Two new studies yielded opposite findings on a key question: Do omega-3s from fish help deter depression?
A small clinical trial in 46 clinically depressed Italian women found mood and well-being benefits in the group taking fish oil for two months.
In contrast, a new analysis from Harvard found no link between higher estimated omega-3 fish-fat intake and risk of depression among almost 55,000 American nurses.
The Harvard study did detect mood-protection from diets high in omega-3s from plant foods … but those risk reductions weren't seen among nurses whose high omega-6 fat intakes resembled most Americans' excessive omega-6 consumption.
For more on that, see our sidebar, “Fishy omega-3s show mood benefits in most studies”.
Clinical study affirms mood benefits in elderly
The results of a small but well-designed Italian clinical trial support the findings of the APA and NIH-funded evidence reviews (Rondanelli M et al. 2011).
Researchers from the University of Pavia recruited 46 clinically depressed senior women – from 66 to 95 years of age – at a nursing home, for a randomized, double-blind, placebo-controlled trial lasting two months.
The women were randomly assigned to receive either omega-3 fish oil supplements – containing 2.5 grams of omega-3s (1.67 grams EPA + 0.83 grams DHA) – or placebo capsules.
The women in the omega-3 group showed a significant average reduction in depression symptoms, as measured by the Geriatric Depression Scale test.
This mood benefit corresponded to higher levels of omega-3 fatty acids in the women's red blood cells.
In addition, when the women were asked to evaluate their own quality of life, those in the omega-3 group reported improvements.
Fishy omega-3s show mood benefits in most studies
In 2006 an expert panel of the American Psychiatric Association (APA) reviewed the available evidence on omega-3 fatty acids and mood disorders.
The APA's expert committee concluded that in general, omega-3s from fish (EPA and DHA) reduce risks of depression, bipolar disorder (manic-depression), and related disorders, and hold some therapeutic promise.
As they wrote, “EPA and DHA appear to have negligible risks and some potential benefit in major depressive disorder and bipolar disorder …” (see “Top Psych Panel Says Omega-3s Deter Depression, Bipolar Disorder”).
Last year, those conclusions were echoed by the results of a “meta-analysis” of 15 randomized, double-blind, placebo-controlled studies funded by the U.S. National Institutes of Health:
“… patients taking omega-3 with either EPA or a combination of EPA and DHA experienced clear antidepressant benefits.” (ACN 2010)
(See “Mood Benefits of Omega-3s Affirmed”.)
And as lead author John M. Davis, M.D., said, “Our analysis clarifies the precise type of omega-3 fatty acid [EPA, much more than DHA] that is effective for people with depression and explains why previous findings have been contradictory”. (ACN 2010)
(For this trial “quality of life” was defined as a perceived satisfaction with regard to physical and mood health, as well as overall well-being.)
The Italian scientists claimed that in this respect, their trial adds new information:
“This [improved quality of life] observation has never been achieved before and it appears of great value from the clinical point of view, due to the importance of these aspects in the elderly population.” (Rondanelli M et al. 2011)
Harvard study found no depression-risk drop with omega-3s from fish:
Plant-derived omega-3s worked modestly, but only when omega-6 intake was low
Last month, researchers from Harvard University reported contrary findings from their analysis of diet-health data from women participating in the famed Nurses' Health Study.
As the Boston-based team wrote, “… the results of this large longitudinal study do not support a protective effect of long-chain n-3 [omega-3] fatty acids or fish intake on the risk of depression.”
(A longitudinal study is one in which people are followed over time, to look for links between their diets and lifestyles and changes in their health status.)
Of course, as in most epidemiological studies, the Harvard researchers had to rely on participants' reported diets to calculate estimated omega-3 intakes.
In contrast, the Italian study described above – like other positive clinical trials testing omega-3s for depression – measured volunteers' actual omega-3 blood levels … and higher levels correlated to higher mood-test scores.
The Harvard study entailed a comparison of the diets and mood health of 54,632 female nurses aged 50 to 77, who were free from depression symptoms at the beginning of the 10 year study.
Over the next decade, about five percent of the women developed clinical depression … and their risk was the same regardless of how much omega-3 DHA and EPA the women were estimated to have consumed from eating fish.
Somewhat surprisingly, the analysis suggests that the plant-derived omega-3 called alpha-linolenic acid (ALA) may play a positive role in mood support.
Omega-3 ALA occurs in leafy greens like spinach and collards, but is much more concentrated in flaxseed, walnuts, and canola oil.
(The body converts ALA, very inefficiently, into EPA and DHA … the only omega-3s essential to human life, which are found only in seafood or supplemental omega-3 oils from fish, krill, and other marine creatures.)
Higher omega-3 ALA intakes were associated with a reduced risk of clinical depression … but only among women who reported the lowest omega-6 LA intakes. (Lucas M et al. 2011)
For every estimated increase of one-half gram (500mg) in daily intake of omega-3 ALA, there was an 18 percent reduction in the risk of depression.
It seems very significant that no risk reduction was seen in women with the highest reported intakes of omega-6 LA (linoleic acid)… which competes with omega-3 ALA for conversion into the long-chain omega-3s (EPA and DHA) the body needs for basic brain functions.
Mood expert takes negative findings with a grain of salt
Psychiatrist Teodore Postolache, M.D., directs the mood and anxiety program at the University of Maryland School of Medicine in Baltimore.
In an interview with Reuters Health, Dr. Postolache said he was not remotely ready to give up on fish oil:
“There are inherent limitations on studies about depression, including determining with certainty what exactly depression is for patients.” (Horowitz J 2011)
For example, nurses know more about health and diet than most, so, as he said, “If groups who may have underlying deficits in fish oil were studied, like lower socioeconomic groups, we might have seen a more powerful effect of the omega-3s in preventing depression.” (Horowitz J 2011)
Dr. Postolache also noted that the study excluded women who'd had depression in the past, although, as he said, this group is one of “… the most important targets for intervention because they are at high risk for a repeat episode.” (Horowitz J 2011)
He called for more research on animals and in broader swaths of the population.
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