertilizers, which often contain cadmium, contaminate soil over time. Plants, particularly certain crops like rice, wheat, and leafy greens, can absorb cadmium from this contaminated soil. As these crops are consumed, cadmium makes its way into the human food chain. Fish and shellfish may also contain cadmium if they are caught in polluted waters.”
— Melanie Murphy Richter, MS, RDN

The study authors note that further studies are needed to get a more solid cause-and-effect idea of cadmium on different populations. They cited the need for “repeatedly measured Cd exposure, larger sample sizes, and longer duration” in future research to be able to form explanations for the racial discrepancy.

Merrill said that higher rates of dementia have been associated with more cadmium in those populations’ environments but cautioned against seeing a direct link.

“Regions in the U.S. and abroad with higher environmental cadmium levels have shown higher incidence of dementia, but more research is needed to establish a direct causal link,” he said.

Richter agreed that more data is needed to establish any stronger connection between cadmium and dementia.

“While the study highlights the potential link between cadmium and cognitive decline, it does not supply enough data, yet, to trace cadmium exposure directly to dementia rates in specific communities,” she said.

“However, it is possible that communities with higher cadmium exposure—such as those near industrial areas or with higher smoking rates—might have increased risks of cognitive problems over time. More research would be needed to establish a clear connection between cadmium exposure and dementia rates in those regions,” she added.