Findings are balanced by prior positive research; evidence remains mixed on the role of fish-borne omega-3s in reducing the risk of mental illnesses
by Craig Weatherby
Bucking the general trend, a population study from Finland found no signs that long-chain omega-3s (EPA and DHA) can deter mental problems.
Fish is the only abundant food source of omega-3 EPA and DHA, and fatty fish like salmon, tuna, mackerel, sablefish, herring, and sardines provide the most per ounce.
We see three reasons why the Finnish findings should be taken with a grain of salt.
First, this negative finding is balanced by a substantial amount of epidemiological and lab evidence suggesting that omega-3s exert a positive influence on mental health… especially when it comes to dementia (e.g., Alzheimer’s disease) and depression.
And there is some preliminary clinical evidence that omega-3s may reduce the risk or severity of mental problems other than depression and dementia.
For example, we reported earlier this month on the positive results of a small, pilot clinical trial that tested omega-3 fish oil in mentally unstable adolescents at high risk for developing full-blown psychosis (see “Omega-3s Curb Psychosis in Clinical Trial”).
Second, the Finnish team did not consider the volunteers’ intake of omega-6 fatty acids, excessive consumption of which is associated with greater risk of mental problems (Hibbeln JR 2007).
Omega-6 fats also compete with dietary omega-3s for absorption into our cell membranes, and the standard American diet is grossly overloaded with omega-6 fats relative to omega-3s.
For more on that topic, see “Report Finds Americans Need More Omega-3s and Less Omega-6s”, and search our newsletter archive for “omega-6”.
Finally, epidemiological studies, such as this one, only show associations between foods or nutrients and health conditions. They cannot prove whether a food factor does or doesn’t affect risk of a disease (Only well-designed clinical trials can do that).
Details of the Finnish mental health study
Researchers at Finland’s National Institute for Health and Welfare (THL) analyzed the health records of 12,108 men and women (Suominen-Taipale AL et al. 2010).
The records included the results of blood tests (including omega-3 blood levels), as well as the participants’ diets and mental health status, which were determined using standard questionnaires.
As you might expect in a Scandinavian country, many of the participants reported eating fish frequently.
But the participants’ self-reported mental health status could not be linked to their fish intake, omega-3 blood levels, or reported use of omega-3 fish oil supplements.
In other words, the volunteers’ omega-3 intakes
—as determined by diet questionnaires and blood tests
—bore no significant statistical relationship to their self-reported mental health status.
More surprisingly, mental distress was reported more frequently by men whose blood contained higher levels of omega-3 DHA… the primary and most essential fatty acid found in brain cell membranes.
Frankly, this last finding is so inexplicable as to give us pause about the accuracy of the authors’ analysis.
They wrote that they took possible “confounding” factors into account (i.e., alcohol, smoking, and physical activity), but they did not consider omega-6 intake… a pretty large oversight that makes us wonder whether they accounted properly for the effects of other foods or behaviors.
Clinical trials needed to clarify mixed signals on omega-3s for mental health
Most people have the impression that omega-3s are proven to prevent or alleviate depression.
However, for the moment, “proven” is too strong a word to use in that regard.
It’s true that most of the available evidence—which consists largely of epidemiological studies and small “pilot” clinical trials—lends credence to the idea that omega-3s support mood health.
This was the conclusion of an expert panel assembled by the American Psychiatric Association (APA):
“[Omega-3] EPA and DHA appear to have negligible risks and some potential benefit in major depressive disorder and bipolar disorder, but results remain inconclusive in most areas of interest in psychiatry” (Freeman MP et al. 2006).
To learn more about their report, see “Top Psych Panel Says Omega-3s Deter Depression, Bipolar Disorder”.
The APA panel’s conclusions were similar to ones arrived at by two other evidence reviews published during the past four years:
“While it is not currently possible to recommend omega-3 PUFA as either… [the sole or supporting]… therapy in any mental illness, the available evidence is strong enough to justify continued study, especially with regard to attentional, anxiety and mood disorders (Ross BM et al. 2007).
“The relationship between fatty acid status and mental disorders is confirmed by [the fact that there are] reduced levels of [long-chain omega-3] fatty acids in [the red blood cell] membranes of patients with central nervous system disorders. Nevertheless, there are very little data supporting the use of fish oil in those patients” (Assisi A et al. 2006).
Conclusions like these reflect a woeful lack of clinical evidence, rather than any actual certainty about the role of omega-3s in mental health.
Only large, well-controlled clinical trials can prove that a proposed preventive or therapeutic agent actually works, to what extent it works, and for which specific condition(s).
Sadly, while big pharmaceutical companies can afford to pour billions into developing what are often marginally effective new or “improved” drugs, very little public money is available to clinically test promising but non-patentable (hence unprofitable) food factors… such as omega-3 fatty acids.
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