The authors of this evidence review (Parker G 2006) hail from Australia’s Prince of Wales Hospital. They examined current evidence concerning the effect of dietary omega-3s on three common mood disorders: 1) depression (moderate to severe); 2) bipolar disorder (i.e., manic–depression); and 3) postpartum depression.

Rather than a formal statistical examination (i.e., meta-analysis), the Australian team sought only to detect general trends and identify data gaps. In addition to their generally positive conclusions, the authors call for studies designed to determine which omega-3 fatty acid—EPA or DHA—provides the greatest mood-enhancing benefit.

We’ve summarized their findings with regard to three mood disorders:

Depression: strong evidence of benefit

Several months before the current evidence review, the authors of another evidence review (Sontrop J 2005) had this to say about omega-3s and depression: “The relationship between ... [omega-3s] ... and depression is biologically plausible and is consistent across study designs, study groups, and diverse populations, which increases the likelihood of a causal relationship.”

Likewise, the authors of the current review (Parker G 2006) concluded that most evidence shows omega-3s can exert therapeutic effects in depressed people, and that higher seafood consumption and higher tissue levels of fish-borne omega-3s yield reduced rates of mood disorders.

While they identified one recent clinical study in which supplemental omega-3s produced no apparent positive effect on depression (Hakkarainen R 2004), they noted two likely reasons for this unusual failure, and proposed an intriguing explanation related to the successful outcome of a Finnish omega-3/depression study in women (Timonen M 2004):

• The subjects’ intake of EPA and DHA—the long-chain omega-3s used and found effective in almost all depression studies—was less than 0.5 grams (500 mg) per day (experts recommend getting at least 660 mg per day);
• Most of the omega-3 fatty acids consumed by the men in this negative study was alpha-linolenic acid; the form found in plants, only 5–15 percent of which gets converted into the long-chain “marine” forms essential to brain function (EPA and DHA).
• The negative findings of this male-only cohort study could be related to gender, since the results of a recent study in Finland showed that low fish consumption was only associated with depression in women. The Finns’ finding may mark the discovery of a distinction in the two gender’s degree of need for dietary omega-3s vis-à-vis depression-prevention. (The Australian evidence-reviewers noted that these results could indicate differences in the ways the two genders metabolize neurotransmitters and phospholipids.)

Bipolar Disorder (manic-depression): possibility of benefit; more study needed

The evidence with regard to this disorder—in which patients swing from depressed to hyperactive “manic” states—is less abundant and less clear than for “regular” depression. The results of two studies indicate that omega-3 supplements may help patients with bipolar disorder, but it remains to seen whether these possible benefits stem from some mood-stabilizing propensity of omega-3s or simply from their documented anti-depressant effect.

Postpartum Depression: mixed evidence; plausible rationale; more study needed

While the worldwide average rate of postpartum depression is 12.4 percent, national rates vary nearly 50-fold, from just 0.5 percent of mothers in affluent, seafood-loving Singapore to a horrifically high 24.5 percent of mothers in poverty-stricken South Africa.

We’ve reported the mixed results of small, “pilot” clinical trials that sought to determine the preventive effect of dietary omega-3s (see “New Study Supports Omega-3 Therapy in Post-Partum Depression”).

The authors of the current review note two things:

1. Studies in women and animals indicate that it is safe for them to take omega-3 supplements during pregnancy and the postpartum period;
2. The results of a cross-national analysis by leading clinician and omega-3 researcher Joe Hibbeln, M.D. (Hibbeln JR 2002) show that both higher seafood consumption and higher DHA content in the mothers’ breast milk predicted a lower risk of postpartum depression, and that higher reported seafood consumption predicted a higher DHA content in the mothers’ milk.

The Australian evidence-review team noted that omega-3 intake is likely to play a role in postpartum depression since, during the third trimester, the fetus accumulates an average of 67 mg of DHA per day, which is more than many women consume from fish or supplements (Innis SM 2003). For such women, transfer of DHA to the baby through the placenta and breast milk poses a risk of significant depletion of their own omega-3s during pregnancy and nursing, which could raise their risk of postpartum depression.

Study #3: Higher omega-3 tissue levels may reduce suicide attempts

Psychiatrist and omega-3 researcher Joe Hibbeln, M.D. is Chief of the Outpatient Clinic in the Laboratory of Clinical Studies at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland. We had the opportunity to hear him speak, and then speak with him at length, during last year’s Seafood & Health conference and at Dr. Andrew Weil’s Nutrition & Health conference in March of this year.

One of the studies published in the June issue of the American Journal of Psychiatry—which took place in Dr. Hibbeln’s clinic—compared the relationship between the tissue levels of omega-3s in seriously depressed patients and the rate at which they attempted suicide.

 
Dr. Hibbeln’s team recruited 33 adults seeking treatment for major depression who were free of any neurological or medical disease or substance dependence and were off antidepressant medications for at least 14 days prior to the start of the study.

His clinic has a reputation for suicide research and treatment of suicidal patients and attracts a high proportion of suicide attempters. Just over half of the subjects had a history of previous suicide attempt, and upon admission, most had failed recent depression treatment.

At the outset, the subjects’ blood levels of omega-3s (EPA and DHA) and the ratios of omega-6 to omega-3 fatty acids in their blood were recorded. The volunteers received inpatient (8 weeks) or outpatient (6 months) treatment from the research team, followed by community-based treatment.

Evaluations were performed at three, 12, and 24 months (by raters unaware of the subjects’ omega-3 status), with "time-to-subsequent-suicide-attempt" as the outcome against which the suicide-prevention power of higher ...

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