Exposure to common heavy metals has been linked to the prevalence of ADHD, according to a new study. It builds on existing research that has found that there’s a strong association between certain metals like lead and copper and increased cases of both ADHD and how serious the condition’s symptoms are.

Universittat Rovira i Virgili researchers investigated the possible association between urinary concentrations of 15 different heavy and essential metals and ADHD diagnosis and symptom severity in children (aged 6–15 years) from Barcelona (35.8%) and Tarragona (64.2%), Spain. Of the 190 kids studied, 124 had been diagnosed with ADHD and 66 had not.

The team focused on 15 metals: lead (Pb), arsenic (As), mercury (Hg), cadmium (Cd), chromium (Cr), copper (Cu), cobalt (Co), antimony (Sb), zinc (Zn), selenium (Se), magnesium (Mg), vanadium (V), manganese (Mn), nickel (Ni) and molybdenum (Mo).

The scientists collected 190 urine samples from children who had fasted for analysis, with collection guidelines lowering risk of external contamination from environmental factors. What they found was that children with the highest amount of lead, cadmium, copper and antimony present in their urine had a higher incidence of ADHD. What’s more, elevated copper and cadmium levels were linked to more severe inattention symptoms (something common in females with ADHD), and higher amounts of copper and antimony were associated with an increase in hyperactivity-impulsivity behaviors.

In the US, diagnosed ADHD cases among children and adolescents has risen from 6.1% in 1998 to more than 11% in 2022. However, much like autism statistics, there’s little evidence supporting the argument that more people are developing ADHD; instead, higher awareness of ADHD and better understanding of how it presents in females and adults has led to more people seeking medical intervention. Girls and women have, until recently, been underdiagnosed or misdiagnosed with other mood disorders that are symptoms of underlying ADHD.

This study, and earlier ones, linking exposure to certain heavy metals and an increased likelihood of ADHD is further complicated by the fact that the condition has high genetic heritability – somewhere between 70-80%. And this is also where it gets increasingly murky to pinpoint one root “cause,” because our environment can fundamentally change how our genes work – also known broadly as epigenetics – yet it’s complex, highly individualized and very difficult to study meaningfully.

In this study, it’s worth noting that the parents of the children involved were not assessed, so genetic ties were excluded. Also, among the 15 metals tested for, many – zinc, selenium, magnesium, manganese, cobalt and molybdenum – are essential minerals and beneficial at low levels. Lead, cadmium, mercury, arsenic and antimony are deemed toxic or heavy metals, while copper, chromium, nickel and vanadium are considered “dual-nature” and toxic at high levels.

The scientists noted that the metals found in testing could be attributed to common sources: Lead through old paint and plumbing, both lead and antimony from soil, dust and industrial emissions, cadmium from contaminated grains, spinach, peanuts and fertilizers, and copper from old pipes, cookware and water. Tarragona kids had higher levels of some substances like antimony and arsenic due to regional factors.

Vanadium, meanwhile, had a negative correlation with ADHD, in line with the little we know about this curious trace mineral. Recent research has looked at its potential benefits, in very low doses, for treatment of depression, schizophrenia and Alzheimer’s disease. While it’s an essential mineral for many organisms (mushrooms and rats, for example), it hasn’t yet been confirmed as one in human biology, and further research is needed to assess its safety and efficacy.

Nonetheless, there is a growing body of evidence that environmental factors, particularly exposure to lead, may be influencing ADHD and its symptoms. A 2024 metastudy of nearly 1,000 research papers found that there was a strong association between this metal and the prevalence of ADHD, though the biology underpinning this link is not fully understood.

Cadmium and lead – two metals implicated in this study – have frequently been singled out during the past decade, as has mercury, however, some research has cast doubt over this particular pollutant’s influence.

“Additionally, while this study adjusted for essential covariates (sex, age, BMI, SES, and diet quality), it could not adjust for other factors known to contribute to ADHD, including genetics, other environmental pollutants such as particulate matter, nitrogen dioxides, sulphur dioxide, pesticides, polycyclic aromatic hydrocarbon which are equally considered neurotoxic in nature,” the researchers noted. “Moreover, metals exposure was measured through urine, a non-traditional biomarker, and most metals have short biological life, that is, it only measures exposure to metals in the previous days or hours except for Cd, which indicates long-term exposure.”

In 2023, University of Notre Dame researchers demonstrated the mechanisms behind cadmium neurotoxicity, showing how the central and autonomic nervous systems are particularly vulnerable, and the metal can additionally interfere with neurotransmitter release. This area is, of course, very closely associated with the complex biochemical dysfunctioning seen in ADHD brains.

“The current exploratory study provides a comprehensive information on the potential associations of both heavy and essential metals exposure with neurodevelopmental disorder, in particular, ADHD in school-aged children,” the researchers concluded. “Remarkably it detected the exposure to heavy metals such as Pb, Cd, Cu, and Sb (Tarragona) potentially associated with the presence of ADHD. Furthermore, Cu and Sb being associated with higher hyperactivity-impulsivity symptoms and Cu, Cd and Pb with inattention severity. Whereas V unveiled a negative correlation with ADHD, suggesting a distinctive pattern of influence.”

It is important to point out that this study, as with previous research, does not prove any causation. And exposure to contaminants (lead, cadmium and copper) can be reduced through devices like water filters, plus avoiding hot tap water in cooking, because metals leach more rapidly with heat. Old urban soils have a higher risk of lead and arsenic contamination, so practicing good hygiene can avoid accidental ingestion. Cadmium exposure can be limited by more diverse dietary choices – for example, eating a variety of grains besides rice, oats, wheat and barley, which are the most prone to absorbing high levels of the mineral.

Other supplements – iron, zinc and calcium, omega-3 fatty acids, as well as vitamin C and E – can help block heavy metal absorption, support cognitive function and reduce oxidative stress from contaminants.

“These results highlight the complex interactions between exposure to heavy metals and neurodevelopmental disorders, providing important insights for research to further investigate the relation between these factors to minimize the effects of environmental influences on children’s health and wellbeing,” the researchers added.

The research was published in the Journal of Attention Disorders.

Source: Universittat Rovira i Virgili via Psypost