Metals and other elements can be present in food either naturally, as a result of human activities (such as farming, industry or car exhausts), from contamination during manufacture/processing and storage, or by direct addition.
It has long been known that excessive amounts of any metal could be potentially dangerous, but there is now also strong evidence that some trace elements can contribute to aggressive or anti-social behaviour, said Neil Ward, professor of chemistry at the UK’s University of Surrey.
“Many of the mechanisms are as yet unknown and more case studies are required, but it is clear that elimination produces positive improvements,” said Professor Ward at a Food and Behaviour conference held in Brighton, UK, last week.
Some metals and other elements (such as copper, manganese and zinc) can act as nutrients and are essential for health, while others (such as arsenic, cadmium, lead and mercury) have no known beneficial health effects.
Nutrient depletion
Those elements that have no nutritional benefits could not only be toxic to the system, but they could impede absorption of essential nutrients in the body, which is particularly problematic in children, explained Ward.
For example, lead has been linked to anti-social behaviour, partly because it contributes to nutrient depletion.
“Lead acts as an anti-nutrient, hindering the utilisation of magnesium, zinc and vitamin B1. High lead levels have been linked to a reduction in IQ, negative classroom behaviour ratings by teachers, juvenile delinquency and increased violent behaviour,” he said, citing studies by Needleman et al., which appeared in the New England journal of Medicine, JAMA and Neurotoxic Teratology in 1990, 1996 and 2002 respectively.
Ward, who has studied the relation of trace elements to human disorders for over 25 years, said aluminium has also been linked to anti-social behaviour as it competes for the binding sites of biochemical receptors of other metal ions, such as iron and zinc. For the same reason, suboptimal dietary intake of zinc or iron could explain the uptake of aluminium, he said. References included studies by Moon and Marlow, Wenk and Stemmer, and Birchell and Chappell, which appeared in Biol Trace Elem Res (1986), Brain Res (1983) and the Lancet (1988) respectively.
Missing zinc
Ward also highlighted findings from one of his own studies, conducted in 1995, which examined the heavy metal status of incarcerated young offenders compared to control individuals.
The double-blind case control study used scalp hair and blood serum tests to determine the levels of zinc, lead, cadmium and aluminium in the two groups. Levels of lead, cadmium and aluminium were found to be significantly higher in the young offenders group, whereas zinc levels were lower.
Zinc deficiency is also thought to occur as a result of ingestion of certain food colours, and has been linked to hyperactive behaviour or ADHD in children, said Ward.
“The mode of action is not known, but azo dyes have been linked to behavioural changes in children. These colours could be acting as chelating agents, which bind available blood zinc and create a deficiency. The elimination of azo dye beverages and sweets can have a dramatic effect on some HA or ADHD children,” he said.
Food and Behaviour
Professor Ward was addressing an audience of medical professionals, teachers, healthcare and social workers, and food industry executives at a conference organised by the charity Food and Behaviour Research (FAB).
FAB aims to provide research-based information on how nutrition and diet can affect behaviour, learning and mood. For more information, click here.