The omega-6 to omega-3 ratio plays an important role in depression
Various biochemical mechanisms could explain the association between polyunsaturated fatty acids (PUFAs) and depression, such as: the anti-inflammatory effect of omega-3 PUFAs could modulate over-activation of the immune system associated with depression; dietary docosahexaenoic acid (DHA) deficiency has been associated with a reduction in cortical dopamine and serotonin (both involved in the cause of depression); FAs play a regulatory role in genetic transcription in the central nervous system and might also play a role in the fluidity of the neuronal membrane and receptor binding.
Various meta-analyses of observational studies have found a lower n-3 PUFA blood concentration in depressed individuals than non-depressed individuals. And numerous clinical studies performed in large samples have shown the benefits of supplementation with these FAs in depression (although the studies are very varied with regard to their characteristics).
Along the same lines were the results from a recently published study arising from the collaboration between the University of Toronto and the University of Pittsburgh, which explored the relationship between lipid metabolism and unipolar depression (major depressive disorder) and bipolar depression. To do this they assessed serum concentrations of saturated, monosaturated and polyunsaturated fatty acids in 87 patients with bipolar disorder (31 euthymic and 22 depressive) or major depressive disorder (34) and 31 non-psychiatric controls. The researchers found no significant differences between the groups with regard to total fatty acids. However, the ratios between arachidonic acid (AA) and eicosapentaenoic acid (EPA) and DHA were important: the results showed greater levels of AA:EPA and AA:EPA+DHA in patients with bipolar disorder, the AA:EPA ratio correlated positively to the duration of the unipolar disorder and the AA:EPA+DHA ratio correlated positively to the severity of the depression in all participants (all statistically significant).
These findings support the importance of the ratio between serum concentrations of omega-6 and omega-3 PUFA in depression.