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As of [[2005]], twelve vitamins and about the same number of minerals are recognized as 'essential nutrients', meaning that they must be consumed and absorbed - or, in the case of [[vitamin D]], alternatively synthesized via [[UVB radiation]] - to prevent deficiency symptoms and death. Certain vitamin-like substances found in foods, such as [[carnitine]], have also been found essential to survival and health, but these are not strictly 'essential' to eat because the body can produce them from other compounds. Moreover, thousands of different [[phytochemicals]] have recently been discovered in food (particularly in fresh vegetables), which have many discovered and yet to be discovered properties including [[antioxidant]] activity (see below). Other essential nutrients include [[essential amino acid|essential amino acids]], [[choline]] and the [[essential fatty acid|essential fatty acids]].
In addition to sufficient intake, an appropriate balance of essential fatty acids - [[omega-3]] and [[omega-6 fatty acid|omega-6]] fatty acids - has been discovered to be crucial for maintaining health. Both of these unique 'omega' long-chain [[unsaturated fat|polyunsaturated fatty acids]] are [[substrate|substrates]] for a class of [[eicosanoids]] known as [[prostaglandins]]. The omega-3 [[eicosapentaenoic acid]] ('''EPA''') (which can be made in the body from the omega-3 essential fatty acid alpha-[[linolenic acid]] ('''LNA'''), or taken in through marine food sources), serves as building block for series 3 prostaglandins (e.g. weakly-[[inflammatory|inflammation]] PGE3). The omega-6 dihomo-gamma-linolenic acid ('''DGLA''') serves as building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid ('''AA''') serves as building block for series 2 prostaglandins (e.g. pro-inflammatory PGE1). Both DGLA and AA are made from the omega-6 [[linoleic acid]] ('''LA''') in the body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which partly explains the importance of omega-3/omega-6 balance for cardiovascular health. In industrialised societies, people generally consume large amounts of processed vegetable oils that have reduced amounts of essential fatty acids in addition to a largely excessive amount of omega-6 compared to omega-3.
The rate of conversions of omega-6 DGLA to AA largely determines the production of the respective prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE1 made from AA toward anti-inflammatory PGE1 made from DGLA. Moreover, the conversion (desaturation) of DGLA to AA is controlled by the enzyme delta-5-desaturase, which in turn is controlled by hormones such as [[insulin]] (up-regulation) and [[glucagon]] (down-regulation). Because different types and amounts of food eaten/absorbed affect insulin, glucagon and other hormones to varying degrees, not only the amount of omega-3 versus omega-6 eaten but also the general composition of the diet therefore determines health implications in relation to essential fatty acids, [[inflammation]] (e.g. immune function) and [[mitosis]] (i.e. cell division).
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