People felt less aggression after just 6 weeks of Omega-3 – RCT Dec 2017

Omega-3 supplements reduce self-reported physical aggression in healthy adults

Psychiatry Research December 2017, DOI: 10.1016/j.psychres.2017.12.038

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Laurent Beguea’[email protected] , Ap Zaalbergb, Rebecca Shanklanda, Aaron Dukea, Julie Jacqueta,
Perla Kalimanc, Lucie Penneld, Marc Chanovee, Philippe Arversa, Brad J. Bushmanf
a LIP/PC2S, University Grenoble Alpes, Grenoble, France.
b Ministry of Security and Justice, Crime, Law Enforcement and Sanctions Research Division (CRS), The Hague, The Netherlands.
c Center for Mind and Brain, University of California, Davis, United States.
d University Hospital, University Grenoble Alpes, Grenoble, France.
e MSH Alpes, CNRS/University Grenoble Alpes, Grenoble, France.
f School of Communication and Department of Psychology, The Ohio State University, Columbus, Ohio, United States.

There is emerging evidence that Omega-3 polyunsaturated fatty acids (PUFA) supplements can decrease aggression. However, experimental studies with adults from non-specific populations are scarce. We hypothesized that Omega-3 supplements would decrease self-reported aggression among non-clinical participants. In a doubleblind randomized trial, two groups of participants (N = 194) aged 18-45 from the general population followed a 6-weeks treatment with 638 mg docosahexaenoic acid (DHA) and 772 mg eicosapentaenoic acid (EPA) per day or the equivalent quantity of copra oil (placebo).
Self-reported aggressiveness was measured at baseline and after the 6-week treatment period. Findings showed that Omega-3 supplements significantly decreased self-reported aggressiveness at the end of the 6-week period (d = 0.31).

In conclusion, this experiment indicates that Omega-3 administration has beneficial effects in reducing aggression among the general population.

Discussion

As predicted, this experiment showed that omega-3 supplements decreased self-reported aggression levels among non-clinical, adult participants. The effect size d = 0.31 exceeded the benchmark value of d = 0.25, which is reserved for treatments labeled as significant, important, notable, and consequential (Promising Practices Network (PPN), 2014). Thus, the reduction in aggression levels caused by taking omega- 3 supplements for 6 weeks was not trivial.
This experiment had five primary strengths.

• First, the sample size was larger than in similar studies. However sample size estimates (see Cohen, 1988) suggested that to detect an effect of d = 0.31, with the power set at 0.80, a much larger sample would be necessary (approximately 335). The power of the present study was estimated at 0.57. *Second, it used a sample of participants from the general population rather than a clinical sample.
• Third, it isolated the effects of omega-3 fatty acids from other nutritional supplements that might influence aggressiveness.
• Fourth, the double-blind procedure was successful. An inherent problem in the study of fatty acid is keeping participants blind to conditions due to the fishy aftertaste of fish oil. For example, in one study 49% of participants guessed they were taking fish oil at the beginning of the study, which rose to 75% at the end of the study (Zaalberg, 2010; also see Giles et al., 2015). In order to keep participants blind to their condition, all participants were told that the pills could have a fishy aftertaste.
• Fifth, it used a valid and reliable objective measure of aggressiveness.

This experiment also had at least four weaknesses.

• First, we did not measure long-term patterns of dietary intake, so the intake estimates might be inaccurate.
• Second, we did not have access to biological samples from the participants that could be used to determine the cellular levels of omega-3 fatty acids. However, most omega-3 studies share this limitation.
• Third, we only studied short-term effects of omega-3 after taking supplements for only 6 weeks. It would be important for both clinical and social purposes to investigate the longterm effects of omega-3 supplements on aggressiveness. However, it is worth noting that a meta-analysis found no relationship between the length of omega-3 supplementation and ADHD problems (Cooper et al., 2016).
• Fourth, the outcome measure was a self-report measure of aggression, which represents a weaker measure than a behavioral measure of aggression (e.g., Gesch et al., 2002). It should also be noted that the levels of aggressiveness in the study population were very low at baseline.

We offer three suggestions for future research.

• First, we recommend taking blood levels of omega-3 fatty acids in future studies. Blood samples might be better predictors of study outcomes. Blood samples also provide the opportunity to test hypotheses about genetic determinants of responding to omega-3 fatty acids, as has for instance been suggested for the ApoE4 allele carriers (van de Rest et al., 2008; Plourde et al., 2009). Blood samples also provide the opportunity to test possible interactions with other nutrients.
• Second, some omega-3 fatty acid studies suggest that effects in non-aggressive study populations are more pronounced under stressful conditions (Hamazaki et al., 1996). Future experiments can directly test this hypothesis by also manipulating the level of stress.
• Third, because levels of physical aggressiveness turned out to be very low in our study population, it also might be useful to measure other aspects of aggressiveness, such as verbal aggressiveness.

In conclusion, this experiment suggests that omega-3 administration may reduce physical aggression in the general population. This is an important positive effect of omega-3 supplements, in addition to their many other positive benefits.
Funding: This research was funded by Ministry of Health, France.

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