A Dutch study aims to get a grip on violence in prisons by prescribing vitamins and minerals for inmates with anger management issues, justice officials said this week.

Starting early next year prisoners at seven institutions who show violent tendencies will receive added vitamins, minerals and fish oil, the justice ministry said.

"Two previous experiments have shown that aggressive prisoners who receive food supplements show less aggression than those who do not," said Ap Zaalberg, a researcher at the ministry.

A British study carried out in the late 1990s showed violent incidents in prison dropping by at least a quarter after supplements were added to prison food, Zaalberg told AFP.

A similar study of 200 prisoners in the Netherlands in 2006-2007 showed a drop of 34 percent in incidents, Dutch daily De Volkskrant recently reported.

"We are now checking whether the addition of food supplements can be introduced in prisons as common practice, including as a form of treatment for aggression," said Zaalberg.

Boys and men at five prisons and two youth detention centers, aged from 12 to "quite old", would take part in the study, he said, adding "the aspect they'll have in common are anger issues."

Aggression is a feature of prison life in many countries.

Roughly a quarter of prison workers in the Netherlands experience threatening behavior by inmates, De Volkskrant reported.

Food scientists at Wageningen University near Utrecht however said although supplements could have a positive effect, Dutch prisons should instead focus on improving prison cooking.

A positive effect on prisoners "really starts in the kitchen," nutritional scientist Frans Kok told NOS public broadcaster.