The effects of ADHD on individual children differ, but symptoms include inattention, hyperactivity and impulsiveness. Stimulants are the most common treatment prescribed, but some patients respond poorly to stimulants or are unable to tolerate them. Also recent findings that vitamin and mineral deficiencies correlate with ADHD suggest that dietary supplements could also play a role in disease management.
Researchers from Iran carried out a controlled trial to assess the benefits of prescribing supplementary zinc alongside the more conventional methylphenidate treatment. They found that children taking additional zinc sulphate on a daily basis improved faster than those taking a placebo.
"The efficacy of zinc sulphate to increase the rate of improvement in children, seems to support the role of zinc deficiency in the pathogenesis of ADHD," say the authors of the study, published in this week's issue of BMC Psychiatry (4:8).
Research published earlier this year by a team at Karadeniz Technical University in Trabzon, Turkey found that zinc sulphate significantly reduced symptoms of hyperactivity, impulsivity and impaired socialization in patients with ADHD, particularly older children and those with low zinc and fatty acid levels.
But the new study is thought to be the first controlled clinical trial looking at the effects of zinc alongside conventional medication.
The study comprised 44 children who were diagnosed as suffering from ADHD at Roozbeh Psychiatric Hospital, Tehran. Prior to the trial none of these patients had taken any medication for their condition. For the six weeks of the trial, half the children took zinc sulphate (55mg/day) in addition to the conventional treatment; the other half took a placebo.
A child psychiatrist assessed the children's condition fortnightly. The behaviour of both groups of children improved over the course of the trial, but the children taking the zinc supplements showed a more marked improvement in their condition after six weeks, compared with those taking the placebo.
Although the children taking zinc sulphate were three times more likely to report that they were suffering from nausea, the frequency of other side effects did not differ between the two study groups. However, almost all of the children taking supplementary zinc complained about the metallic taste of the tablets.
Zinc supplements may exert their positive effects by helping to regulate the function of the neurotransmitter dopamine, suggested the researchers. Dopamine signalling, which has been implicated in causing symptoms of ADHD, is believed to play an important role in the feelings of pleasure and reward. The hormone melatonin, made in the body but requiring zinc for its production, regulates dopamine and has been shown to help regulate the sleep cycle of children with ADHD.
Further research on a larger group of subjects and with different dosages is needed to confirm the positive effects of the supplements on children with ADHD, noted the researchers.