Docosahexaenoic acid (DHA) is a long chain polyunsaturated fatty acid found in fish. It is a member of the omega-3 family of fatty acids and can be converted to eicosapentaenoic acid (EPA) in humans. Eicosapentaenoic acid is important nutritionally because it can be converted to the series 3 eicosanoids (including thromboxanes, prostaglandins) and the series 5 leukotrienes, and these have overall anti-inflammatory effects. Inflammation is able to increase levels of oxidative stress and it is this oxidative stress that may drive many of the Western lifestyle diseases. Ensuring adequate intake of omega-3 fatty acids, in a balanced ratio to the omega-6 fatty acids, is therefore pivotal at inhibiting inflammation, oxidative stress and disease. As a deficiency of omega-3 fatty acids can increase inflammation in the brain, with a concomitant increase in oxidative stress, mental and cognitive deterioration may be related to an underlying omega-3 fatty acid imbalance. The typical Western diet is characterised by such an imbalance.
However, DHA may have protective properties on brain tissue other than in its role as a precursor to EPA. Evidence is accumulating to show that DHA is pivotal in brain development during foetal development and childhood. For example, breast fed infants have been shown to have better mental health that formula fed infants, breast milk being particularly high in DHA. In addition, low levels of DHA are associated with depression, although the cause and effect of this relationship is not understood. Supplementation of DHA to pregnant mothers also increases the problem solving ability of their infants postpartum. The role of DHA in mental health may relate to its conversion to a series of not classical eicosanoids including the resolvins and docosatrienes. These fatty acid derivatives appear important for neuronal health and function. Low levels of DHA may therefore modulate neuronal physiology and create brain imbalances and ill health. Algal sources of DHA are available to vegetarians.