Omega-3 fatty acids*, especially EPA, have been linked to various clinical and behavioral conditions involving mental function. These include depression, bipolar disorder, schizophrenia, violence, aggression, and attention deficit hyperactivity disorder. These fatty acids are also associated with certain neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases. A common feature of these disorders is low levels of the marine or fish oil omega-3s, EPA and DHA. Sometimes the omega-6 fatty acid arachidonic acid is reduced too.
Low levels of omega-3s have not been shown to cause any of these disorders, but they appear to significantly increase the chance of developing them. Other factors are often involved, such as family history and environmental influences. All the same, there is a plausible basis and growing evidence for the involvement of marine omega-3s in brain function in these conditions.
Depression is least common in countries where people eat the most fish, such as Japan, Iceland, and Korea, while countries with low fish consumption have the highest rates. They includes the U.S., Canada, and West Germany. People with depression often have low levels of EPA and DHA in their tissues compared with healthy people, but it is not clear what this means.
Several studies have reported positive outcomes in depressed patients who took EPA along with their usual medication. Low doses of EPA (1 to 2 grams/day) were more effective than high doses, and EPA appears to be more effective than DHA. However, these encouraging findings must consider that some studies found no benefits with EPA. Moreover, almost all studies have been carried out with small numbers of patients. That means we still need firmer results from larger studies under more controlled conditions. In its favor, however, EPA appears to work at low doses and be without adverse effects.
Schizophrenia: Less common than depression, schizophrenia is a crippling mental illness that affects about 1% of the US population. There are several neurologic and biochemical alterations in this condition, including reduced cell membrane levels of arachidonic acid and DHA. Occurrence of schizophrenia in different countries does not appear to be linked to seafood consumption. Nearly all patients are treated with medications, so studies of supplementation with omega-3s include drug treatment too. Some medications may reduce cell fatty acids, so it is difficult to distinguish the effects of more than one treatment.
The majority of studies, but not all, reported improved assessment scores in schizophrenic patients taking medication and low doses of EPA. In comparison, patients taking only medications showed no improvements. Most studies reporting benefits used 1 to 3 grams of EPA a day. A few trials with higher doses have found no benefits. On balance, the available studies suggest improved assessments when 1 to 2 grams of EPA/day are consumed. However, as is often the case, shortcomings in the data prevent firm conclusions.
Bipolar disorder: Bipolar disorder – sometimes called manic-depressive illness – is characterized by unusual mood swings from overly high to hopeless and back again. It, too, can be disabling, but drug therapies have brought substantial improvements. Like depression, its occurrence is significantly lower in countries with robust seafood consumption and higher where people eat fish infrequently.
Aggression and Violence:The extremes of depression and hostility are violence, homicide, and suicide. Here, too, observations in different regions of the world have noted significantly higher rates of homicide and suicide where fish consumption is low compared with places where fish intake is high. Male violent offenders have lower DHA in their red blood cells than non-violent men. A limited number of studies reported significantly lower marine omega-3s in red cells in people with hostile or aggressive behaviors compared with their more amiable counterparts. But caution: these observations are only suggestive and do not establish that omega-3s are involved in such behaviors. Other nutrient shortfalls, such as folic acid, have also been detected in aggressive people. What makes these observations tempting is that they go hand in hand with related behaviors where marine omega-3s have had some beneficial effects. This means they are worth looking into more seriously. Time will tell.
*Words in blue are described in the glossary.