The study is an randomised controlled trial (RCT) to test whether supplementation of vitamins, minerals and n-3 fatty acids may reduce aggressive behavior in people with intellectual disabilities.

Rationale: The prevalence of aggression among people with an intellectual disability is high. Previous studies have demonstrated the potential of multivitamin-, mineral-, and n-3 fatty acids (n-3FA) supplementation to reduce antisocial behavior and aggression among schoolchildren and prisoners.

Objective: To test the hypothesis that multivitamin-, mineral-, and n-3 FA supplementation reduces aggression among adolescents and young adults with an intellectual disability.

Study design: Pragmatic, randomised, double blind, placebo controlled, multicentre intervention study.

Study population: People with an intellectual disability aged between 12-39 years, living at a care or treatment facility or having day care, who have shown aggressive behaviour.

Intervention: During 16 weeks, people in the active condition receive 4 supplements daily: 2 Bonusan Multi Vital Forte Actief (Multi vitamin and mineral) and 2 Bonusan Omega-3 Forte (n-3 fatty acids) while people in the placebo condition receive 4 placebo capsules.

Main study parameters/endpoints: The main study parameter is the number of aggressive incidents from baseline to endpoint (16 weeks post baseline), as measured using the Dutch version of the Modified Overt Aggression Scale (MOAS).

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Clients who wish to participate enter a 2-week run-in phase during which they take 4 placebo capsules daily. After positive evaluation of this phase clients are randomised to either the active or control condition. Participants will then start the daily use of 4 supplement capsules or 4 placebo capsules, which continues for 16 weeks. At baseline and endpoint 2 questionnaires will be administered: the Intellectual Disability Quality of Life (IDQOL-16) and the Dutch Healthy Diet Food Frequency Questionnaire (DHD-FFQ). Small hair and faeces samples will be collected at baseline and 16 weeks. The data collection will take less than an hour per client and will take place at the location where the client resides. Aggression incidents will be registered by staff members using the MOAS. Also a staff member will fill in the Social Dysfunction Aggression Scale (SDAS) at baseline and endpoint, measuring observed levels of aggression and social dysfunction. The risks of participating in this study are minimal. The use of the Bonusan Multi Vital Forte Actief, or similar supplements has not been associated with any significant health risks and side effects. Potential benefits of participating in this study is an increase in quality of life through improved nutritional status, as well as a reduction of aggressive incidents. As this is a pragmatic trial in which the main objective is to determine whether the use of supplements has the potential to reduce the number of aggressive incidents among adolescents and young adults with an intellectual disability, it is imperative to include these subjects.

Inclusion Criteria:

• intellectual disability
• living or day care in a health care organization
• age 12 till 39 years
• has a at least once a week an aggressive incident.

Exclusion Criteria:

• Pregnancy
• Breastfeeding
• people with Williams syndrome, hyperparathyroid or hemochromatosis.
• Current use of nutritional supplements and refusal to quit this use for the duration of the study.
• Failure to complete the two-week run-in phase.
• The use of the following medication: levothyroxine, methyldopa en levodopa

Placebo with the appearance as the dietary supplements