Omega 3 fats are a group of polyunsaturated fatty acids that have their first double bond 3 carbon atoms away from their methyl end. This group of fats includes the important essential dietary fat alpha linolenic acid (ALA, C18:3 (n-3)) and the fish oils eicosapentaenoic acid (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)). These fatty acids feed into a pathway that generates a number of anti-inflammatory compounds collectively known as eicosanoids and docosanoids. In this way, dietary intakes of these compounds are involved in the regulation of inflammation, and low intakes are associated with a number of Western lifestyle diseases. A large amount of research has focussed on the ability of omega 3 fatty acids to reduce the risk of cardiovascular disease, but less is known about other diseases. However, some evidence suggests that omega 3 fats may reduce the risk of depressive symptoms. This ability of the omega 3 fats to reduce depressive symptoms may relate to their anti-inflammatory effects.
Of the omega 3 fatty acids, the fish oils appear to show the best effects against the development of depression. This may relate to the fact that some of the metabolites of these fish oils are anti-inflammatory compounds that may have neuroprotective functions. These compounds, called docosatrienes or neuroprotectins (this terminology can be used interchangeably) include compounds such as neuroprotectin D1. In addition, there are a large number of anti-inflammatory compounds synthesised from EPA, called the eicosanoids, and these have general cellular anti-inflammatory effects. It is not clear how inflammation is involved in the development of depression, but there could be a direct effect through inflammation of neurones in the central nervous system. Alternatively, an omega 3 fatty acid deficiency could cause both depressive symptoms and inflammation through separate mechanisms. Either way, those with adequate intakes of omega 3 fatty acids and low level of inflammation appear to be protected from the development of depression.
For example, in one study researchers investigated the association between omega 3 fats and depressive symptoms in Puerto Rican subjects. A longitudinal analysis of the subjects was performed and an omega 3 index was calculated based on intake of DHA and EPA, expressed as a percentage of total fats. In addition, the researchers measured the depressive symptoms of the subjects. The results of the study showed that the omega 3 index of the subjects was inversely associated with the depressive symptoms experienced, such that those with the highest intake of omega 3 fats as a percentage of total fats, had the lowest levels of depressive symptoms. However, this association was only present in those with the highest urinary concentrations of 8-hydroxy-2’-deoxyguanosine (8-OHdG), a marker for inflammation. This suggests that omega 3 fats may reduce depressive symptoms by reducing an underlying high level of inflammation, and that this information could be the cause of the depressive symptoms.
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