More on Omega-3 Fatty Acids and Psychiatric Disorders
By Jerry Cott, PhD
It has been suggested that depletion of omega-3 polyunsaturated fatty acids (PUFAs), particularly docosahexaenoic acid (DHA), impairs membrane function and may be of etiological importance in depression, aggression, schizophrenia, and other mental and neurological disorders.1-4
The American diet is low in omega-3 fatty acids, which are long-chain PUFAs found in plant and marine sources. Fish oil is very high in the PUFAs, DHA, and eicosapentaenoic acid (EPA). DHA can also be extracted from golden algae (Schizochytrium sp.). Alpha linolenic acid and other omega-3 fatty acids can be found in the seed oil of flax (Linum), black currant (Ribes), and Cannabis. Neuronal membranes contain high concentrations of DHA as well as arachidonic acid (AA); both of these essential fatty acids are crucial components of the phospholipid bilayer (each comprises approximately 25% of the phospholipid content).5 Neurotransmitter receptors lie embedded in the matrix of this membrane and their three-dimensional conformation is dependent on the fatty acids which give structure to the membrane.6
There is intriguing indirect evidence to support the possibility that lowered blood levels of certain fats may result in behavioral disturbances. Rapid lowering of blood lipids by HMG-CoA reductase inhibitors is associated with a large number of psychiatric disorders; 15% of psychiatric drug reactions were attributed to statins in a national Norwegian database.7 Reactions included aggression, nervousness, depression, anxiety, and sleeping disorders. Additional data are accumulating that suggest an association between PUFAs and serotonin, a neurotransmitter important in determining mood. Severely depressed patients have lower levels of the serotonin metabolite 5HIAA in CSF. Both cholesterol lowering therapies and low cholesterol levels have been associated with an increased risk of suicide;8-10 the prevailing theory holds that low cholesterol levels lower serotonin turnover. However, drug and diet therapies to lower cholesterol also alter essential fatty acid levels. Since essential fatty acid levels predict CSF 5-HIAA levels, and cholesterol does not,11,12 cholesterol levels may be a surrogate marker for changes in essential fatty acids.
It has been theorized that adequate long-chain PUFAs, particularly DHA, may reduce the development of depression just as they may reduce coronary artery disease.2 There appears to be an inverse relationship between the prevalence of major depression and the amount of fish consumed per capita worldwide.13 Patients with major depression have an increased ratio of AA to EPA in their plasma14,15 and erythrocytes.14-16 It was recently reported that fatty acid composition of phospholipid in erythrocyte membranes (thought to mirror neuronal membranes) of depressive patients showed significant depletions of total omega-3 PUFA, particularly DHA.17
Depletion of maternal omega-3 fatty acids has been noted during pregnancy.18 The physiology of pregnancy involves the mobilization of PUFAs from maternal stores to the fetus, and supplementation with essential fatty acids may ensure adequate supplies for the needs of the mother and the developing fetus.19,20 Hornstra et al demonstrated that maternal essential fatty acids, especially DHA, progressively decrease during pregnancy.21 These decreased levels of DHA in plasma and erythrocytes may remain low for some time postpartum, particularly in lactating women. Thus it is possible that brain levels also are low during late pregnancy and the early postpartum period and that this maternal DHA depletion may contribute to postpartum depression.
Breast Milk and Infant Formula
Breast milk, unlike infant formula, has relatively high concentrations of DHA and EPA.22 The World Health Organization recommends that DHA and EPA be added to infant formulas. European infant formulas are routinely fortified with these fatty acids, but to date the FDA has not allowed the addition of either DHA or EPA to infant formulas sold in the United States. These omega-3 fatty acids are crucial in the development of the fetal and neonatal brain and nervous system.19 Intellectual development may also suffer in infants deprived of these fatty acids. A recent study found that infants who received formula supplemented with long-chain PUFAs during their first four months performed better at 10 months of age on a problem-solving test than infants given the unsupplemented formula.23 (Dr. Cott is a pharmacologist at the National Institute of Mental Health.)
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