Several studies suggest that consumption of oily fish or omega-3 supplements can reduce aggressive behaviour.
A study in Japan that was published in 1996 showed students consuming fish oil had reduced tendencies to become aggressive under stress, in comparison with non-fish oil consumers. More recently, in 2004, information emerged from an observational study begun in New York in the 1990s. The information on hostility among 3,581 urban white and black young adults again showed a link with fish consumption. Low fish consumption correlated with the higher levels of hostility.
Similarly, in the UK, dietary supplements with vitamins and fish oils were given to young prisoners in a maximum security institution. The prisoners were aged 18–21 and typically serving long sentences for serious offences. A group of 231 was divided into those given supplements (1260mg linoleic acid, 80mg gamma linoleic acid, 80mg EPA and 44mg DHA) and others receiving placebo for 142 days. Participants receiving the supplements became 26% less likely to be reported for antisocial behaviour than the control group. In a separate study reported in 2006, omega-3 supplements helped 28 young boys, aged 10 to 16, with severe behavioural problems to control their anger. In the six-month trial, serious anger outbursts were reduced by more than 60% compared with the previous six months.
In Boston, women suffering borderline personality disorder were recruited to an eight-week trial using supplementation with ethyl EPA or placebo. Those taking ethyl-EPA experienced a significant decrease in aggression as well as diminished symptoms of depression.