Doctors have found evidence to suggest that hyperactive children may benefit from taking zinc supplements.
Some parents give their children zinc supplements
Many parents whose children have attention deficit hyperactivity (ADHD)disorder give them extra zinc.
However, doctors are split on whether it actually works and few actually advocate it.
But a study in Iran on 44 children with the condition has found that those on zinc fared much better than those who were not given supplements.
Previous studies have shown that many children with ADHD have vitamin and mineral deficiencies.
The 44 children in this study were divided into two groups. Those in the first group were given 55mg of zinc each day for six weeks. Those in the second group were given a dummy pill.
All of the children were also given Ritalin, which is routinely prescribed to treat ADHD.
The researchers, who are based at Roozbeh Psychiatric Hospital in Tehran, said the behaviour of all of the children improved over the course of the study period.
However, they said those who had taken zinc had shown a more marked improvement.
The researchers suggested that zinc may play a role in regulating the production of dopamine in the brain.
This chemical is associated with feelings of pleasure and reward and has been linked to ADHD by other scientists.
The researchers said further study is needed to confirm the findings and examine if children with the condition should be given zinc.
"This study demonstrated that zinc as a supplementary medication might be beneficial in the treatment of children with ADHD.
"However, further investigations and different doses of zinc are required to replicate these findings in children with ADHD."
Professor Peter Hill of the Royal College of Psychiatrists said much more research is needed.
"I advised parents to give their children extra zinc in the 1970s. I don't do it now," he told BBC News Online.
"While it worked for some children, it did not work for others.
"There is a danger that children could be given too much zinc. I wouldn't advise parents to start giving their children zinc now."
The study is published in BMC Psychiatry.