Title: Is Docosahexaenoic Acid (DHA) Essential? Lessons from DHA Status Regulation, Our Ancient Diet, Epidemiology and Randomized Controlled Trials
Abstract: The human diet has changed considerably during the last 100 y. One of the striking changes is the tremendous increase in dietary fat. In terms of quality we have increased our intakes of saturated fatty acids (SFA), 2 linoleic acid (LA) and transfatty acids, concomitant with reduced intakes of (n-3) fatty acids. The latter comprises reduced intake of -linolenic acid (ALA) rich foods, and less consumption of long-chain PUFA of the (n-3) series [LC(n-3)P], i.e., eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids notably from fish (1). These dietary and other environmental changes are considered to be among the major causes of the rapid expansion of diet-related chronic disease (2), including cardiovascular disease (CVD) in the past century. Our genetic constitution is unlikely to have kept pace with the changing diet. Today’s nutritional habits are consequently not the same as those on which our genes are based (2). The return to basics may be indicated, but we unfortunately have no reliable knowledge of the ancient diet on which our genes evolved. In this literature study we seek to find whether LC(n-3)P, and notably DHA, are essential. Essential fatty acid (EFA) metabolism and function. The parent essential fatty acids (EFA), LA and ALA cannot be synthesized in the human body and are therefore indispensable components of our diet. Both LA and ALA may be converted by chain elongation, desaturation and chain-shortening into their respective long-chain metabolites, collectively named LCP (20 carbon atoms and 3 double bonds). The most important LCP of the (n-6) fatty acid series is arachidonic acid (AA), whereas EPA and DHA are the major LC(n-3)P. LCP may also be derived from the diet. High contents are present in meat (AA) and fish (EPA, DHA). AA and DHA are especially abundant in the brain and the retina. Both LCP and their parent precursors may serve for energy generation, but LCP are relatively protected from -oxidation compared with their parents. AA and DHA are important building blocks of structural lipids. LCP in phospholipids contribute to membrane properties like fluidity, flexibility, permeability and modulation of membrane-bound. DHA in retina and postsynaptic membranes is crucial for adequate functioning of embedded proteins, i.e., rhodopsin for vision and postsynaptic receptors for neurotransmission. AA, EPA and dihomo--linolenic acid (DGLA), liberated from membrane phospholipids, are precursors of short-lived highly potent regulatory hormones collectively named eicosanoids. These play important roles in inflammatory reactions, blood pressure control and platelet aggregation. Eicosanoids from AA are involved in vasoconstriction/platelet aggregation (TxA 2 ), inhibition of vasodilatation/platelet aggregation (prostaglandin I2), inflammation, and leukocyte che