Food and Behaviour Research

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Dutch prisoners enrolled in dietary supplement aggression study

by Eliot Beer

Violent offenders in the Netherlands will receive micronutrient and omega-3 supplements as part of an intervention to reduce aggressive behaviour among prisoners.


This study builds on previous research showing that nutritional supplementation can reduce antisocial behaviour. See:

Violent offenders in the Netherlands will receive micronutrient and omega-3 supplements as part of an intervention to reduce aggressive behaviour among prisoners.

Inmates with behavioural problems in five prisons and two youth institutions will receive the supplements including omega-3 fish oil, vitamins and minerals. While details, including the number of inmates to receive the supplements, are still being finalised, Ap Zaalberg, policy advisor at the Ministry of Security and Justice, said the estimated cost of the project was less than €1 per inmate per day.

Zaalberg is one of the authors of a 2010 study on the effect of providing dietary supplements to aggressive inmates in the Dutch prison system. That research, a partial replication of Bernard Gesch’s 2002 study , confirmed Gesch’s findings that giving inmates supplements cut violent behaviour by about a third.

Time for intervention

There have been two randomised controlled trials, one in England, and a few years ago we did a replication study in the Dutch prison system – both studies showed that vitamins, minerals and essential fatty acids had a positive effect on the behaviour of inmates. Since then there were fewer incidents,” said Zaalberg.

We’ve had two trials now – this is the science, and now it’s the practice. In the next few years we’re going to focus on implementing this intervention in practice – and after the implementation is successful, that’s when we will see if it’s effective. But at the moment, it’s an implementation problem,” he added.

Dutch justice ministry officials are now working with the prison system to finalise the programme’s details, including the timescale of the project and how the effects will be measured. Also to be finalised is the makeup of the supplements, but Zaalberg said it is likely to be close to the formula used in the Dutch study, with 100% RDA of vitamins and minerals, and “substantial” amounts of EPA and DHA, at either 800mg or 1,000mg.

According to Zaalberg, the long-term plan is to extend the intervention to more institutions, once the positive effects have been demonstrated: “When it’s successful, we can roll it out to more prisons. First we have to exercise with it.”

Low omega-3 link to violence

Following Gesch’s 2002 paper, there has been increasing interest in the efficacy of supplements to improve prisoners’ behaviour. An Australian study by Barbara Meyer and others , published in PLOS One in March this year, measured omega-3 levels in prisoners’ blood, and revealed a link between low omega-3 levels and aggressive behaviour.

[T]here is high variability in the levels of omega-3 index in inmates in a NSW Correctional Centre, with the majority having levels below 6% of total erythrocyte fatty acids. The omega-3 index correlates negatively with levels of aggressive behaviour, especially hostility and also with attention deficit disorder behaviour especially affect,” the paper’s authors wrote.

The significance of this link between diet and anti-social behaviour implies potential benefits for the correctional system and community safety at a population level. Supplementation with omega-3 and/or multi-vitamins and minerals is low cost and easy to administer compared to other forms of treatment for anti-social behaviour, and with further evidence from intervention trials could be a simple and effective contribution to treatment programs and the mental health status of offenders,” they added.