In recent years, you’ve probably heard health experts extolling the potential cardiovascular benefits of eating more omega-3 fatty acids—fats found in fish and certain plant foods. Increasing evidence suggests that omega-3 fatty acids may also be beneficial for the prevention and treatment of certain mental disorders, particularly depression.
Omega-3’s: From the Land and the Seas
Omega-3 fatty acids, a type of polyunsaturated fat, are considered “good fats.” Omega-3 refers to their chemical structure. There are three types of omega-3 fatty acids: docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and alpha-linolenic acid (ALA).
The following foods contain omega-3 fatty acids:
Fatty fish, including:

Salmon
Mackerel
Tuna
Herring
Halibut
Plant foods, such as:
Ground flaxseed
Flaxseed oil
Canola oil
Soybean oil
Walnuts
Leafy greens
Tofu
Many health experts believe that omega-3 fatty acids may be crucial for brain function and that a deficiency could lead to or exacerbate mental illness in certain people.
Researchers “Fish” for Evidence
Depression
Depression has become increasingly prevalent in Western society. Some researchers believe that this may, in part, be due to major dietary changes that have occurred during the past century, which have resulted in a decreased consumption of omega-3 fatty acids. Several studies suggest that omega-3 fatty acids may be beneficial in the treatment of depression.
Omega-3 Levels in Diet and Red Blood Cell Membranes of Depressed Patients
A study published in the March 1998 issue of the Journal of Affective Disorders found low levels of omega-3 polyunsaturated fatty acids in the red blood cell (RBC) membranes of depressed patients but not in a well-matched healthy control group. The study also found that increasing severity of depression was related to decreasing RBC membrane levels of omega-3 fatty acids as well as decreasing dietary intake of omega-3 fatty acids.
Fish Consumption and Depression
In the April 1998 issue of The Lancet, Dr. Joseph Hibbeln, a researcher at the National Institute on Alcohol Abuse and Alcohol Consumption, reviewed data from nine countries and found a high incidence of depression in countries with low fish consumption. He cautioned that various economic, social, cultural and other factors could have influenced the results of the study. However, additional studies have found that high blood plasma concentrations of docosahexaenoic acid, an omega-3 fatty acid found in fish, have been linked to increased serotonin turnover and lower incidences of depression and suicide.
Fat-Restricting Diets and Depression
In the April 2000 issue of Nutrition Reviews, researchers reviewed a number of studies that suggest that there may be an association between extremely low-fat diets, low cholesterol levels, and an increase in the incidence of depression.
Included in the review was an observation by researchers at the University of Arizona that fat restriction and cholesterol-lowering drugs may change concentrations of polyunsaturated fatty acids in the tissues, including nerve tissue. Fat-restricting diets tend to lead to an increased intake of omega-6 polyunsaturated fatty acids and a relative decrease in the intake of omega-3 fatty acids. For certain people, these changes might increase the risk of depression.
The review included other large-scale studies that demonstrated a clear association between low blood levels of omega-3 fatty acids and an increased risk of depression, violence, and suicide.
The researchers concluded that omega-3 fatty acids are crucial for the proper functioning of the nervous system and that an extremely low-fat diet might lead to negative psychologic effects in certain people. They emphasized that dietary advice regarding cholesterol reduction, weight loss, and cancer prevention should stress the importance of an adequate intake of omega-3 fatty acids.
Bipolar Disorder
Bipolar disorder, or manic-depressive illness, is a brain disorder that causes extreme swings in mood, energy, and ability to function. The disorder is typically treated with mood stabilizing drugs such as lithium carbonate or valproate. However, these drugs are not always very effective and recurrence rates are high.
A Harvard study, published in the May 1999 issue of the Archives of General Psychiatry, found that omega-3 fatty acids were effective in the treatment of bipolar disorder when taken with a standard mood-stabilizing drug. The four-month, double-blind, placebo-controlled study compared omega-3 fatty acids from fish oil (9.6 grams per day) to a placebo (olive oil) in 30 people with bipolar disorder. The mental state of the participants was measured before and after the treatment, using the Clinical Global Impression Scale, Global Assessment Scale, Young Mania Rating Scale, and the Hamilton Rating Scale for Depression. The results were as follows:
Nine of the 14 people who received omega-3 fatty acids had a significant reduction in symptoms, while only 3 of 16 people who received the placebo showed a reduction in symptoms.
None of the participants taking the fish oil experienced a worsening of symptoms during the study, but nine of the participants taking the placebo experienced a worsening of their symptoms.
While most participants in the study were on mood stabilizers, eight received no concomitant medications. Of those eight, the four participants who received the fish oil completed the study without major episodes of mania or depression while only one of the participants taking the placebo did.
The results look promising for using fish oil, in conjunction with mood stabilizers, in the treatment of bipolar disorder. However, Andrew Stoll, MD, lead researcher and assistant professor of psychiatry at Harvard Medical School, cautions against using fish oil as a first line single treatment for bipolar disorder.
Schizophrenia
Schizophrenia is a serious mental illness often characterized by delusions, hallucinations, emotional blunting, and social withdrawal.
A study published in the 1996 issue of Lipids found that fish oil helped to reduce the severity of symptoms in a group of 24 patients with schizophrenia. Although none of the patients were clinically deficient in fatty acid intake before supplementation, their symptoms improved after being given 10 grams/day of concentrated fish oil for a six-week period.
Borderline Personality Disorder
Borderline personality disorder is a mental illness often characterized by intense fear of abandonment, mood swings, impulsive behavior, aggression, and self-injury. A recent study suggests that omega-3 fatty acids may help treat the symptoms of borderline personality disorder.
The study, published in the January 2003 issue of the American Journal of Psychiatry, consisted of 30 women who met the diagnostic criteria for borderline personality disorder based on the Structured Clinical Interview for DSM-IV Axis I disorders and the Revised Diagnostic Interview for Borderlines.
During the 8-week study period, 20 of the 30 subjects received two 500 mg capsules of an omega-3 fatty acid called E-EPA (ethyl-eicosapentaenoic acid). The remaining 10 participants received a placebo of two capsules daily containing mineral oil.
The researchers assessed levels of depression and aggression in the two groups at the beginning and ending of the study. At the end of the study, the researchers found that while depression and aggression levels dropped in the group taking the placebo, they had dropped even more in the group taking the omega-3 fatty acid. The researchers concluded that the omega-3 fatty acid used—E-EPA—may be a safe and effective form of treatment for women with moderately severe borderline personality disorder.
The Future of Omega-3’s and Mental Health
Additional research is needed to confirm the benefits of omega-3 fatty acids and mental health. However, some psychiatrists have started recommending that their patients with mood disorders eat foods high in omega-3 fatty acids or take supplements such as fish oil. Unfortunately at least one recent randomized trial and a separate Finnish study attempting to correlate omega-3 intake with depression suggested no relationship between intake (or treatment) and depression.
A Few Caveats
While most people can probably derive health benefits from eating more fish and omega-3 fatty acids, regardless of whether these improve depression, there are a few things to keep in mind:
Never use omega-3 fatty acids as a replacement for your psychiatric medication unless you have your doctor’s approval.
Fish oil supplements may cause side effects such as indigestion, gas, and fishy-smelling belches, however, this is less apt to be a problem if you start with a low dose and work your way up.
In general, fish oil supplements are safe. However, there is a slight possibility of increased bleeding. Therefore, consult your doctor before taking fish oil supplements, especially if you plan on having surgery.
If you take fish oil supplements, make sure they have been stripped of excess vitamins A and D, which could be toxic if taken in large amounts.
If you are pregnant or nursing, avoid shark, swordfish, king mackerel, tuna, and tilefish since they may be contaminated with mercury or other environmental pollutants.