Is the ratio of EPA/DHA crucial for cognitive function?
A number of population studies in the evidence-based literature indicates that higher consumptions of fish as a source of omega-3 fatty acids as DHA+EPA appears to better preserve cognitive functioning in aging populations. It should be pointed out that, for most long-term population studies investigating the relationship in this regard, the average daily intake of DHA from fish was higher (by approximately 2-3 times) than that for EPA. On the other hand, intervention trials have often utilized supplements where the EPA levels were higher that DHA and in some cases the reverse was true. Since no controlled clinical trials have directly compared equal amount of supplemental EPA+DHA in varying ratios (while retaining fixed total intakes of DHA/EPA combined), it is not known whether one fatty acid may be more beneficial than the other or whether certain ratios of these two omega-3 fatty acids may be even better for cognitive functioning in young and old alike. Although DHA is the omega-3 fatty acid which accumulates in the brain at high concentrations (in direct contrast to EPA which is present in near trace amounts), it is possible that EPA can also mediate beneficial effects by indirect mechanisms including vascular effects, blood flow, others) without necessarily having to accumulate in neuronal membranes of the brain. Until the aforementioned head-to-head clinical trials are performed, careful attention should be given to the daily intakes of EPA as well as DHA in supplemental studies since each at their corresponding levels of intake may be mediating beneficial effects. There is little or no evidence to suggest that the presence of DHA can have adverse effects on EPA mediated activities or vice-versa. While DHA intakes in North American adults average only 80 mg/day, such intakes in Japan are in the 500-1000 mg range per day via their high fish diet.