Omega 3 Fatty Acid Supplements and Autism Ranking:

There are a number of limitations to all of the research studies published to date. For example

Four of the studies used single-case designs, that is, they did not have a control group of participants who did not receive the omega-3.

Five of the group studies and two of the single case designs included fewer than 30 participants. For example, the randomised controlled study by Amminger et al (2007) only had 13 participants.
Most of the studies were restricted to specific groups of participants. For example one study (Voigt et al, 2014) looked only at children aged two to five diagnosed with autistic disorder.
One of the studies (Yui et al, 2012) included participants from a wide age-range (six to 28 years old) with a range of diagnoses (Asperger syndrome and autistic disorder).
One of the studies (Johnson et al, 2009) examined 75 participants with ADHD, only 23 of whom were also autistic.
One of the studies (Boone et al, 2017) examined infants “at risk” of autism so could not verify the diagnosis of autism using established diagnostic tools like the ADOS or ADI-R.

Some of the studies examined supplements containing a range of omega-3 fatty acids while others only examined supplements containing one type of omega-3 acid, making it difficult to know if any effects were caused by one or more specific acids.
One of the studies examined a supplement which combined omega-3 with omega-6 and one of the studies examined a supplement which combined omega-3 with omega-6 and omega-9. This makes it difficult to know if any effects were caused by the omega-3, the omega-6, the omega-9 or all of them.
In one of the studies (Bent et al, 2014) only 69% of the doses of omega-3 were actually taken by the experimental group, which is a very poor adherence rate.
Many of the studies ran for relatively short periods of time (six to eight weeks).
One of the crossover studies (Parellada et al, 2017) had a relatively brief wash out period (two weeks) between the omega-3 and the placebo.

One of the controlled studies (Meguid et al, 2008) compared a group of autistic participants who received omega-3 with a group of non-autistic participants who also received omega-3, rather than with a group of autistic participants who did not receive the omega-3.
One of the studies (Amminger et al, 2007) had much higher scores for hyperactivity and repetitive behaviours in the experimental group than the control group at the start of the treatment. This means that the decreases in hyperactivity in the experimental group reported at the end of the study may have been due to a statistical effect called “regression to the mean” rather than to a real treatment effect.

Some of the studies (such as Amminger et al, 2007) did not provide any data on the fatty acid levels of the participants at the beginning or end of the intervention.
Some of the studies (such as Meguid et al, 2008) did not provide any data on any adverse or harmful effects.
In one of the studies (Politi et al, 2008) a single outcome measure that is not widely known was used (the Rossago Behavioral Checklist).
One of the studies (Meiri et al, 2009) provided data from one of the outcome measures (ATEC) but did not provide any data from the other outcome measures (CARS, CGI, CPRS).
In one of the studies (Bent et al, 2014) the reported outcomes were based on parent and teacher observation but there were was no direct clinical observation by the therapists.
Some of the studies (such as Johnson C. et al, 2010) did not provide any information on the effect size of the intervention.
Some of the studies (such as Meiri et al, 2009 did not provide any kind of statistical analysis of the outcomes (such as statistical significance or confidence intervals).
Some of the studies (such as Bent et al, 2011) reported limited benefits (such as improvements in hyperactivity) but these benefits did not reach statistically significant levels.
Most of the studies did not undertaken any kind of follow up to identify if omega-3 had any beneficial or harmful effects in the medium to long term (six months or longer).

Very few of the studies appeared to involve autistic people and parents and carers in the design, development and evaluation of those studies.

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